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The measurements were made of the unidirectional potassium fluxes, the rate constants and the permeability coefficient. At external potassium 2.5 mM, the outflux and influx are 10--15, and 22-29 micromol/h g d. wt, respectively, and the net flux is comparable with the unidirectional fluxes. At external potassium 75 mM, the unidirectional fluxes increase up to 70--80 micromol/h, g d. wt. and the net flux does not exceed 0.1 of the unidirectional one. The outflux rate constant/influx rate constant ratio for both the potassium concentrations is about 1.5 times below the Ussing's ratio. This effect cannot be accounted for the single file phenomenon since it is independent of the direction and value of the net potassium flux. The discrepancy between the measured membrane potential and EK may, to some extent, be due to peculiarities of potassium movement.
1. Single-unit activity was recorded from S1 dorsal root afferent fibers in pentobarbital-anesthetized rats. In 25 experiments, 245 afferent fibers were identified by electrical stimulation of the pelvic nerve. Fifty-two percent were C fibers (conduction velocity: 1.70 +/- 0.04 m/s; mean +/- SE) and 48% were A delta-fibers (conduction velocity: 11.07 +/- 0.95 m/s). 2. Of 245 pelvic nerve afferent fibers, 92 (38%) responded to noxious urinary bladder distension (UBD; 80 mmHg); 57 of these fibers were C fibers and 35 were A delta-fibers. Forty-four fibers responded to colorectal distension (CRD; 80 mmHg); 32 were C fibers and 12 were A delta-fibers. A total of 39 fibers were identified in the anal mucosa; 3 were C fibers and 36 were A delta-fibers. Seventy fibers (28%) in these experiments were unresponsive to either UBD or CRD or to probing of the anal mucosa; 32 were unmyelinated C fibers and 38 were A delta-fibers. 3. Reproducibility of responses to repeated UBD (80 mmHg, 20 s; 8 trials at 4-min intervals) was tested in 10 fibers. In nine fibers, responses to repeated distension did not change; one fiber exhibited a progressive decrease in response magnitude after the third trial. 4. Of the 92 afferent fibers that responded to UBD, 45 were further characterized for responses to graded intensities of UBD. Forty fibers had some resting activity (1.7 +/- 0.3 impulses/s) and five fibers exhibited no ongoing activity. The response to UBD adapted slowly during the 20-s period of phasic UBD or during slow isotonic filling of the bladder. 5. The stimulus-response function (SRF) of fibers (n = 45) to graded UBD was monotonic < or = 80 mmHg. Thresholds for responses were determined after extrapolation of the least-squares linear regression line to the ordinate, and varied between 0 and 45 mmHg. The frequency distribution profile of thresholds revealed two populations of pelvic nerve afferent fibers in the urinary bladder: a larger group (n = 36) of low-threshold (LT) fibers (5.7 +/- 1.0 mmHg) and a smaller group (n = 9) of high-threshold (HT) fibers (34 +/- 2.5 mmHg). 6. Responses of four LT fibers to graded UBD were tested before and 30 min after instillation of 0.5 ml of 0.5% acetic acid (pH 3) into the bladder. The mean threshold for response of these fibers before instillation of acetic acid (9.4 +/- 3.1 mmHg) more than doubled (to 22.3 +/- 6.7 mmHg) after instillation of acetic acid.(ABSTRACT TRUNCATED AT 400 WORDS)
Aramid fibers from aromatic polyamide group are plastic materials with high mechanical resistance to breaking, small elongation and low mass. They have obtained numerous technical usage for products carrying high mechanical forces and resistance to consumption. Application of aramid in alloplasty would satisfy the grafts with high mechanical resistance. However, the biological influence and biostability of aramid is unknown and univocal. Research of the degree of biocompatibility of aramid fibres in comparison with commonly used polyester fibres with known and accepted biological reaction was the purpose of the study. The research included in the first phase: physicochemic properties, hemolytic action, cytotoxity degree, intracutaneous reactivity of aqueous extracts, in the second phase: estimation of tissue reaction after implantation the early and distant period, estimation of systemic and local induction of proinflammatory cytokines IL-1beta ad IL-6 after implantation. In physicochemic studies of aqueous extracts from fibers proper electric conductivity and dry residue were determined. The research of toxic action was carried out on frozen sperm of a bull estimating the survival time of sperm cells in the tested aqueous extracts. The estimation of hemolytic was conducted on human erythrocytes according to the method based on photometric measurement of blood supernatant and aqueous extracts. The research of irritating action measured with the changes of colour and size reaction after intracutaneous injection of aqueous extracts was carried out on rabbits. The research of the local reaction of