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PubMed1978

Effect of stretch and contraction on caveolae of smooth muscle cells.

The number of caveolae present at the surface of smooth muscle cells of guinea-pig taenia coli and visualized by freeze-fracture is about 35 per micron2. (By comparison, endothelial cells of intramuscular capillaries have about 73 caveolae per micron2). The packing density of smooth muscle caveolae is not significantly different in muscle strips isotonically contracted with carbachol or stretched and relaxed in a calcium-free solution, under a range of loads varying from 1 to 15 g. Also the diameter of the fractured necks of the caveolae appears unchanged in all the experimental conditions tested. The plasma membrane of smooth muscle cells often shows a ring of intramembranous particles rimming the opening of a caveola; on the other hand, particles are rare in the membrane of the caveolae themselves. The close relation between caveolae and sarcoplasmic reticulum is readily visualized in freeze-fracture preparations. Characteristic changes of the cell surface shape accompany the contraction and relaxation of the muscle. On rare occasions small aggregates of intramembranous particles are found and it is possible that they represent punctate gap junctions. However, the characteristic clusters of particles found in the circular musculature of the caecum and ileum are not seen in taenia coli.

Animals↗
PubMed1977

Effect of contraction on lymphatic, venous, and tissue electr-lytes and metabolites in rabbit skeletal muscle.

The effect of muscle contraction on lymphatic and plasma [K+], [Na+], [Ca2+], [Mg2+], [Cl-], [Pi], [lactate] ([Lac-]); [creatine] ([Cr]), ideal osmolality (OSM), and [protein] was evaluated in femoral venous blood and lymph specimens sampled from the calf muscles of rabbits before, in the course of, and after contractions. In addition, total [K+], [Na+], [Ca2+], [Mg2+], [Cl-], and [H2O] were analyzed in the muscle tissue. To facilitate lymph sampling both hind limbs were passively flexed and extended, in imitation of natural running movements, by an electrically driven crank. The muscles of one side also performed superimposed rhythmic isotonic contractions. Before contractions, lymphatic [K+], [Na+], [Ca2+], [Mg2+], [Lac-], [Cr], and OSM did not significantly differ from corresponding femoral venous concentrations, [Cl-], and [Pi] were significantly higher, [protein] significantly lower in the lymph than in the plasma. During contractions lymphatic [K+], OSM, [Lac-], and [Pi] were raised significantly more in the lymph compared with the plasma concentrations. [Na+], [Cl-], [Ca2+], and [Mg2+] showed only small changes in the course of contractions and thereafter, and they were altered in a similar way in the lymph and plasma. It was suggested that lymphatic and interstitial concentrations were in equilibrium. Comparing inactive with active muscles, the latter lost K+ but gained Na+, Cl-, and H2O, whereas minimal changes occurred in the [Ca2+] and [Mg2+]. The changes were discussed in connection with the hypothesis that electrolyte shifts might be involved in the activation of the muscular non-proprioceptive interstitial nerve endings which appear to play a role in reflexogenic cardiovascular and respiratory control.

Animals↗
PubMed2000

Effect of quadriceps contraction on tangential patellar radiography.

This study examined whether the addition of quadriceps contraction to standard Merchant views provides additional useful information in the evaluation of patients with extensor mechanism malalignment. Fifteen patients (23 knees) with anterior knee pain due to lateral patellar compression syndrome and 22 control patients (44 knees) underwent standard Merchant views with the quadriceps relaxed and with an isometric isotonic contraction. Congruence and lateral patellar angles were measured for all groups. Although the congruence angle differed significantly between the control and symptomatic groups with the quadriceps contracted (P< or = .001), this difference also was seen without quadriceps contraction. There was also no significant difference within each group on addition of quadriceps contraction. No significant difference existed between the two groups for lateral patellar angle with quadriceps contraction. The addition of a controlled isometric quadriceps contraction did not add to the diagnostic yield of the standard Merchant view in terms of a predictable change in measured radiographic parameters.

Adult↗
PubMed1982

Urea handling by the distal tubule and collecting duct of the rat during urea--saline, isotonic saline, or urea diuresis.

