Biomedical subjects

A Maier

Publications and source records attributed to A Maier.

At least 91 records · Page 5Linked to original sources

PubMed1997

Development and regeneration of muscle spindles in mammals and birds.

The morphological and physiological development of avian and mammalian muscle spindles is reviewed, with emphasis on the recent literature. Subjects covered include the effect of sensory innervation and growth factors on the induction of muscle spindles, genesis of intrafusal fiber types as defined by isoforms of myosin heavy chains, and the establishment of the outer spindle capsule. Because of its relevance to normal development, degeneration and regeneration are also treated. Similarities and differences between mammalian and avian muscle spindle formation are discussed.

Animals↗

PubMed1996

Low affinity of Trypanosoma brucei transferrin receptor to apotransferrin at pH 5 explains the fate of the ligand during endocytosis.

Uptake of host transferrin (Tf) in Trypanosoma brucei is mediated by a heterodimeric, glycosyl-phosphatidylinositol-anchored receptor. After endocytosis, Tf is delivered to lysosomes where it is proteolytically degraded. So far, the sequence of events leading to ligand dissociation and degradation is undefined. We now show by Triton X-114 phase separation that iron-free Tf (apo-Tf) dissociates from the receptor at pH 5.0. The low affinity of apo-Tf for its receptor at pH 5.0 is confirmed by an apparent dissociation constant of 1.1 microM. The implications of this result on the mechanism of intracellular processing of Tf in trypanosomes are discussed.

Animals↗

PubMed1996

Immunochemiluminometric assay with two monoclonal antibodies against the N-terminal sequence of human parathyroid hormone.

We have developed an immunochemiluminometric assay (ICMA) with two monoclonal antibodies for the N-terminal sequence of human parathyroid hormone (hPTH). One monoclonal antibody (A1-70) was physically adsorbed onto polystyrene beads, the other (B1-70) was labelled with acridinium ester and synthetic hPTH (1-38) was used as standard. This assay has cross-reactions with synthetic hPTH (1-34) and hPTH (1-84) but no cross-reactions with hPTH (4-16), (28-48), (39-84), (44-68), (53-84) and hPTH-rP (1-86). The assay detection limit is 0.4 pmol/l. The normal range is 1.3-12 pmol/l based on 72 normal volunteers. About 91% of study patients (n = 58) with surgically proven primary hyperparathyroidism (1 degree HPT) had PTH values above normal and one of them showed a low normal intact PTH value but elevated PTH values with use of this assay. After immunoabsorption of plasma samples from patients with secondary hyperparathyroidism (2 degrees HPT) on hemodialysis with polystyrene beads containing antibodies against hPTH (39-84), some patients still showed significant amounts of PTH in this new ICMA but not intact PTH. The data reveal that significant amounts of amino-terminal immunoreactive PTH fragments rarely exist in 1 degree HPT but are present in some patients with 2 degrees HPT. The major advantage of this assay is to measure both amino-terminal PTH fragments and intact PTH with no interference from carboxy-terminal PTH fragments because two anti-N-terminal hormone sequence monoclonal antibodies are used.

Adult↗

PubMed1996

Extracellular matrix and transmembrane linkages at the termination of intrafusal fibers and the outer capsule in chicken muscle spindles.

Attachments of intrafusal fibers and of the outer spindle capsule at the far polar region were examined by immunohistochemistry in serially sectioned chicken leg muscles. Patterns of distribution of connective tissues and intracellular filaments suggest that, in this segment of the muscle spindle, intrafusal fibers bind laterally with the capsule. Contrary to extrafusal fibers at myotendinous junctions, folded plasmalemmas at the ends of intrafusal fibers were rare. Thus, there was little end-to-end interlocking between intrafusal fibers and the extracellular matrix. The tapered contours of terminating intrafusal fibers resembled those of extrafusal fibers which end in fascicles without tendinous connections. At points where the distal portions of intrafusal fibers closely adjoined and overlapped extrafusal fibers, alpha-actinin, vinculin, filamin, talin, beta 1 integrin, spectrin, and dystrophin occurred with moderate to great frequency. It is generally accepted that these compounds are links in molecular chains that extend from the intracellular space across cell membranes to the extracellular matrix. Their location along substantial lengths of extrafusal fibers, distal capsule, and terminating intrafusal fibers suggests the presence of numerous transverse connections between elements of the terminal portion of the spindle and nonspindle tissues. Hence, it is likely that forces monitored by chicken spindles in muscles undergoing length changes are transferred from extrafusal fibers and extracellular matrix to the receptors in large part via lateral shear instead of by longitudinal tension.

