High Myosin ATPase Activity Research Articles

Contractile and biochemical properties of rat soleus and plantaris after hindlimb suspension

This study examined the relationship between contractile and isomyosin changes occurring in rat soleus (SOL) and plantaris (PLAN) muscles after 28 days of hindlimb suspension. SOL muscles from suspended animals exhibited a 45% decline in muscle weight compared with controls (P less than 0.05) accompanied by a 49% decrease in peak twitch tension (Pt) and a 59% reduction in peak tetanic tension (Po). Smaller reductions were observed in muscle weight, Pt, and Po (12, 43, and 24%, respectively) for the suspended PLAN. Maximal shortening velocity (Vmax) of the suspended SOL and the velocity of unloaded shortening were increased by 36 and 35%, respectively, but there was no suspension-induced change in PLAN Vmax. Suspension induced a 22% increase in SOL myosin adenosinetriphosphatase (ATPase) activity that was accompanied by a shift in the native myosin isoform distribution characterized by an increase in the relative amounts of intermediate and fast myosin. The more modest changes in the contractile function of suspended PLAN were accompanied by a small (7%) increase in myosin ATPase activity but no significant changes in myosin isoform distribution. The results of this study confirm that hindlimb suspension results in significant speeding of SOL contractile properties and suggest that the shift toward faster myosin isoforms with a higher myosin ATPase activity likely accounts for these mechanical changes.

Biochemical basis of thyroid hormone action in the heart

Thyroid hormone-induced changes in cardiac function have been recognized for over 150 years; however, the biochemical basis of triiodothyronine (T 3) action in the heart has been intensely investigated only during the last two decades. T 3-induced changes in cardiac function can result from direct or indirect T 3 effects. Direct T 3 effects result from T 3 action in the heart itself and are mediated by nuclear or extranuclear mechanisms. Extranuclear T 3 effects, which occur independent of nuclear T 3 receptor binding and increases in protein synthesis, influence primarily the transport of amino acids, sugars, and calcium across the cell membrane. Nuclear T 3 effects are mediated by the binding of T 3 to specific nuclear receptor proteins, which results in increased transcription of T 3-responsive cardiac genes. The T 3 receptor is a member of the ligand-activated transcription factor family and is encoded by cellular erythroblastosis A (c- erb A) genes. The c- erb A protein is the cellular homologue of the viral erythroblastosis A (v- erb A) protein, which causes red cell leukemia in chickens. Currently, three T 3-binding isoforms of the c- erb protein and two non-T 3-binding nuclear proteins that exert positive and negative effects on T 3-responsive cardiac genes have been identified. T 3 increases the heart transcription of the myosin heavy chain (MHC) α gene and decreases the transcription of the MHC β gene, leading to an increase of myosin V 1 and a decrease in myosin V 3 isoenzymes. Myosin V 1, which is composed of two MHC α, has a higher myosin ATPase activity than myosin V 3, which contains two MHC β. The globular head of myosin V 1, with its higher ATPase activity, leads to a more rapid movement of the globular head of myosin along the thin filament, resulting in an increased velocity of contraction. T 3 also leads to an increase in the speed of diastolic relaxation, which is caused by the more efficient pumping of the calcium ATPase of the sarcoplasmic reticulum (SR). This T 3 effect results from T 3-induced increases in the level of the mRNA coding for the SR calcium ATPase protein, leading to an increased number of calcium ATPase pump units in the SR. Overall, thyroid hormone leads to an increase in ATP consumption in the heart. In addition, less chemical energy of ATP is used for contractile purposes and more of it goes toward heat production, which causes a decreased efficiency of the contractile process in the hyperthyroid heart.

The higher myosin ATPase activity in the right heart ventricle of the rat, proved by histophotometry

Comparing the myosin-ATPase activity in the left and right ventricular wall of the hearts from 6 rats by scanning histophotometry, a higher enzyme activity in the right ventricle was found. These findings are in a good agreement with the higher numbers of myofilaments per myofibril in the right ventricle, reported in literature.

Myosin isozymes in normal and cross-reinnervated cat skeletal muscle fibers.