soft tissue after implanting of aramid and polyester fibers into back muscles and into the peritoneal cavity was carried on 90 rats. Estimation was performed in early period, that is to 90th, and distant period, that is to the 360th day after implantation. The estimation of the local reaction of cartilaginous tissue was performed on 24 rabbits after implantation on 60, 90, 180, 270 and 360 days of aramid and polyester fibers into xiphoid process of sternum. The quantitative microscopic estimation of the local reaction of tissue after implantation of fibers was performed using punctual estimation of tissue reaction. The research of proinflammatory cytokines IL-1beta and IL-6 induction after implantation of aramid and fibers into peritoneal cavity was performed on 85 mice Balb/c. the level IL-1beta and IL-6 was determined in the serum of peripheral blood of mouse and in peritoneal fluid in 3rd, 7th, 14th and 21st day after implantation. The results were compared with control of operative and spontaneous production of proinflammatory cytokines in non-operated animals. A rubber medical drain constituted the control of the tested cytokines induction. The determinations were made with ELISA method. The tests of resistance to biocorrosion in electronic scanning microscope were performed after implantation of fibers into peritoneal cavity of rats for 180 and 360 days. Biostability of mechanical properties of fibers after remaining for 360 days in the application of the tested breaking force in the knot and in the dynamic system of cyclic strain of fibers (with strength 20N and 1Hz). In the tests of aqueous extracts from fibers comparative pH (aramid--6.42 and polyester 6.35), four-time higher proper electric conductivity (aramid 45.5; polyester 11.0) and five-time higher-dry mass of residue after vaporization of extracts from aramid fibers in comparison with polyester fibers (aramid--10.4 mg, polyester--2.1 mg) were observed. In biological tests of aqueous extracts toxic, hemolytic or irritating action was not observed. The local reaction soft tissues after implantation of aramid and polyester fibers was similar. Macroscopically it was characterized with producing on the third day thin, transparent membrane which in distant period, was whitish, thicker and strongly connected with the implanted fibers and surrounding tissues. In the microscopic tests the reaction was characterized with a short-lasting exudative phase less intense around the aramid fibers and a proliferating phase led to producing a capsule from newly created areolar tissue sharply separated from muscles undergoing collagenization in the cicatrization phase. The produced connective tissue capsule from the side of the graft both around aramid and polyester had the cellular character with the presence of single giant multinucleated cells till the 360th day after implantation. From the side of the muscles the connective tissue streak had more dense character and in distant period consisted mainly of collagenous fibers with hyalinization features. The reaction of cartilaginous tissue after implantation both kinds of fibers from the 90th to the 360th day was similar. It was characterized with producing cartilaginous tissue and locally fibrous tissue with a large amount of intercellular substance. Connective tissue showed hyalinization features and was transformed into cartilaginous tissue. According to the punctual estimation of reaction the tested fibers caused minimal reaction. In the testes of level of proinflammatory cytokines IL-1beta and IL-6 their constant presence on the low level in the serum of mouse blood and in the peritoneal fluid was observed. aramid fibers did not induce an increase of the level IL-1beta and IL-6, whereas polyester fibers in the 3rd day after surgery stimulated locally their moderate increase. The influence of surgery on the local induction IL-1beta and IL-6 was statistically essential in the 3rd day. The rubber medical drain was strong inductor of mediators of inflammation IL-1beta and IL-6. In physiocomechanical fatigue-testing and in SEM in the period to 360th day after implantation, biocorrosion of aramid and polyester fibers was not observed. The value of breaking force of aramid fibers was twice higher and the resistance to cyclic fatigue was over two hundred times higher in comparison to polyester fibers. Those differences were statistically significant (p < 0.001). On the basis of the performed tests it is possible observed that aramid fibers cause minimal tissue reaction compared with the observed one around polyester fibers, they do not cause local nor systemic stimulation of proinflammatory cytokines IL-1beta and IL-6. aramid fibers show essentially higher statistic and dynamic mechanical resistance in comparison with polyester fibers; they not undergo biocorosion and they can be useful to increase mechanical resistance of medical materials or as independent biomaterial resistant to high mechanical forces.