Animals↗

PubMed1996

N-[4-hydroxyphenyl] retinamide in rheumatoid arthritis: a pilot study.

OBJECTIVE: To evaluate the efficacy and tolerability of N-[4 hydroxyphenyl] retinamide (4-HPR), a synthetic retinoid, in the treatment of rheumatoid arthritis (RA). METHODS: An uncontrolled, open clinical trial with synovial biopsy pre- and postmedication to evaluate the clinical effects of 4-HPR as well as its effects on metalloproteinase gene expression. RESULTS: Twelve patients with severe, longstanding RA were enrolled in this study. Six patients withdrew before study completion, 2 because of drug toxicity, 2 because of a flare of RA, and 2 because of intercurrent medical problems. No patient met predetermined Paulus criteria treatment response, and there was no improvement in the laboratory parameters, except for a modest decrease in C-reactive protein. No decrease in messenger RNA for the metalloproteinases collagenase and stromelysin was seen in the 2 patients in whom paired synovial biopsies were obtained. CONCLUSION: No beneficial clinical effect was observed with the retinoid 4-HPR in the treatment of severe, longstanding RA at the 300 mg/day dosage studied. The use of higher dosages is precluded by the observed toxicities. The effect of this drug in patients with early or mild disease was not studied. Although this particular retinoid was not effective in this pilot study, the use of other retinoids in RA should still be considered.

Antineoplastic Agents↗

PubMed1996

Beta 1D integrin displaces the beta 1A isoform in striated muscles: localization at junctional structures and signaling potential in nonmuscle cells.

The cytoplasmic domains of integrins provide attachment of these extracellular matrix receptors to the cytoskeleton and play a critical role in integrin-mediated signal transduction. In this report we describe the identification, expression, localization, and initial functional characterization of a novel form of beta 1 integrin, termed beta 1D. This isoform contains a unique alternatively spliced cytoplasmic domain of 50 amino acids, with the last 24 amino acids encoded by an additional exon. Of these 24 amino acids, 11 are conserved when compared to the beta 1A isoform, but 13 are unique (Zhidkova, N. I., A. M. Belkin, and R. Mayne. 1995. Biochem. Biophys. Res. Commun. 214:279-285; van der Flier, A., I. Kuikman, C. Baudoin, R, van der Neuf, and A. Sonnenberg. 1995. FEBS Lett. 369:340-344). Using an anti-peptide antibody against the beta 1D integrin subunit, we demonstrated that the beta 1D isoform is synthesized only in skeletal and cardiac muscles, while very low amounts of beta 1A were detected by immunoblot in striated muscles. Whereas beta 1A could not be detected in adult skeletal muscle fibers and cardiomyocytes by immunofluorescence, beta 1D was localized to the sarcolemma of both cell types. In skeletal muscle, beta 1D was concentrated in costameres, myotendinous, and neuromuscular junctions. In cardiac muscle this beta 1 isoform was found in costamers and intercalated discs. beta 1D was associated with alpha 7A and alpha 7B in adult skeletal muscle. In cardiomyocytes of adult heart, alpha 7B was the major partner for the beta 1D isoform. beta 1D could not be detected in proliferating C2C12 myoblasts, but it appeared immediately after myoblast fusion and its amount continued to rise during myotube growth and maturation. In contrast, expression of the beta 1A isoform was downregulated during myodifferentiation in culture and it was completely displaced by beta 1D in mature differentiated myotubes. We also analyzed some functional properties of the beta 1D integrin subunit. Expression of human beta 1D in CHO cells led to its localization at focal adhesions. Clustering of this integrin isoform on the cell surface stimulated tyrosine phosphorylation of pp125FAK (focal adhesion kinase) and caused transient activation of mitogen-activated protein (MAP) kinases. These data indicate that beta 1D and beta 1A integrin isoforms are functionally similar with regard to integrin-mediated signaling.