The aims of the present study were to examine the effects of urea and isotonic saline loads separately and together on urea handling in the medullary collecting duct and surface distal tubules of the rat kidney. Microcatheterization of the medullary collecting duct during isotonic saline diuresis (saline at 5% of body weight per hour, plasma urea 4.3 mM/L), showed an increase in the remaining fraction of filtered urea from 56.2% at the beginning (corticomedullary junction) to 68.5% at the end (papillary tip) of the medullary collecting duct (n = 17 paired samples in six rats, p less than 0.05). There was no change in the fraction of filtered urea along the medullary collecting duct during urea diuresis (plasma urea 87 mM/L, n = 15 paired samples in six rats) or during urea--saline diuresis (plasma urea 103 mM/L, n =32 paired samples in nine rats). Micropuncture of surface distal tubules in the same animals showed an increase in the fraction of filtered urea between end-distal samples and the beginning of the medullary collecting duct from 28.9 to 56.2% during isotonic saline diuresis (p less than 0.001), and from 53.6 to 75.3% during urea--saline diuresis (p less than 0.01), but no change during urea diuresis (63.6 to 60.0%, p = NS). Our conclusions are as follows. (1) Urea entry into the medullary collecting duct during steady-state diuresis occurs at low intratubular urea contractions (isotonic saline diuresis) but not at high concentrations (urea--saline diuresis and urea diuresis). (2) Urea entry between the surface distal tubule and the beginning of the medullary collecting duct occurs during saline diuresis (isotonic saline diuresis and urea--saline diuresis) but not urea diuresis. The latter finding suggests that isotonic saline loads affect urea transport differently in juxtamedullary nephrons compared to superficial nephrons.

Animals↗
PubMed2000

Detection of fluorescently labeled actin-bound cross-bridges in actively contracting myofibrils.

Myosin subfragment 1 (S1) can be specifically modified at Lys-553 with the fluorescent probe FHS (6-[fluorescein-5(and 6)-carboxamido]hexanoic acid succinimidyl ester) (Bertrand, R., J. Derancourt, and R. Kassab. 1995. Biochemistry. 34:9500-9507), and solvent quenching of FHS-S1 with iodide has been shown to be sensitive to actin binding at low ionic strength (MacLean, Chrin, and Berger, 2000. Biophys. J. 000-000). In order to extend these results and examine the fraction of actin-bound myosin heads within the myofilament lattice during calcium activation, we have modified skeletal muscle myofibrils, mildly cross-linked with EDC (1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide) to prevent shortening, with FHS. The myosin heavy chain appears to be the predominant site of labeling, and the iodide quenching patterns are consistent with those obtained for myosin S1 in solution, suggesting that Lys-553 is indeed the primary site of FHS incorporation in skeletal muscle myofibrils. The iodide quenching results from calcium-activated FHS-myofibrils indicate that during isometric contraction 29% of the myosin heads are strongly bound to actin within the myofilament lattice at low ionic strength. These results suggest that myosin can be specifically modified with FHS in more complex and physiologically relevant preparations, allowing the real time examination of cross-bridge interactions with actin in in vitro motility assays and during isometric and isotonic contractions within single muscle fibers.

Actins↗
PubMed1991

Three-dimensional computer reconstruction of the eustachian tube and paratubal muscles.

A new method of anatomic dissection and image reconstruction using computer techniques for better understanding of eustachian tube (ET) functioning is presented. Coronal sections of two noncleft fetal skulls were photographed and projected on a graphic tablet. Contours of the pertinent structures were digitized using a mouse. Coordinates of all digitized points were entered into a special computer program. The data were transformed into three-dimensional representations of anatomic structures. The levator veli palatini muscle (M-LVP) was found to have a close relationship with the ET running underneath it and passing at the inside of the pharyngeal edge of the medial cartilage before entering the soft palate. On M-LVP contraction, this part of the medial ET cartilage appears to be the sole point of impact for ET opening. The tensor veli palatini muscle (M-TVP) is connected with the lateral cartilage of the ET and leaves the ET, rounding the pterygoid hamulus before entering the palatal aponeurosis. On this anatomic basis, action of the muscle by isotonic contraction appears to be more likely than isometric contraction.