1. Single-unit activity was recorded from S1 sacral dorsal root afferent fibers in the anesthetized rat. A total of 364 afferent fibers were identified by electrical stimulation of the pelvic nerve and subsequently tested for response to colorectal distension (CRD) and urinary bladder distension (UBD). Sixty-seven percent (n = 244) of the fibers were unmyelinated C-fibers and 33% (n = 120) were thinly myelinated A delta-fibers. 2. In three initial experiments, 35 fibers were identified by pelvic nerve stimulation and tested for response only to CRD; none of these fibers responded to CRD. In 20 subsequent experiments, 329 pelvic nerve afferent fibers were tested for response to CRD and UBD. Thirty-four percent (n = 112) of the 329 fibers were unresponsive to noxious CRD (80 mmHg) or to UBD (slow filling < or = 100 mmHg), 44% (n = 146) responded to UBD, 16% (n = 53) responded to CRD, and 6% (n = 18) responded to mechanical stimulation of the anal mucosa. 3. Of the total of 53 pelvic nerve afferent fibers that responded to CRD, 43 (81%) were C-fibers (mean: 1.5 m/s) and 10 (19%) were A delta-fibers (mean: 4.7 m/s). Fifteen of the CRD-sensitive fibers had no resting activity, whereas 38 fibers exhibited some resting activity (mean: 2.6 imp/s). 4. Reproducibility of responses to repeated CRD (80 mmHg, 30s, 10 trials at 4-min intervals) was tested in 17 fibers. In 16, responses to repeated distension were reproducible without evidence of facilitation or inhibition of subsequent responses. One fiber gave greater responses during the 9th and 10th trials. 5. Responses to graded CRD were studied in 44 fibers. All fibers exhibited monotonic, increasing stimulus-response functions < or = 80 mmHg of distension. Thresholds for response of the 44 fibers were determined after extrapolation of the least-squares linear-regression line to the ordinate and varied between 0 and 40 mmHg. Two populations of pelvic nerve afferent fibers in the colon were apparent: low threshold (LT) afferent fibers had a mean threshold of 2.9 mmHg (range: 0-10 mmHg; n = 34) and high threshold (HT) afferent fibers had a mean threshold of 32.6 mmHg (range: 28.0-40.0 mmHg; n = 10). 6. Chemosensitivity to bradykinin (BK) was tested in nine LT fibers. Seven fibers responded to BK (0.1 to 100 micrograms/kg ia) and two fibers did not respond up to 100 micrograms/kg of BK. Responses to BK tested in three fibers were dose dependent.(ABSTRACT TRUNCATED AT 400 WORDS)
BACKGROUND: Dietary fiber is known to influence bowel habit and gastrointestinal mucosal cell morphology and function. large-bowel function is particularly influenced by insoluble, poorly fermentable fiber sources, whereas mucosal function is affected by fiber sources that are soluble and highly fermentable. The aim of the present study was to compare bowel function during consumption of a self-selected diet, a fiber-free enteral diet, and three polymeric enteral diets, each supplemented with a fiber with different fermentation characteristics. The fiber sources used were oat, soy oligosaccharide, and soy polysaccharide. METHODS: Seven healthy subjects consumed four diets in random order for 4 to 7 days. These were a self-selected diet, a 2-L polymeric enteral diet, and a 2-L polymeric enteral diet supplemented with 15 g of total dietary fiber per liter derived from either soy oligosaccharide fiber (75 g/L) or oat fiber (15 g/L). An additional six healthy subjects were randomly assigned to three diets (4 to 7 days): a self-selected diet, a 2-L polymeric enteral diet, or the same 2-L polymeric enteral diet supplemented with 20 g of soy polysaccharide fiber per liter (15 g of total dietary fiber per liter). Bowel function was assessed by measuring whole-gut transit time, mean daily stool wet weights, and bowel movement frequency per day. Fermentation characteristics of the different fiber sources were determined quantitatively and qualitatively by measuring short-chain fatty acids produced during in vitro stool culture. RESULTS: Total short-chain fatty acid and butyric acid production with soy oligosaccharide fiber were significantly higher compared with values observed for soy polysaccharide fiber (p < .003), oat fiber (p < .005), and self-selected (control) diet (p < .003). Compared with the fiber-free diet, consumption of the soy polysaccharide, oat, and soy oligosaccharide-fiber-supplemented enteral diets did not significantly (p > .05) alter whole-gut transit time or stool wet weight. However, bowel frequency was significantly improved by consumption of the soy polysaccharide-fiber-supplemented diet but not the oat fiber or soy oligosaccharide-fiber-supplemented diets. CONCLUSION: Compared with a fiber-free polymeric enteral diet, the daily consumption of an enteral diet supplemented with 30 g of total dietary fiber per day derived from a poorly fermentable oat fiber, a highly fermentable soy oligosaccharide fiber, or a moderately fermentable soy polysaccharide fiber has little impact, if any, on bowel function.
We have shown previously that asbestos and other mineral dusts, including glass fibers, induce cell transformation and chromosomal mutations in Syrian hamster embryo cells in culture. In the present study, we observed that both asbestos and glass fibers were phagocytized by these cells and accumulated in the perinuclear region of the cytoplasm. In order to understand the mechanism of fiber length-dependent cellular effects, we examined the phagocytosis and intracellular distribution of glass fibers of differing lengths in cells at various times after treatment. Glass fiber length was decreased by milling with a mortar and pestle. Cells treated with an equal dose of milled glass fibers (on a weight per surface area basis) were exposed to 7-fold more fibers since milling of glass fibers resulted in a 7-fold decrease in length with little change in diameter. However, cells exposed to milled glass fibers phagocytized a similar number of fibers as cells exposed to an equal mass of unmilled glass fibers, indicating that milled fibers were less readily phagocytized. In cells treated with either unmilled or milled glass fibers, the length of the intracellular fibers was more than 2-fold greater than the length of the fibers on the surface, suggesting that cells selectively internalized longer fibers. Fiber length, however, did not appear to affect the migration of intracellular fibers to the perinuclear region of the cytoplasm. Even though cells treated with milled glass fibers contained a similar number of fibers as those treated with unmilled glass fibers, the resulting cytotoxicity, transformation frequency, and frequency of micronuclei were greatly reduced in the cultures treated with milled glass fibers. Thus, fiber length appears to affect the phagocytosis of fibers as well as the ability of intracellular fibers to induce cytogenetic damage and the resultant transformation.