Amino Acid Sequence↗

PubMed1996

Expression and function of receptors for extracellular matrix proteins in human ductal adenocarcinomas of the pancreas.

Extracellular matrix proteins (ECM) may influence cellular differentiation via their receptors, the integrins. We recently presented evidence that ductal adenocarcinomas of the pancreas are able to produce ECM in vitro and in vivo (Br J Cancer 1994;49:144-51). This study examines whether pancreatic carcinoma cells are able to interact with ECM by expressing functionally active integrins. In eight human pancreatic tumor cell lines (AsPC-1, BxPC-3, CAPAN-1 and -2, PANC, PaTu-2, -3, and -44) and six xenografted tumors RNA and protein expression of integrin subunits alpha 5 (fibronectin receptor), alpha 6 (laminin receptor), and alpha V (vitronectin receptor) was investigated. In addition, alpha 1-alpha 6 and alpha V as well as beta 1-beta 4 were studied by fluorescence-activated cell sorter analysis. Integrin function was tested by attachment assays. alpha 2, alpha 3, alpha 5, alpha 6, and alpha V as well as beta 1, beta 3, and beta 4 were expressed, at both the RNA and the protein level, by all pancreatic tumors in vitro and in vivo. The tumor cell lines showed dose dependent adhesion to collagen, fibronectin, and laminin. Integrin expression could be modulated in part by serum depletion. None of the tumors showed alpha 1, alpha 4, and beta 2. Tumor cell differentiation or production of ECM was not correlated with integrin expression. Pancreatic ductal adenocarcinomas express a certain pattern of functionally active integrins that enable interaction with most matrix proteins, e.g., collagen, fibronectin, and laminin. Pancreatic adenocarcinomas possess both the ligands and the receptors of the extracellular matrix network. We speculate that through both classes of molecules, the tumor cells may bind to fibroblasts and probably stimulate their growth. However, it remains unclear whether and how integrin-ECM interaction exerts an influence on tumor cell differentiation.

Animals↗

PubMed1996

Polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs and related environmental compounds: biological markers of exposure and effects.

Lung cancer caused by polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs and related environmental agents is a major problem in industrialized nations. The high case-fatality rate of the disease, even with the best supportive treatment, underscores the importance of primary lung cancer prevention. Development of biomarkers of exposure and effects to PAHs and related compounds is now underway and includes measurement of urinary metabolites of specific PAHs as well as detection of protein and DNA adducts as indicators of effective dose. Validation of these markers in terms of total environmental dose requires that concurrent measures of air levels and potential dermal exposure be made. In addition, the interrelationships between PAH biomarkers must be determined, particularly when levels of the marker in surrogate molecules (e.g., protein) or markers from surrogate tissues (e.g., lymphocyte DNA) are used to assess the risk to the target organ, the lung. Two approaches to biomarker studies will be reviewed in this article: the progress made using blood lymphocytes as surrogates for lung tissues and the progress made developing noninvasive markers of carcinogen-DNA adduct levels in lung-derived cells available in bronchial-alveolar lavage and in sputum. Data are presented from studies in which exfoliated urothelial cells were used as a surrogate tissue to assess exposure to human urinary bladder carcinogens in occupational groups.

Biomarkers↗

PubMed1995

Basal lamina development in chicken muscle spindles.

The development of basal laminas was examined in immunohistochemical sections of chicken leg muscle spindles from embryonic day (E) 13 to 8 weeks postnatal. Fragments of basal laminas as seen with immunostaining for isoforms of laminin were already observed in E6 muscles. When clusters of intrafusal myotubes were first recognized at E13-14, they were surrounded by basal laminas which were incomplete both in terms of coverage and molecular composition. More mature basal lamina tubes individually enclosed young myofibers at E18. After afferents made contact with myotubes, synaptic portions of basal laminas at myosensory junctions reacted strongly with antibodies against s-laminin and chondroitin sulfate proteoglycan, while extrasynaptic portions were negative or reacted only weakly. At synaptic basal laminas of neuromuscular junctions heparin sulfate proteoglycan and s-laminin became prominent after E16. Contrary to the early presence of basal lamina proteins around intrafusal fibers, initial deposition of basal lamina proteins in the outer spindle capsule was not recognized until E17-18, and significant amounts were not detected until postnatal week 1. Unlike intrafusal basal laminas, capsular basal laminas developed no distinct specialized regions; however, molecular compositions of intrafusal and capsular basal laminas were similar.