Cartilage↗
PubMed1982

Load dependence of mammalian heart relaxation during cardiac hypertrophy and heart failure.

Mechanical properties of relaxation were studied in left ventricular rat papillary muscle during cardiac hypertrophy induced by chronic pressure and/or volume overload. Maximum velocity of isotonic lengthening was linearly related to total extent of isotonic shortening and to maximum velocity of isotonic contraction and depended on the type of chronic overloading without correlation with the degree of cardiac hypertrophy. Time to peak shortening was significantly increased in each group of hypertrophied heart muscles as compared to controls. The sensitivity of cardiac relaxation to the loading conditions was determined by the time course of relaxation. To quantify the degree of load sensitivity, we measured the ratio of isotonic area to isometric area, which was the area limited by the afterloaded force vs. time at 50% of the isometric peak tension divided by the area of the force vs. time trace in the isometric twitch below the same level of load. The value of this ratio was about 0.81 in normal rat and did not show any significant differences in hypertrophied heart muscles even at the terminal stage of congestive heart failure. During acute hypoxia the load sensitivity of relaxation disappeared both in normal and in hypertrophied hearts. Thus inadequacy in oxygen supply has more drastic effects, as compared with those induced by chronic overload, probably by affecting the sarcoplasmic reticulum uptake of activating calcium.

Animals↗
PubMed1998

Peak power output is maintained in rabbit psoas and rat soleus single muscle fibers when CTP replaces ATP.

The chemomechanical coupling mechanism in striated muscle contraction was examined by changing the nucleotide substrate from ATP to CTP. Maximum shortening velocity [extrapolation to zero force from force-velocity relation (Vmax) and slope of slack test plots (V0)], maximum isometric force (Po), power, and the curvature of the force-velocity curve [a/Po (dimensionless parameter inversely related to the curvature)] were determined during maximum Ca2+-activated isotonic contractions of fibers from fast rabbit psoas and slow rat soleus muscles by using 0.2 mM MgATP, 4 mM MgATP, 4 mM MgCTP, or 10 mM MgCTP as the nucleotide substrate. In addition to a decrease in the maximum Ca2+-activated force in both fiber types, a change from 4 mM ATP to 10 mM CTP resulted in a decrease in Vmax in psoas fibers from 3.26 to 1.87 muscle length/s. In soleus fibers, Vmax was reduced from 1.94 to 0.90 muscle length/s by this change in nucleotide. Surprisingly, peak power was unaffected in either fiber type by the change in nucleotide as the result of a three- to fourfold decrease in the curvature of the force-velocity relationship. The results are interpreted in terms of the Huxley model of muscle contraction as an increase in f1 and g1 coupled to a decrease in g2 (where f1 is the rate of cross-bridge attachment and g1 and g2 are rates of detachment) when CTP replaces ATP. This adequately accounts for the observed changes in Po, a/Po, and Vmax. However, the two-state Huxley model does not explicitly reveal the cross-bridge transitions that determine curvature of the force-velocity relationship. We hypothesize that a nucleotide-sensitive transition among strong-binding cross-bridge states following Pi release, but before the release of the nucleotide diphosphate, underlies the alterations in a/Po reported here.

Adenosine Triphosphate↗
PubMed1978

Effects of acute ethanol on the contractile state of normal and failing cat papillary muscles.

The direct effects of 100, 300 and 500 mg/100 ml ethanol on contractility of isolated, supported right ventricular papillary muscles were evaluated from 10 normal or failing cat hearts. In isometrically contracting muscles, 500 mg% ethanol decreased maximum tension in normal and failing hearts from 7.1 to 4.3 g/mm2 (P less than 0.001) and 3.4 to 2.3 (P less than 0.01) respectively, and lowered maximum tension rise from 30.4 to 20.2 g/mm2/sec (P less than 0.001) and 10.2 to 0.8 (P less than 0.01), without alterations of time to peak tension. In isotonically contracting muscles, 500 mg% ethanol reduced contractile element velocity at 0.5 g/mm2 load in normal and failing ventricles from 1.27 to 0.97 L/sec (P less than 0.001) and 0.59 to 0.39 (P less than 0.001) respectively. Thus, clinically meaningful doses of ethanol clearly, exerted dose-related negative inotropic actions on both normal and failing myocardium, thereby indicating that ethanol ingestion may exacerbate heart failure in diseased hearts.