A description is provided of the ratio of slow-tonic vs. slow- and fast-twitch fibers for five muscles in the adult turtle, Pseudemys (Trachemys) scripta elegans. The cross-sectional area of each fiber type and an estimation of the relative (weighted) cross-sectional area occupied by the different fiber types are also provided. Two hindlimb muscles (flexor digitorum longus, FDL; external gastrocnemius, EG) were selected on the basis of their suitability for future motor-unit studies. Three neck muscles (the fourth head of testo-cervicis, TeC4; the fourth head of retrahens capitus collique, RCCQ4; transversalis cervicis, TrC) were chosen for their progressively decreasing oxidative capacity. Serial sections were stained for myosin adenosine triphosphatase (ATPase), NADH-diaphorase, and alpha-glycerophosphate dehydrogenase (alpha-GPDH). Conventional fiber-type classification was then performed using indirect markers for contraction speed and oxidative (aerobic) vs. glycolytic (anaerobic) metabolism: i.e., slow oxidative (SO, including slow-twitch and possibly slow-tonic fibers), fast-twitch, oxidative-glycolytic (FOG), and fast-twitch glycolytic (Fg) fibers. Slow-tonic fibers in the SO class were then revealed by directing the monoclonal antibody, ALD-58 (raised against the slow-tonic fiber myosin heavy chain of chicken anterior latissimus dorsi), to additional muscle cross sections. All five of the tested muscles contained the four fiber types, with the ATPase-stained fibers including both slow-tonic and slow-twitch fibers. The extreme distributions of SO fibers were in the predominately glycolytic TrC vs. the predominately oxidative TeC4 muscle (TrC-SO, 9%; FOG, 20%; Fg, 71% vs. TeC4-SO, 58%: FOG, 16%; Fg, 25%). Across the five muscles, the relative prevalence of slow-tonic fibers (4-47%) paralleled that of the SO fibers (9-58%). TeC4 had the highest prevalence of slow-tonic fibers (47%). The test muscles exhibited varying degrees of regional concentration of each fiber type, with the distribution of slow-tonic fibers paralleling that of the SO fibers. In the five test muscles, fiber cross-sectional area was usually ranked Fg > FOG > SO, and slow-twitch always > slow-tonic. In terms of weighted cross-sectional area, which provides a coarse-grain measure of each fiber type's potential contribution to whole muscle force, all five muscles exhibited a higher Fg and lower SO contribution to cross-sectional area than suggested by their corresponding fiber-type prevalence. This was also the case for the slow-twitch vs. slow-tonic fibers. We conclude that slow-tonic fibers are widespread in turtle muscle. The weighted cross-sectional area evidence suggested, however, that their contribution to force generation is minor except in highly oxidative muscles, with a special functional role, like TeC4. There is discussion of: 1) the relationship between the present results and previous work on homologous neck and hindlimb muscles in other nonmammalian species, and 2) the potential motoneuronal innervation of slow-tonic fibers in turtle hindlimb muscles.
The carcinogenic potential in the intraperitoneal cavity of three newly developed biosoluble insulation glass wool fibers (M, P, and V) and one newly developed biosoluble insulation stone wool fiber (O) was investigated and compared to that of a previously developed soluble glass fiber (B). The in vitro dissolution coefficient of the three glass wool fibers ranged from 450 to 1037 ng/cm(2) x h and was 523 ng/cm(2) x h for the stone wool fiber. The in vitro dissolution coefficient of the B fiber was 580 ng/cm(2) x h. Groups of female Wistar rats (strain Crl: Wi BR) were exposed by repeated injections to doses of 0.5, 2, and 5 x 10(9) WHO fibers, which corresponds to between 41 mg to 724 mg fiber injected. In addition, 2 groups of crocidolite were used as positive controls at doses of 0.1 x 10(9) and 1 x 10(9) WHO fibers (0.5 and 5 mg). The in vitro dissolution coefficient of crocidolite is estimated to be approximately 1 ng/cm(2) x h. The protocol of the study and the size distribution of the test samples conformed to the European Commission Protocol EUR 18748 EN, and the study was executed under Good Laboratory Practice conditions. Two of the new insulation wools, fibers M and 0, showed no statistically significant tumorigenic response even at the very high dose of 5 x 10(9) WHO fibers injected. Fibers P and V showed a small tumorigenic response in the ip cavity similar in magnitude to the B fiber, which has been declared in the German fiber regulations as a noncarcinogenic fiber. The response to the soluble insulation fibers was notably different from that of the known carcinogen crocidolite, which produced 53% tumors at a comparatively low dose of 0.1 x 10(9) WHO fibers. The incidence of mesothelioma was found to be highly correlated to the incidence of intra-abdominal nodules and masses at different sites. The incidence of abdominal nodules and masses was highly correlated to the number of animals with ascites. The incidence of chronic peritonitis with fibrotic nodules at different organs also correlated with the incidence of mesotheliomas. Differences in etiology were observed between the massive doses of the highly soluble insulation wools when injected directly into the ip cavity and the lower doses of the extremely insoluble fiber crocidolite. The variability in this reaction and the impairment of animal health put into question the value of these massive doses in evaluating the carcinogenic response of soluble insulation wools. All of the fibers tested fulfilled the exoneration criteria with respect to carcinogenicity according to the European Directive 97/69/EC ("an appropriate intra-peritoneal test has not expressed signs of excessive carcinogenicity"). The dose as defined in the EC-Protocol EUR 18748 EN was 1 x 10(9) WHO fibers with a defined geometric spectrum. The influence of fiber dimensions on the ip tumor response and the difficulty in assessing the influence of the difference in background levels between this and previous studies make direct application of the German TRGS 905 criteria difficult; however, by comparison to fiber B, which in the TRGS 905 is considered as a noncarcinogenic fiber, all of the synthetic mineral fiber types tested in this study also appear to meet the intended German criteria for exoneration.