Animals↗

PubMed1995

Fiber-type compositions in postnatal chicken muscle spindles with low intrafusal fiber counts and their developmental significance.

The fiber-type composition of postnatal chicken leg muscle spindles with from one to four intrafusal fibers was examined in sections incubated with monoclonal antibodies against fast and slow myosin heavy chains. In monofibral spindles the lone intrafusal fiber was almost always fast. In duofibral spindles usually one slow and one fast fiber were present. Trifibral spindles most often displayed two fast and one slow fiber, whereas quadrofibral receptors characteristically contained two slow and two fast fibers. Earlier results showed that the primary intrafusal myotube in nascent spindles has almost always a fast myosin heavy chain profile and that the proportion of slow myotubes and fibers increases as intrafusal fiber bundles grow in size. Data from postnatal chicken leg muscles collected here suggest that up to the first four fibers this proportional increase can be largely accounted for if consecutive intrafusal fibers arise in a fast-slow-fast-slow sequence. The late recognition during myogenesis of primary intrafusal myotubes and their fast myosin heavy chain profiles warrant exploring if nascent chicken muscles spindles are first seeded by fast fetal myoblasts.

Animals↗

PubMed1995

Nasal cancer in leather workers: an occupational disease.

Nasal cancer has a number of causative agents; exposures to most of the established nasal carcinogens occur in the workplace. An increased risk of nasal cancer has been ascertained in shoe-making and shoe-repairing, but the results for leather goods manufacture and leather tanning don't provide adequate evidence of carcinogenicity. Findings from two epidemiological studies carried out in Italy (a case/control study and a case/series report) add further information on this issue. The case/control study was performed in the provinces of Siena (Tuscany), Verona and Vicenza (Venetia) including 96 cases and 378 controls. A significant increased risk (Odds Ratio: 6.8; 90% C.I. = 1.9-25) of sinonasal cancer was found for the employ in the whole leather industry; Odds Ratio of 8.3 (C.I. = 1.9-36) and 5.0 (C.I. = 0.92-28) were associated with shoe-making and leather tanning. The case/series report is based on 110 patients accepted in some Italian hospitals during last three years (1990-1993): 26 cases had worked in the leather industry; adenocarcinoma is the most frequent type observed. Chromium salts and natural tannins are indicated as possible aetiological agents.

Case-Control Studies↗

PubMed1995

Biliary sludge after liver transplantation: 2. Treatment with interventional techniques versus surgery and/or oral chemolysis.