Immunocytochemical characteristics of myosin have been demonstrated directly in normal and cross-reinnervated skeletal muscle fibers whose physiological properties have been defined. Fibers belonging to individual motor units were identified by the glycogen-depletion method, which permits correlation of cytochemical and physiological data on the same fibers. The normal flexor digitorum longus (FDL) of the cat is composed primarily of fast-twitch motor units having muscle fibers with high myosin ATPase activity. These fibers reacted with antibodies specific for the two light chains characteristic of fast myosin, but not with antibodies against slow myosin. Two categories of fast fibers, corresponding to two physiological motor unit types (FF and FR), differed in their immunochemical response, from which it can be concluded that their myosins are distinctive. The soleus (SOL) consists almost entirely of slow-twitch motor units having muscle fibers with low myosin ATPase activity. These fibers reacted with antibodies against slow myosin, but not with antibodies specific for fast myosin. When the FDL muscle was cross-reinnervated by the SOL nerve, twitch contraction times were slowed about twofold, and motor units resembled SOL units in a number of physiological properties. The corresponding muscle fibers had low ATPase activity, and they reacted with antibodies against slow myosin only. The myosin of individual cross-reinnervated FDL muscle units was therefore transformed, apparently completely, to a slow type. In contrast, cross-reinnervation of the SOL muscle by FDL motoneurons did not effect a complete converse transformation. Although cross-reinnervated SOL motor units had faster than normal twitch contraction times (about twofold), other physiological properties characteristic of type S motor units were unchanged. Despite the change in contraction times, cross-reinnervated SOL muscle fibers exhibited no change in ATPase activity. They also continued to react with antibodies against slow myosin, but in contrast to the normal SOL, they now showed a positive response to an antibody specific for one of the light chains of fast myosin. The myosins of both fast and slow muscles were thus converted by cross-reinnervation, but in the SOL, the newly synthesized myosin was not equivalent to that normally present in either the FDL or SOL. This suggests that, in the SOL, alteration of the nerve supply and the associated dynamic activity pattern are not sufficient to completely respecify the type of myosin expressed.

The contractile properties, histochemistry, ultrastructure and electrophysiology of the cricothyroid and posterior cricoarytenoid muscles in the rat.

The contractile, histochemical, morphological and electrophysiological properties of two rat laryngeal muscles, the cricothyroid and posterior cricoarytenoid, have been measured. Both muscles act during respiration to maintain upper airway patency and an even distribution of air in the lungs. The cricothyroid and posterior cricoarytenoid are fast-twitch muscles, having contraction times of 3.4 and 7.2 ms respectively, high myosin ATPase activity, abundant sarcoplasmic reticulum (with average volumes of 9% and 15%, respectively, of the fibre volume) and T-system membrane (with average areas of 0.4 and 0.5 micron 2 micron -3 of fibre). The large areas of T-tubule membrane are reflected in the average specific membrane capacities of 6.5 muF cm-2 to 10.5 muF cm-2, which are high considering the small diameter of the fibres (20-30 micron). Of the two muscles, the posterior cricoarytenoid has the faster contraction time and the more abundant sarcoplasmic reticulum content. In addition, the posterior cricoarytenoid is less resistant to fatigue and demonstrates lower succinic dehydrogenase activity. The fatigability of this muscle, coupled with its general lack of functional reserve, suggest that its failure may contribute to upper airway obstruction during respiratory distress.

Skeletal muscle fibre composition in the dog and its relationship to athletic ability

Skeletal limb muscles of the dog could generally be differentiated into three fibre types according to myosin adenosine triphosphatase (ATPase) (pH 9.4) and succinic dehydrogenase activities. However, because this was not always possible, for comparative purposes only, division into low myosin ATPase (slow twitch) type I and high myosin ATPase (fast twitch) type II fibres was used. The percentage of these fibre types in m deltoideus, m triceps brachii caput longum, m vastus lateralis, m gluteus medius, m biceps femoris and m semitendinosus was examined in the greyhound, crossbred and foxhound. In all muscles the greyhound had a significantly higher percentage of fibres with high myosin ATPase activity at pH 9.4 than the other breeds, with almost 100 per cent in most muscles examined. The activities of nine enzymes and glycogen concentration were determined in m gluteus medius and m semitendinosus of the greyhound and crossbred. Significantly higher levels of creatine kinase, aldolase, alanine aminotransferase and citrate synthase and significantly lower activities of 3-hydroxyacyl coenzyme A dehydrogenase and hexokinase were found in both muscles of the greyhound. The implications of these findings are discussed.