The principal aim of this work was to better understand how regenerating muscle fibers become innervated in adult animals. To induce muscle regeneration, individual identified muscle fibers in a mouse were damaged with a laser focused through a microscope. The muscle fiber that degenerated and the muscle fiber that was formed in its place were followed by viewing the same site repeatedly over a period of 2 d to 40 weeks. Commonly, the nerve terminal innervating the irradiated muscle fiber partially retracted during muscle fiber degeneration, and then sprouted to innervate the regenerating muscle fiber at the same site it had previously innervated the muscle fiber that was damaged. During the early phase of muscle regeneration we also observed sprouts originating from nerve terminals on adjacent muscle fibers. The new nerve growth was a response to the regenerating muscle fiber rather than to the degenerated fiber it replaced because repeated damage of the same site every 2-3 d over a 10 d period (to prevent regeneration) did not cause any sprouting. The direction of the sprouts on adjacent muscle fibers showed a bias toward the regenerating muscle fiber, although they avoided the region occupied by the original nerve terminal. Forty percent of the sprouts managed to reach the regenerated fiber. Nonetheless, by 11 d after muscle fiber damage, all sprouts had regressed, leaving the new fiber innervated by the same motor axon that innervated the fiber that was damaged. On the other hand, when the overlying nerve terminal as well as the muscle fiber was damaged, the sprouts from nearby muscle fibers were both more numerous and more stable, and in five cases we observed two or more new synaptic junctions on the regenerating fiber originating from different axons. In one case we witnessed a protracted competition between the original motor axon as it sprouted back and the sprouts from nearby junctions for sole innervation of the regenerate. Ultimately, the surviving sprouts myelinated and became the permanent and exclusive input to the new fiber. These results indicate that regenerating muscle fibers emit a signal that induces directional sprouting from nearby undamaged nerve terminals. Reinnervation of the regenerating muscle fiber by one axon apparently prevents the maintenance of such neurites. Because the process of muscle regeneration shares many features in common with myogenesis during embryonic development, it is likely that developing muscle fibers present an analogous stimulus to ingrowing motor axons.(ABSTRACT TRUNCATED AT 400 WORDS)
1. Transient, stretch-evoked force responses of chemically skinned muscle fibers from the cat hindlimb were investigated. The purpose of these experiments was to determine the exent to which short-range stiffness, the apparent stiffness exerted by the fiber over the first 0.5% of length change, is higher in type I than type II muscle fibers. Fibers were obtained from soleus and vastus intermedius muscles, which contain predominantly type I fibers, the LGm, a compartment of the lateral gastrocnemius muscle that contains predominantly type II fibers, and LG3, a compartment of mixed type. 2. Beyond a short range of approximately 1% of muscle length during a 0.5 muscle length/s (ML/s) stretch, most fibers exhibited an abrupt decrease in apparent stiffness or yield. Fibers from the muscles containing predominantly type S (slow twitch, or type I) fibers, soleus and vastus intermedius, exhibited such a pronounced decline in apparent stiffness that force declined as well during continued stretch. Most of the fibers from the LG3 compartment could be divided into two distinct groups depending upon whether or not they showed a force yield at the stretch velocity of 0.5 ML/s. 3. The short-range stiffness measured over the first 0.5% of stretch was greater for fibers showing force yield than for those that did not at matched initial forces and normalized stretch amplitudes. This result is consistent with the hypothesis that the same mechanism that endows the fiber with high short-range stiffness is also responsible for a greater extent of yielding. 4. Fibers from soleus were found to exhibit a force yield over a 200-fold range of velocities (0.01-2 ML/s). In contrast, most fibers from the LGm compartment showed only an increase in extent of yield with stretch velocity. Some of these fibers eventually yielded in force, but only when they were stretched at velocities > 2 ML/s. The proposed relationship between high short-range stiffness and yielding was supported by the finding that short-range stiffness increased sharply in the range of velocities where the fiber showed the greatest increase in extent of yield. 5. After the physiological experiments, fibers were subjected to SDS gel electrophoresis. Two distinct patterns of bands in the low molecular weight range were found to correspond to the two types that were identified on the basis of their dynamic mechanical properties. Fibers that did not yield at 0.5 ML/s showed a band pattern very similar to that of rabbit psoas (type II) fibers. 6. These results support the hypothesis that type I fibers are specialized in presenting a high short-range stiffness for effective postural control in advance of reflex mechanisms and that this property results from intrinsic properties of the fiber and is not due to differences in the dimensions of type I and II fibers. Yielding serves to protect the fiber from damaging levels of force during lengthening contractions. The importance of these transient properties to the mechanical behavior of muscle during ongoing movements is suggested by the observation that high stiffness followed by yielding is repeated with little alteration during successive stretches.