OBJECTIVE: Interventional treatment of biliary sludge in liver transplant recipients includes transhepatic biliary drainage and saline irrigation, catheter chemolysis and/or basket extraction, and endoscopic intervention. The purpose of this study was to compare these interventional procedures with oral chemolysis and with surgical treatment of biliary sludge in order to evaluate the effectiveness of interventional procedures as an alternative to surgery in the treatment of this complication. MATERIALS AND METHODS: We retrospectively evaluated the outcome of several forms of treatment for biliary sludge occurring after liver transplantation in 49 cases. Treatments included oral chemolysis with chenodeoxycholic acid (n = 35), percutaneous transhepatic biliary drainage (n = 13) followed by irrigation with heparinized saline solution (n = 4), intraluminal chemolysis with glycero-octanoate-carnosine and bile salts-EDTA (n = 3) and/or basket extraction (n = 5), and endoscopic intervention (n = 2) or surgery (n = 26). Oral chemolysis was attempted in all cases of biliary sludge if no other complications were present. If this conservative treatment failed and the sludge was limited to the main bile ducts, interventional procedures were attempted. Surgical removal of the sludge (n = 15) or retransplantation (n = 5) without any attempt at prior nonsurgical treatment was performed if concomitant complications were present (n = 14) or if the extent of the sludge was considered too time-consuming for an interventional attempt (n = 6). The six patients in whom nonsurgical treatment failed underwent surgery. Treatment was considered successful if cholangiograms obtained after therapy showed no more evidence of sludge. Treatment was considered a failure if biliary sludge was shown after therapy by means of cholangiography, surgery, or autopsy. RESULTS: Complete disappearance of biliary sludge as a result of oral chemolysis was achieved in 14 (40%) of 35 cases. Interventional procedures were performed in 15 of the patients in whom oral treatment failed. After percutaneous transhepatic biliary drainage, the sludge was successfully removed by chemolysis with glycero-octanoate-carnosine in three cases, by basket extraction in one case, and by a combination of chemolysis and basket extraction in three cases. In two other cases, underlying recurrent tumor was treated palliatively with percutaneous transhepatic biliary drainage or endoscopic stenting. Irrigation with heparinized saline solution failed in four cases, and percutaneous or endoscopic basket extraction failed in one case each. Surgical treatment was successful in 18 (86%) of 21 cases, and retransplantation was successfully done in five patients. In all, interventional techniques were used in 43% of the patients with biliary sludge who could not be treated successfully with oral chemolysis, and the overall success rate was 60%. CONCLUSION: Interventional techniques are effective therapeutic alternatives for treating biliary sludge occurring after liver transplantation and should be considered before surgical procedures. An indication for interventional procedures in biliary sludge is lack of success of oral chemolysis and an absence of other complications that require surgery or retransplantation.

Adolescent↗

PubMed1995

Biliary sludge after liver transplantation: 1. Imaging findings and efficacy of various imaging procedures.

OBJECTIVE: Biliary sludge (inspissated, thickened bile or collective collagen tissue from destroyed [or necrotic] bile duct walls) can be found a few days to several years after liver transplantation, mainly in the common and main hepatic bile ducts. The purpose of this study was to review the imaging findings of biliary sludge occurring after liver transplantation and to determine the relative merits of various imaging procedures (cholangiography, CT, and sonography) for establishing the diagnosis. MATERIALS AND METHODS: Cholangiograms, sonograms, and CT scans obtained in 352 patients with 400 liver transplants were reviewed retrospectively for evidence of biliary sludge. In all patients, T-tube cholangiograms were routinely obtained 7 and 30 days and 3 months after transplantation. Thereafter, in the absence of findings, the T-tube was removed. In all patients, sonograms were obtained immediately, 2 and 7 days after transplantation. Additional cholangiograms were obtained when biliary complications were suspected (T-tube cholangiograms in 215 patients, percutaneous transhepatic cholangiograms in 79 patients, and endoscopic retrograde cholangiograms in five patients after T-tube removal). Additional sonograms were obtained in 289 patients and CT scans in 238 patients when complications were suspected. The findings of these various imaging studies were analyzed and compared with each other, with the clinical course of the patient, and with surgical and histologic findings to determine the relative merits of each imaging method for the diagnosis of biliary sludge. Criteria for the diagnosis of biliary sludge were filling defects or pluglike obstruction seen on cholangiograms or material filling the bile ducts seen on sonograms or CT scans. The radiologic diagnosis of biliary sludge was certified by gross specimens obtained at surgery (n = 21) or autopsy (n = 2) or by complete disappearance of the radiologic findings with specific oral or interventional treatment (n = 28). RESULTS: Biliary sludge was diagnosed on the basis of radiologic findings in 51 (13%) of 400 transplanted livers. Cholangiograms (T-tube in 34, percutaneous transhepatic cholangiography in seven, a combination of T-tube and percutaneous transhepatic cholangiography in eight, and a combination of endoscopic retrograde and percutaneous transhepatic cholangiography in two cases) showed biliary sludge in all 51 cases. Cholangiographic findings included filling defects in 34 (67%) and obstruction of the bile duct with pluglike appearance in 17 (33%) of the 51 cases. Dilatation of bile ducts was present in 32 (63%) of the 51 cases. The presence of biliary sludge was certified in 50 of these cases, with one case turning out to be a sutural granuloma at autopsy. On sonograms, biliary sludge was shown as echogenic material in the main bile ducts in only 16 (31%) of the 51 cases, with dilatation of bile ducts in 12 of them. In 10 others (20%), sonograms showed dilatation of the bile ducts but did not show the sludge itself. CT scans did not show the sludge in any of the 12 cases in which they were obtained. CONCLUSION: Our results show that cholangiography is the only accurate imaging method for diagnosing biliary sludge after liver transplantation. Sonography is limited and CT is of no value for this purpose. In the absence of a T-tube, endoscopic retrograde or percutaneous transhepatic cholangiography should be used. Otherwise, T-tube cholangiography is the method of choice. Filling defects and obstruction of the bile ducts with pluglike material are characteristic findings of biliary sludge seen on cholangiograms.