Muscle fibre type composition of a number of limb muscles in different types of horse

Skeletal muscle of the equine was differentiated into three fibre types according to myosin ATPase (pH 9.4) and succinic dehydrogenase activity. The percentage of these types was determined in the musculus deltoideus, m triceps brachii caput longum, m gluteus medius, m semitendinosis, m biceps femoris and m vastus lateralis of the thoroughbred, Shetland pony, pony, heavy hunter and donkey. In addition the m gluteus medius was examined in the arab and American racing quarterhorse. High myosin ATPase activity fibres varied from a mean of 93.2 per cent in the m gluteus medius of the quarterhorse to 58.2 per cent in the m vastus lateralis of the donkey. In the m gluteus medius it was found that the percentage of high mycosin ATPase (pH 9.4) fibres varied significantly among breeds and these differences were related to the sprinting speed of the breed.

Histochemical dichotomy of extrafusal and intrafusal fibers in an avian slow muscle.

AbstractThe avian anterior latissimus dorsi (ALD) is unique amongst vertebrates since it has been considered to be a true slow (or tonic) skeletal muscle. While the structure and function of the extrafusal fibers in the ALD have been intensively investigated, the intrafusal fibers of its muscle spindles and their relationship to the surrounding extrafusal fibers in this muscle have been virtually neglected. Serial frozen sections of this muscle from normal adult domestic chickens were tested for two separate enzymes: myosin ATPase after preincubations at differing pH (Brooke and Kaiser, '69) and NADH‐tetrazolium reductase, a mitochondrial‐bound oxidative enzyme. Both enzyme reactions were able to detect two distinct categories of extrafusal fibers in this muscle, as well as two classes of intrafusal fibers in its muscle spindles.Neither of the extrafusal fiber‐types reacted like typical fast (or twitch) fibers for myosin ATPase; they did not show a characteristic reversal in their relative staining patterns throughout the alkaline (pH 9.4) to acid (pH 4.6 and 4.3) preincubation range. The majority of fibers (type 1) were significantly larger in their cross‐sectional size, consistently stained lightly for ATPase, and showed high NADH‐TR activity. They represented about 84% of the total fiber population (n = 3540 ± 75). The other set of extrafusal fibers (type 2) constituted the remaining 16% of the total fiber population. They were smaller in diameter, exhibited high myosin ATPase activity, and reacted less intensely for the oxidative enzyme.The histochemical characteristics of the two kinds of intrafusal fibers were profoundly different from those observed in the extrafusal fibers. Their crosssectional fiber diameters were not significantly different from each other, and they exhibited a reversal in their staining reactions for myosin ATPase following acid preincubation for this enzyme.The results of this study concur with recently published reports of extrafusal fiber heterogeneity in the slow ALD muscle of the chicken. In addition, this work clearly demonstrates a histochemical dichotomy amongst the intrafusal fibers of muscle spindles in this muscle.

The effect of training and detraining on muscle composition in the horse.

1. Percutaneous needle biopsies were obtained from six limb muscles in six horses before and during a training programme of 10 or 15 weeks designed to involve both aerobic and anaerobic work. In a subsequent detraining period, biopsies were also taken after 5 and 10 weeks. 2. Samples were analysed biochemically for enzyme activity of lactic dehydrogenase (LDH), creatine phosphokinase (CPK), aldolase (ALD), citrate synthase (CS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) and for glycogen content. Fibre typing was carried out histochemically before and 10 weeks after commencement of training. 3. There was a significant increase in the percentage of high myosin ATPase activity pH 9-4/high oxidative (FTH) fibres with a corresponding decrease in high myosin ATPase activity pH 9-4/low oxidative (FT) fibres and low myosin ATPase activity pH 9-4/high oxidative (ST) fibres after 10 weeks training. 4. During training, enzyme activities increased progressively but at different rates with an approximate twofold increase in all of the enzymes except CPK by the end of the training period. Changes in all the muscles studied were similar. Glycogen content increased by approximately 33% which was significant when all the muscles were considered together. 5. A decrease in enzyme activity occurred after 5 weeks detraining. However at 10 weeks a consistent but inexplicable increase in all enzyme levels, except CS again occurred. 6. It is concluded that training increased greatly the activity of enzymes involved in both aerobic and anaerobic metabolism.

Differentiation of myosin in soleus and extensor digitorum longus muscle in differnt animal species during development.