Some adult cranial muscles have been reported to contain unusual myosin heavy-chain (MHC) isoforms (i.e., slow-tonic, alpha-cardiac, embryonic, and neonatal), which exhibit distinct contractile properties. In this study, adult human mylohyoid (MH) muscles obtained from autopsies were investigated to detect the unusual MHC isoforms. For comparison, the biceps brachii and masseter muscles of the same subjects were also examined. Serial cross-sections from the muscles studied were incubated with a panel of isoform-specific anti-MHC monoclonal antibodies that distinguish major and unusual MHC isoforms. On average, the slow type I and fast type II MHC-containing fibers in the MH muscle accounted for 54% and 46% of the fibers, respectively. In contrast to limb and trunk muscles, the adult human MH muscle was characterized by a large proportion of hybrid fibers (85%) and a small percentage of pure fibers (15%; P < 0.01). Of the fast fiber types, the proportion of the type IIa MHC-containing fibers (92%) was much greater than that of the type IIx MHC-containing fibers (8%; P < 0.01). Our data demonstrated that the adult human MH fibers expressed the unusual MHC isoforms that were also identified in the masseter, but not in the biceps brachii. These isoforms were demonstrated by immunocytochemistry and confirmed by electrophoretic immunoblotting. Fiber-to-fiber comparisons showed that the unusual MHC isoforms were coexpressed with the major MHC isoforms (i.e., MHCI, IIa, and IIx), thus forming various major/unusual (or m/u) MHC hybrid fiber types. Interestingly, the unusual MHC isoforms were expressed in a fiber type-specific manner. The slow-tonic and alpha-cardiac MHC isoforms were coexpressed predominantly with slow type I MHC isoform, whereas the developmental MHC isoforms (i.e., embryonic and neonatal) coexisted primarily with fast type IIa MHC isoform. There were no MH fibers that expressed exclusively unusual MHC isoforms. Approximately 81% of the slow type I MHC-containing fibers expressed slow-tonic and alpha-cardiac MHC isoforms, whereas 80% of the fast type IIa MHC-containing fibers expressed neonatal MHC isoform. The m/u hybrid fibers (82% of the total fiber population) were found to constitute the predominant fiber types in the adult human MH muscle. At least seven m/u MHC hybrid fiber types were identified in the adult human MH muscle. The most common m/u hybrid fiber types were found to be the MHCI/slow-tonic/alpha-cardiac and MHCIIa/neonatal, which accounted for 39% and 33% of the total fiber population, respectively. The multiplicity of MHC isoforms in the adult MH fibers is believed to be related to embryonic origin, innervation pattern, and unique functional requirements.
The effects of 14 days of spaceflight on myonuclear number, fiber size, and myosin heavy chain (MHC) expression in isolated rat soleus muscle fiber segments were studied. Single soleus muscle fibers from rats flown on the Spacelab Life Sciences-2 14-day mission were compared with those from age-matched ground-based control rats by using confocal microscopy and gel electrophoresis. Spaceflight resulted in a significant reduction in the number of fibers expressing type I MHC and an increase in the number of fibers expressing type IIx or IIa MHC. Space-flight also resulted in an increase in the percentage of fibers coexpressing more than one MHC and in the reexpression of the neonatal isoform of MHC in some fibers. Fiber cross-sectional area was significantly reduced in pure type I MHC-expressing fibers and in fibers coexpressing type I+II MHC but not in fibers expressing one or more type II MHC in the flight rats. The number of myonuclei per millimeter was significantly reduced in type I MHC-expressing fibers from the flight rats but was not significantly different in type I+II and type II MHC-coexpressing fibers. Fibers expressing neonatal MHC were similar in size to control fibers but had significantly fewer myonuclei per millimeter than flight fibers not expressing neonatal MHC. In type I MHC-expressing fibers, the reduction in fiber cross-sectional area was greater than the reduction in myonuclear number; thus the average cytoplasmic volume per myonucleus was significantly lower in flight than in control fibers. The reduction in both myonuclear number and fiber size of fibers expressing type I MHC after 14 days of spaceflight supports the hypothesis that changes in the number of myonuclei may be a contributing factor to the reduction in fiber size associated with chronic unloading of the musculature.