Animals↗
PubMed1989

A comparison of the effects of denervation on the mechanical properties of rat and guinea-pig skeletal muscle.

1. A fast (extensor digitorum longus) and slow (soleus) twitch muscle were denervated in rats and guinea-pigs and isometric and isotonic contractions were followed for periods of up to 6 months after. 2. The decay of tetanic tension with time could be described as exponential. The rate of decay of tension was greatest in rat soleus and least in guinea-pig soleus by a factor of more than three. The fast muscles atrophied at intermediate rates. 3. The contraction and relaxation times of soleus and extensor digitorum longus of rat, initially prolonged by denervation, became shorter after 3 weeks. There was no such reversal in either guinea-pig muscle, indeed extensor digitorum longus twitch became even more prolonged. Guinea-pig muscles often showed signs of repetitive response to a single stimulus, resulting in distortion of relaxation of the twitch. 4. There was a slowing of isotonic shortening velocity in the late stage of denervation of guinea-pig extensor digitorum longus, accompanied by a fall in the rate of development of isometric tetanic tension. There was a just-significant (P less than 0.1) increase in the shortening velocity of rat soleus. None of the other muscles showed any change in either rate characteristic. 5. In guinea-pig extensor digitorum longus the type I fibres atrophied less than type II fibres; in all other muscles the atrophy was more uniform, possibly faster in type II. Guinea-pig soleus remained pure type I contrasting with an increase in the numbers of type II fibres in rat soleus. There was a possible increase in the number of type I fibres in guinea-pig fast muscle and no change in the rat.

Animals↗
PubMed1980

A factor analysis of twelve selected maximal isotonic strength performances on the universal gym.

This study sought to isolate and identify the underlying structure of the isotonic strength domain as exhibited on the Universal Gym. Maximal isotonic contractions were elicited from 88 college male subjects involved in a weight training program on 12 selected exercises. Factor analysis was applied to the data to delineate the underlying structure. Analysis of the raw data revealed an unclear nonrobust factor structure. However, when the variance of the anthropometric vaiables of height and weight were statistically held constant from the raw data, subsequent factor analysis of the statiscally controlled data yielded a robust three factor structure. Factor 1 was related to upper extremity and trunk isotonic strength; Factor II, lower extremity isotonic strength; Factor III, trunk and upper extremity isotonic strength. Thus, when evaluating isotonic strength responses on the Universal Gym, upper, lower extremity and trunk measures as body segments should be utilized; also, anthropometric measures of height and weight should be considered.

Body Height↗
PubMed1992

Mechanical and energetic changes in short-term volume and pressure overload of rabbit heart.

The mechanical and energetic consequences of a short-term volume overload (STVOL) hypertrophy and short-term pressure overload (STPOL) hypertrophy have been investigated in rabbits and compared with short-term sham-operated controls (STSOC). Hypertrophy was induced either by creating an aortocaval shunt (volume overload) or by banding the pulmonary artery (pressure overload). Suitable papillary muscles were excised from the hearts 8-10 days after the surgical procedure. At 27 degrees C and a stimulus frequency of 1.0 Hz, peak stress development of the STVOL preparations was significantly reduced from the control group, whereas no significant difference in peak stress development was evident between the STPOL and STSOC groups. Surprisingly, the STPOL preparations displayed pulsus alternans after only 8-10 days of inducing the overload. At steady-state conditions, the isometric 10%-90% rise times, the 90%-10% relaxation times, and the 1/2-widths were not significantly different between the treated and control groups. In isotonically contracting muscles working against a range of afterloads, the enthalpy (energy) and work output of the STVOL and STPOL preparations were depressed compared to the STSOC preparations; the differences were statistically significant for the STVOL group. Due to the parallel change in work and enthalpy, the mechanical efficiency was unaltered. A force-length-area (FLA) analysis, analogue of the pressure-volume-area (PVA) analysis, was applied to the isotonic data of this study. The isotonic enthalpy at the various load levels was plotted against the measured FLA and the data were fitted by linear regression. It was evident that the FLA correlated closely with the energy used. The STVOL and STPOL mean total energy:FLA regression lines lay parallel to but were below the STSOC line, signifying a drop in the activation heat, although this reduction did not achieve statistical significance. It is concluded that significant mechanical and energetic changes are evident after a short-term volume overload although earlier work has shown that these differences are absent at the later, compensated stage of hypertrophy. Changes associated with the pressure overload model suggest a disturbance in calcium regulation: this effect is also seen in long-term pressure overload.