Adolescent↗

PubMed1995

Lacking effect of grapefruit juice on theophylline pharmacokinetics.

Grapefruit juice inhibits the biotransformation of several drugs, including caffeine (23% clearance reduction), which is metabolized by the cytochrome P450 isoform CYP1A2. Since CYP1A2 also participates in theophylline biotransformation, a randomized change-over study on a possible interaction between grapefruit juice and theophylline was conducted. Twelve healthy young male nonsmokers were included (median 26 (range 23-30) years, weight 73 (65-85) kg). Theophylline was given as a single dose of 200 mg in solution (Euphyllin 200), diluted by 100 ml of either water or grapefruit juice (751 mg/l naringin). Subsequently, additional fractionated 0.91 of water or juice were administered until 16 hours postdose. Theophylline concentrations in plasma withdrawn up to 24 hours postdose were measured by HPLC, and its pharmacokinetics were estimated using compartment model independent methods. To compare between the 2 treatments, ANOVA based point estimates and 90% confidence intervals (given in parentheses) were calculated for the test (= grapefruit coadministration) to reference (= water coadministration) ratios (Tmax: differences). These were: Cmax 0.90 (0.81-1.00), AUC 1.02 (0.95-1.11), Cmax/AUC 0.88 (0.81-0.95), T 1/2el 1.03 (0.98-1.09), Tmax 0.15 h (-0.11h-0.41 h). Thus, no pharmacokinetic interaction between grapefruit juice and theophylline was observed. This finding is in contrast to the effect of grapefruit juice reported on caffeine metabolism and may be due to the contribution of enzymes other than CYP1A2 to primary theophylline metabolism or to differences in naringin and/or naringenin kinetics between studies.

Absorption↗

PubMed1994

Type and regional diversity in the distribution of myosin heavy chains in chicken intrafusal muscle fibers.

BACKGROUND: Chicken intrafusal fibers were classified on the basis of their myosin heavy chain (MHC) composition, which was compared to that of mammalian nuclear bag and nuclear chain types. METHODS: Immunoreactivities of intrafusal fibers from leg muscles of 8-week-old chickens were evaluated in serial cross-sections after incubation with monoclonal antibodies against slow-twitch, slow-tonic, or fast-twitch MHC and fast muscle C-protein. RESULTS: Four categories of slow intrafusal fiber could be distinguished on the basis of differential expression of slow-twitch and slow-tonic MHC. Segregation into types was most evident at the motor axon supplied pole, followed by the sensory region of the equator. Fiber types were least distinct at the juxtaequator where sensory and motor axons meet. Intrafusal fibers negative for slow myosins reacted with anti-fast myosins. Fast fibers were best viewed as a single group without subdivisions. Immunostaining for fast muscle C-protein paralleled in large part reactivities for neonatal/fast MHC, indicating that proteins other than MHC are useful fiber type markers. CONCLUSIONS: Despite regional changes along the length of intrafusal fibers and some variation within fiber types, the concept of separate MHC-based fiber types was valid as long as typing of fibers was restricted to the proximal polar region. Comparisons of MHC profiles revealed similarities between chicken fast intrafusal fibers and mammalian nuclear chain fibers and between some chicken slow intrafusal fibers and mammalian nuclear bag fibers.