A water-based calcium phosphate cement (CPC) has been used in a number of medical and dental procedures due to its excellent osteoconductivity and bone replacement capability. However, the low tensile strength of CPC prohibits its use in many unsupported defects and stress-bearing locations. Little investigation has been carried out on the fiber reinforcement of CPC. The aims of the present study, therefore, were to examine whether fibers would strengthen CPC, and to investigate the effects of fiber type, fiber length, and volume fraction. Four different fibers were used: aramid, carbon, E-glass, and polyglactin. Fiber length ranged from 3-200 mm, and fiber volume fraction ranged from 1.9-9.5%. The fibers were mixed with CPC paste and placed into molds of 3 x 4 x 25 mm. A flexural test was used to fracture the set specimens and to measure the ultimate strength, work-of-fracture, and elastic modulus. Scanning electron microscopy was used to examine specimen fracture surfaces. Fiber type had significant effects on composite properties. The composite ultimate strength in MPa (mean +/- SD; n = 6) was (62+/-16) for aramid, (59+/-11) for carbon, (29+/-8) for E-glass, and (24+/-4) for polyglactin, with 5.7% volume fraction and 75 mm fiber length. In comparison, the strength of unreinforced CPC was (13+/-3). Fiber length also played an important role. For composites containing 5.7% aramid fibers, the ultimate strength was (24+/-3) for 3 mm fibers, (36+/-13) for 8 mm fibers, (48 +/-14) for 25 mm fibers, and (62+/-16) for 75 mm fibers. At 25 mm fiber length, the ultimate strength of CPC composite was found to be linearly proportional to fiber strength. In conclusion, a self-setting calcium phosphate cement was substantially strengthened via fiber reinforcement. Fiber length, fiber volume fraction, and fiber strength were found to be key microstructural parameters that controlled the mechanical properties of CPC composites.
This study examined two putative mechanisms of new fiber formation in postnatal skeletal muscle, namely longitudinal fragmentation of existing fibers and de novo formation. The relative contributions of these two mechanisms to fiber formation in hypertrophying anterior latissimus dorsi (ALD) muscle were assessed by quantitative analysis of their nuclear populations. Muscle hypertrophy was induced by wing-weighting for 1 week. All nuclei formed during the weighting period were labeled by continuous infusion of 5-bromo-2'-deoxyuridine (BrdU), a thymidine analog, and embryonic-like fibers were identified using an antibody to ventricular-like embryonic (V-EMB) myosin. The number of BrdU-labeled and unlabeled nuclei in V-EMB-positive fibers were counted. Wing-weighting resulted in significant muscle enlargement and the appearance of many V-EMB+ fibers. The majority of V-EMB+ fibers were completely independent of mature fibers and had a nuclear density characteristics of developing fibers. Furthermore, nearly 100% of the nuclei in independent V-EMB+ fibers were labeled. These findings strongly suggest that most V-EMB+ fibers were nascent fibers formed de novo during the weighting period by satellite cell activation and fusion. Nascent fibers were found primarily in the space between fascicles where they formed a complex anastomosing network of fibers running at angles to one another. Although wing-weighting induced an increase in the number of branched fibers, there was no evidence that V-EMB+ fibers were formed by longitudinal fragmentation. The location of newly formed fibers in wing-weighted and regenerating ALD muscle was compared to determine whether satellite cells in the ALD muscle were unusual in that, if stimulated to divide, they would form fibers in the inter- and intrafascicular space. In contrast to wing-weighted muscle, nascent fibers were always found closely associated with necrotic fibers. These results suggest that wing-weighting is not simply another model of regeneration, but rather produces a unique environment which induces satellite cell migration and subsequent fiber formation in the interfascicular space. De novo fiber formation is apparently the principal mechanism for the hyperplasia reported to occur in the ALD muscle undergoing hypertrophy induced by wing-weighting.
We compared the impact of various energy settings, frequency, and fiber diameters on the stone fragmentation capabilities of the holmium laser. Stone phantoms, made from plaster of Paris and uniform in weight, were treated with one of two laser fiber sizes: small (200 and 365 microm) and large (550 and 1000 microm). Stones were immersed in water and fragmented for 3 minutes at 0.5, 1.0, or 2.0 J and 5, 10, or 15 Hz. The mean percentage decrease in weight in the two groups was compared using one-way ANOVA. The effect on flexible ureterorenoscope deflection of the small fibers was tested in two different ureterorenoscopes. Raising the energy level when using the small fibers resulted in more weight loss (P < 0.05). Increasing the frequency up to 10 Hz also resulted in a significant increase in weight loss (P < 0.05), yet above 10 Hz, there was no significant additional weight loss noted for either small fiber. There was no significant difference in the weight loss produced by the two fibers unless the energy setting was >1.0 J. Studies with the large fibers demonstrated similar results, with significant increments of weight loss occurring with increased energy (P < 0.05), while nonsignificant differences were seen for the two fiber diameters. Increasing laser frequency up to 15 Hz resulted in a significant increase in weight loss for the large fibers. Loss of ureterorenoscope deflection ranged from 7% to 16% and 18% to 37% for the 200-microm and 365-microm fibers, respectively. Small-diameter fibers, in combination with semirigid or flexible ureteroscopes, should be used to treat upper urinary tract stones. The 365-microm fiber should be utilized for the management of ureteral stones, as minimal endoscopic deflection is required to access these calculi. Because the 200-microm fibers are considerably more expensive, their use should be reserved for fragmentation of intrarenal calculi, where maximum deflection is required during flexible ureterorenoscopy. The ideal energy and frequency settings for the small fibers are <1.0 J and 5 to 10 Hz. Larger fibers can be used for managing bladder or renal calculi, as there is no need for significant fiber deflection. The 550-microm fiber is preferred, as it is comparable in efficacy to the 1000-microm fiber and is less expensive. Energy and frequency can be maximized to 2.0 J and 15 Hz without damage to the fiber, but visibility can be affected by high frequencies. Appropriate fiber selection and energy/frequency settings will allow access to most stones throughout the urinary tract, maximize fiber life, and minimize fiber expense.