Animals↗
PubMed1970

A phenomenological theory of muscular contraction. II. Generalized length variations.

In part I of this series, the theory of irreversible thermodynamics was applied to the sliding filament model to obtain rate equations for a contracting muscle at the in situ length l(o). In this paper we extend the theory to include length variations derived from the sliding filament model of contracting muscle using the work of Gordon, Huxley, and Julian (1). Accepting the validity of Hill's forcevelocity relation (2) at the in situ length, we show that Hill's equation is valid for any length provided that the values of the parameters, a, b, and V(m) vary with length as derived herein. The predicted variation with length of the velocity for a lightly loaded isotonic contraction is shown to agree well with that measured by Gordon, Huxley, and Julian (1). Chemical rates are derived as functions of length using parameters that can be obtained experimentally.

Kinetics↗
PubMed1982

Control scheme governing concurrently active human motor units during voluntary contractions.

1. The electrical activity of up to eight concurrently active motor units has been recorded from the human deltoid and first dorsal interosseous muscles. The resulting composite myoelectric signals have been decomposed into their constituent motor-unit action potential trains using a recently developed technique.2. A computer cross-correlation analysis has been performed on motor-unit firing rate and muscle-force output records obtained from both constant-force and triangular force-varying isometric contractions performed by normal subjects, and three groups of highly trained performers (long-distance swimmers, powerlifters and pianists).3. The temporal relationships between firing rate activity and force output have provided evidence that the deltoid of long-distance swimmers has a significantly higher percentage of slowly fatiguing fibres than that of normal subjects.4. Results showed that both muscles are incapable of producing a purely isotonic contraction under isometric conditions. Small, possibly compensatory force variations at 1-2 Hz result from a common drive to all active motoneurones in a single muscle pool.5. Rapid force reversals during triangular, force-varying isometric contractions appear to be accomplished through a size-related motor-unit control scheme. All firing rates decline prior to the force peak, but small motor units with slow-twitch responses tend to decrease their firing rates before large, fast-twitch motor units. This mechanism is not visually controlled, and does not depend on force rate in non-ballistic contractions.

Action Potentials↗
PubMed1980

Scalp recorded slow potential shifts during isometric ramp and hold contractions in human subjects.

During voluntary isometric slow ramp contractions of the hand up to an internally defined target force level sustained negative potential shifts in the EEG were recorded from 6 human subjects. The potential shifts are composed of (a) a bilateral wide spread negativity with a maximum amplitude at the vertex, and (b) a smaller negative wave contralateral to the responding hand with a maximum over the respective motor area. Both components disappear during a voluntary isometric isotonic contraction when subjects have to maintain a stable force level for some seconds.

Action Potentials↗
PubMed1986

Influence of plating density on individual cell growth, cell division and differentiation of neonatal rat heart primary cultures.