CA2+-ATPase activity and light chains of myosin prepared from fast and slow muscles of rat guinea-pig and rabbit were studied during development from embryonic to old age to establish further correlation with the well-known developmental changes in contraction properties of these muscles. The changes involve the slow soleus muscle much more than the fast extensor digitorum longus muscle. Myosin-ATPase activity of the soleus muscle before or at birth is higher than in the muscle of adult animals. Myosin from the soleus muscle of embryos or newborn animals reveals light chains of myosin of both fast and slow type (with a preponderance of light chains of fast type in 26-days-old rabbit embryos). During postnatal development the amount of light chains of the fast type decreases, that of the slow type increases. Myosin from the soleus muscle of adult animals contains only light chains of the slow type. However, myosin from the soleus muscle of 30-months-old rats exhibits high myosin ATPase activity and contains light chains of myosin of both slow and fast type as in perinatal development. This is in agreement with the shortening of contraction time observed in this muscle in very old age. Thus developmental differentiation of myosine in the soleus muscle is followed by a trend of levelling out of the differences between fast and slow muscles of senescent animals. No such "biphasic" development is observed with respect to the fast extensor digitorum longus muscle.

A histochemical study of postnatal differentiation of skeletal muscle with reference to functional overload

Postnatal differentiation and growth of the fibers comprising the tonic soleus and phasic plantaris muscles, were investigated histochemically in kittens. Compensatory hypertrophy was induced by ablation of the synergistic gastrocnemius muscle. At birth both muscles consist of relatively homogeneous fiber populations as demonstrated by myosin ATPase and succinic dehydrogenase activities and glycogen content (PAS method). Differential myosin ATPase activities become evident during the first week (soleus and plantaris), while diversification of fiber types according to SDH and glycogen develop gradually and independently during the first 2 mo of life (plantaris). Compensatory hypertrophy is associated with a substantial enlargement of both dark and light fibers (incubated for myosin ATPase) and, with increases in SDH activity which are most notable in fibers that normally are low in this enzyme. The normal growth associated reduction in the percentage of fibers with high myosin ATPase activity is significantly accelerated in the hypertrophic soleus, while the hypertrophic plantaris, which normally undergoes only a slight reduction in the percentage of such fibers, is unaffected. These results underline the paramount role of the nerve fiber in the process of differentiation but also indicate that functional overload exerts a modifying influence on this process.

Histochemical composition, contraction speed and fatiguability of rat soleus motor units

The relation between the histochemical myosin ATPase and SDH activities and the speed and endurance of contraction at 34.5–35.5°C was studied in 28 rat soleus motor units. 1. (1) Myosin ATPase activity was associated with speed and from the intensity of the reaction it was possible to predict the contraction time of a fast unit with unexpected accuracy. Units with a strong myosin ATPase reaction after formaldehyde fixation and an inhibited reaction after acid preincubation at pH 4.35 had a contraction time of 15–20 msec. Units with moderate staining reactions had a contraction time of 21–23 msec and those with an inhibited reaction after fixation and strong reaction after preincubation had contraction times of 26–44 msec. The fibres of fast and slow units appeared histochemically uniform; fibres of intermediate units revealed subtle variations in the intensity of the ATPase staining. Three units were histochemically transitional between two adjacent groups. 2. (2) The direct correlation between SDH activity and endurance was confirmed. Resistance to fatigue was in addition inversely related to speed. Despite the higher SDH activity in fast and intermediate motor units compared with slow units, the decline in tetanus tension in the three groups was proportionate to their speed of contraction. The greater stability of slow units in a fused tetanus was the result of better matching between the capacity of neuromuscular transmission and tetanic fusion frequency and in a moderate, incomplete tetanus was associated with a larger increase in plateau tetanus-twitch ratio. 3. (3) The intense SDH activity in many fibres with high myosin ATPase activity typical for limb muscles of small animals with great rapidity of limb movements serves to compensate for the higher energy expenditure demanded by their operation at high speed; they therefore combine endurance with speed, particularly apparent in strong repetitive phasic contractions. The independent variability of myosin ATPase and mitochondrial enzymes enables a wide range of specifications of motor units with regard to speed and endurance, required by muscles with different functions.

Comparative purification of myocardial myosin and antigenic specificity of the two light chains.

Abstract Dog myocardial myosin preparations, purified according to the procedures presented here, utilizing either one or two (NH4)2SO4 fractionations, contained no major contaminants which could be detected by disc gel electrophoresis, and exhibited high myosin ATPase activity. The low molecular weight components (light chains) were dissociated from the rest of the molecule by denaturing with urea; the chains were further purified by column chromatography. Procedures were a modification of those used for purification of skeletal muscle myosin light chains. According to immunoanalyses the two myocardial myosin light chains showed antigenic specificity.