Animals↗

PubMed1994

Fibrillin and elastin networks in extrafusal tissue and muscle spindles of bovine extraocular muscles.

PURPOSE: Bovine extraocular rectus muscles were examined to map the distribution of elastin and fibrillin in extrafusal tissue and muscle spindles. METHODS: Immunohistochemical techniques and immunolocalization were employed to pin-point the placement of molecules relative to muscle fibers. RESULTS: Strands containing elastin and fibrillin surrounded all extrafusal fibers. They also covered the external surface of intrafusal fibers, more extensively at the equator than at the pole. Within strands elastin was placed in the center, whereas fibrillin was located in microfibrils on the periphery. CONCLUSIONS: The wide distribution in extrafusal tissue of elastin and fibrillin suggests that they are factors in determining the mechanical properties of extraocular muscles. Their placement in proximity to individual intrafusal fibers should affect the viscoelastic properties of these fibers and, thus, influence the dimensions of the afferent discharge.

Animals↗

PubMed1993

Regional differences in organization of the extracellular matrix and cytoskeleton at the equator of chicken intrafusal muscle fibres.

Equatorial regions of chicken intrafusal fibres were examined with a panel of monoclonal antibodies against intracellular proteins and components of extracellular matrix to identify structural associations at points of contact between sensory terminals and intrafusal fibres, and at points which lacked them. One aspect of this study was to establish whether the known morphological differences between myosensory and neuromuscular junctions also extended to the molecular level. As viewed in cross-sections, myosensory junctions at the equator are restricted to approximately one-half of the intrafusal fibre circumference, a region referred to as the sensory sector. The diametrically opposite region which lacks sensory terminals is referred to as the non-sensory sector. The basal lamina over the sensory sector was positive for chondroitin sulphate, while that part which covered the non-sensory sector was negative. Staining for collagen type IV was very faint at the sensory sector and stronger at the non-sensory sector, but immunoreactivity for heparan sulphate proteoglycan and laminin was moderate to strong in all parts of the basal lamina. Within intrafusal fibres, filamin and alpha-actinin were largely limited to the sensory sector. The major feature of the non-sensory sector was a sharply delineated, narrow intrafibre crescent of vinculin, and colocalized with it, a crescent of talin. The plasmalemma of intrafusal fibres at the non-sensory sector reacted positively for the beta 1 subunit of the integrin family of receptors. Immunolocalization of these receptors was not observed to any significant extent in the sensory sector. Towards the end of the equator and the initial portion of the juxtaequator, chondroitin sulphate, vinculin and the other proteins came gradually to be distributed equally all the way round the intrafusal fibres. This changeover in distribution of connective tissue proteins and structural intracellular proteins parallels the decreasing number of contacts made by sensory terminals.

Animals↗

PubMed1993

Transient expression of a ventricular myosin heavy chain isoform in developing chicken intrafusal muscle fibers.

Sections of chicken tibialis anterior and extensor digitorium longus muscles were incubated with monoclonal antibodies against myosin heavy chains (MHC). Ventricular myosin was present in developing secondary intrafusal myotubes when they were first recognized at embryonic days (E) 13-14, and in developing extrafusal fibers prior to that date. The reaction in intrafusal fibers began to fade at E17, and in 2-week-old postnatal and older muscles the isoform was no longer recognized. Only those intrafusal fibers which also reacted with a monoclonal antibody against atrial and slow myosin contained ventricular MHC. Intrafusal myotubes which developed into fast fibers did not express the isoform. Hence, based on the presence or absence of ventricular MHC, two lineages of intrafusal fiber are evident early in development. Strong immunostaining for ventricular MHC was observed in primary extrafusal myotubes at E10, but the isoform was already downregulated at E14, when secondary intrafusal myotubes were still forming and expressed ventricular MHC. Only light to moderate and transient immunostaining was observed in coexisting secondary extrafusal myotubes, most of which developed into fast fibers. Thus at the time when nascent muscle spindles are first recognized, differences in MHC profiles already exist between prospective intrafusal and extrafusal fibers. If intrafusal fibers stem from a pool of primordial muscle cells, which is common to intrafusal and extrafusal myotubes, they diverged from it some time prior to E13.

Animals↗