The influence of plating cell density of an originally enriched myocardial cell population has been studied in neonatal rat heart cells in culture. Low density (LDM) is defined as a density (24 h after plating) of 209 +/- 44 cells/mm2 (mean +/- SEM) and is compared with high density (HDM), 419 +/- 67 cells/mm2. Cell growth is evaluated by the total cell number, the percentage of myocardial cells (M) in culture (PAS method) and the protein content per cell. Some differentiation parameters such as beating rates, glycogen concentration, enzymatic activities (cytochrome C oxidase and glycogen phosphorylase) are studied with time in culture (48, 96 and 192 hr). High density was designed to yield a complete confluency of the cells within 24 hr after plating and to minimize cell division of the non-muscle cells (F). At high density, cell division of F cells is effectively limited, thus leading to a more stable model regarding the cell density per plate and the percentage of M cells: 85.7 +/- 4% and 33.4 +/- 6% in LDM cultures compared with 86.5 +/- 4.7% and 51.7 +/- 9.8% in HDM cultures at 24 and 192 hr (mean +/- SEM). Heart cells increase similarly in size with age in culture in both groups. In HDM cultures the spontaneous contractions begin sooner (24 hr) than in LDM cultures and are more rapidly synchronized. The beating rate is higher in HDM cultures between 48 and 96 hr; however, after this time it falls in HDM and does not fall in LDM. Thus the overgrowth of muscle cells by non-muscle cells is not responsible for loss of beating with time in culture but more likely high density could be a limiting factor for isotonic contraction. There is more glycogen per myocyte in LDM than in HDM cultures. The cell density influences the enzymatic activities of cytochrome C oxidase and glycogen phosphorylase. The cytochrome oxidase activity is higher in HDM cultures than in LDM cultures at 96 hr whereas glycogen phosphorylase activity is higher in LDM cultures at time 96 and 192 hr. In LDM cultures, the ratio cytochrome C oxidase/glycogen phosphorylase decreases with time in culture from 1.685 +/- 0.680 at 48 hr to 0.780 +/- 0.290 at 192 hr but not in HDM cultures (2.13 +/- 0.36 and 1.64 +/- 0.34 respectively). Thus plating density influences properties of heart cell cultures with regard to the overgrowth of the F-cell population and the differentiated state of M cells.

Aminosalicylic Acid↗
PubMed1988

Dynamic organization of Physarum plasmodium.

Birefringent fibrils (BRFs) with a positive sign composed of bundles of F-actin were found throughout the Physarum plasmodium with the mode of existence differing regionally. In the zone behind the leading edge of an advancing plasmodium, where cytoplasmic sol and gel were still not well differentiated, more BRFs came to the foreground when the endoplasm flowed backward (emptying phase), and a substantial portion disappeared when the endoplasm flowed forward (filling phase), except for nodes, from which BRFs were reorganized in the early emptying phase of each cycle. BRFs found in the wall of the streaming channel in the posterior network and the branched vein section ran in parallel to or helically around the channel. They were much more stable and maintained strong birefringence irrespective of the direction of the cytoplasmic flow. When the fan-like expanse ceased moving forward, the BRFs no longer appeared and disappeared cyclically but persisted in the area which had previously been the front. We concluded that the site of the active contraction-relaxation rhythm in an advancing plasmodium with antero-posterior polarity is restricted to its frontal zone and that the rest of the plasmodium is in a state of "tonus" which continuously imparts a certain level of hydrostatic pressure to the interior. The meaning of the tonus and the mechanics of tensile force production in the plasmodium are discussed in terms of a working hypothesis arrived at from the phase relationship between isometric and isotonic contraction waves.

Birefringence↗
PubMed1976

[Pharmacological Properties of Fendiline in Cardiac and Smooth Muscle (author's transl)].

The pharmacological properties of fendiline N-(1-phenylethyl [1])-3,3 - diphenylpropylamine-hydrochloride; Sensit, were investigated in the isolated guinea pig heart and in isolated circular smooth muscle strips of bovine coronary arteries, pulmonary arteries and trachea. 1. Fendiline dose dependently increased coronary flow by up to 200% but, different from verapamil, did not inhibit contraction. 2. Fendiline dose dependently relaxed coronary strips and, more powerfully, tracheal and pulmonary arterial strips. 3. In cardiac muscle, fendiline was almost completely retained for a prolonged period of time. In the smooth muscle tissues under study, fendiline accumulated twenty-fold above the concentration present in the organ bath. 4. In paced hearts, fendiline non-competitively inhibited the positive inotropic effect of isoprenaline in doses that did not significantly depress the amplitude of isotonic contractions. 5. In the guinea pig heart, adenosine uptake becomes progressively inhibited when coronary flow increases. This "washout" effect was definitely counteracted by fendiline and by NaNO2, but was augmented by papaverine, hexobendine and dipyridamol. The counteraction of the "washout effect" by fendiline as well as by NaNO2 is most likely due to the opening of additional (previously closed) capillaries.

Adenosine↗