The elastic fiber system in the human tracheal and bronchial mucosa was studied by light and electron microscopy. Elastic fibers, elaunin fibers, and oxytalan fibers were discerned. These fibers were identified by means of their staining characteristics (elastica stains, methods for disulfide-groups) and on account of their fine structural morphology. Elastic fibers consist of elastin and few "elastic-fiber microfibrils". The relative amount of elastin (compared to the amount of elastic-fiber microfibrils) is large in elastic fibers but small in elaunin fibers. Oxytalan fibers - by contrast - are pure bundles of microfibrils. In the light microscope a well-defined elastic lamina separates the lamina propria and the submucosa of the normal mucous membrane. The elastic lamina is formed by coarse strands of longitudinally running elastic fibers. A delicate network of elastica-positive fibers is attached to the basement membrane of the epithelial layer (subepithelial elastic layer). A few of these elastica-positive fibers branch out, traverse the region of the thickened basement membrane, and insert into the basal lamina of the epithelium. A loose network of elastica-positive fibers is present both in the lamina propria and in the submucosa. Plates of cartilage, glandular epithelium, and bundles of smooth muscle cells are enveloped by delicate elastica-positive fibers. Electron microscopy shows the lamina elastica to be predominantly composed of elastic fibers, whilst elaunin fibers form the subepithelial elastic layer. Fibers penetrating the thickened basement membrane of the epithelium are identified as oxytalan fibers. All three types of fibers are present throughout the lamina propria and in the submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)
BACKGROUND: Controversy still surrounds the differential susceptibility of nerve fibers to local anesthetics and its relation to selective functional deficits. In the current study we report features of conduction blockade in different classes of rat sciatic nerve fibers after injection of lidocaine by a percutaneous procedure that closely resembles clinical applications. METHODS: In 30 adult male Sprague-Dawley rats (weight, 300-400 g) during general anesthesia, impulses were recorded in different classes of sensory axons (large, Aalpha and beta fibers; small, Adelta myelinated fibers and unmyelinated C fibers) and motor axons (large, Aalpha fibers; small, Agamma myelinated fibers) classified by conduction velocity. The sciatic nerve was stimulated distally, and impulses were recorded from small filaments teased from L4-L5 dorsal (sensory) and ventral (motor) roots sectioned acutely from the spinal cord. Lidocaine at concentration of 0.05-1% was injected percutaneously in 0.1-ml solutions at the sciatic notch. Both tonic (stimulated at 0.5 Hz) and use-dependent (stimulated at 40 Hz for Adelta and Agamma fibers and at 5 Hz for C fibers) impulse inhibitions by lidocaine were assayed. RESULTS: Minimal effective (threshold) lidocaine concentrations (i.e., to block conduction in 10% of fibers) were, for sensory, 0.03% for Adelta, 0.07% for Aalphabeta, and 0.09-0.1% for C fibers, and for motor, 0.03% for Agamma and 0.05% for Aalpha fibers. The order of fiber susceptibility, ranked by concentrations that gave peak tonic fiber blockade of 50% (IC50s), was Agamma > Adelta = Aalpha > Aalphabeta > C. Faster-conducting C fibers (conduction velocity > 1 m/s) were more susceptible (IC50 = 0.13%) than slower ones (conduction velocity < 1 m/s; IC50 = 0.30%). At 1% lidocaine, all fibers were tonically blocked. Use-dependent effects accounted for only a modest potentiation of block (at a lidocaine concentration of 0.25%) in Adelta and Agamma fibers, and in C fibers phasic stimulation had even smaller effects and sometimes relieved tonic block. CONCLUSIONS: Susceptibility to lidocaine does not strictly follow the "size principle" that smaller (slower) axons are always blocked first. This order of fiber blockade is qualitatively consistent with previous reports of the order of functional deficits in the rat after percutaneous lidocaine, that is, motor = proprioception > nociception, if we assume that motor deficits first arise from conduction failure in Agamma fibers and that nociception relies on C fiber conduction.