Different Types Of Muscle Research Articles

Glutamine transport in human skeletal muscle.

Sarcolemmal vesicles isolated from human skeletal muscle obtained at surgery showed approximately 14-fold enrichment of sarcolemmal marker enzymes 5'-nucleotidase and K-stimulated phosphatase. [3H]glutamine transport in these vesicles was stereospecific, largely Na dependent, and tolerated Li-for-Na substitution. Glutamine transport was stimulated by an inside negative membrane potential, and 25 mM glutamine stimulated 22Na (0.1 mM) uptake into vesicles by 50%, indicating rheogenic cotransport of Na and glutamine. Alanine transport was Na dependent but did not tolerate Li-for-Na substitution. Transport of L-[3H]glutamine was inhibited by 35-65% with a 20-fold excess of glutamine, asparagine, and alanine; cysteine, alpha-(methylamino)isobutyrate, and 2-amino-2-norborane carboxylic acid had smaller inhibitory effects, although cysteine had an unusually large inhibitory effect on glutamine transport at 1,000-fold excess compared with most other amino acids. Glutamine transport showed sensitivity to pH values < 7.0. Glutamine transport consisted of a Na-dependent and a Na-independent component, both of which appeared saturable. The kinetic characteristics of the Na-dependent component were different in different types of muscles, with half-maximal concentrations (mM) varying from 1.6 +/- 0.4 (tibialis anterior) to 0.56 +/- 0.0.2 (gluteus maximus) and maximal velocity (pmol.mg protein-1.s-1) of 1.3 +/- 0.27 to 5 +/- 1.25 in the same muscles. The results demonstrate both marked similarities and important differences between the principal glutamine transporter in human skeletal muscle and the known system Nm transporter in rat skeletal muscle.

In-vivo regulation of messenger RNA encoding insulin-like growth factor-I (IGF-I) and its receptor by diabetes, insulin and IGF-I in rat muscle

The effects of continuous or acute administration of insulin or insulin-like growth factor-I (IGF-I) on IGF-I mRNA and IGF-I receptor mRNA were studied in the skeletal muscle (gastrocnemius), heart muscle and vascular smooth muscle (aorta) of non-diabetic and diabetic rats using a solution hybridization assay. The levels of IGF-I mRNA in the different types of muscle markedly decreased by diabetes, whereas changes in IGF-I receptor mRNA were less consistent. Continuous infusion of diabetic rats with insulin (28 or 35 nmol/day) for 4 days normalized the altered levels of IGF-I mRNA and IGF-1 receptor mRNA. Infusion of equimolar concentrations of IGF-I did not affect IGF-I mRNA, but decreased the level of IGF-I receptor mRNA in skeletal muscle. In acute experiments, rats were injected with equipotent blood glucose-lowering doses of insulin (14 nmol) or IGF-I (107 nmol). Insulin did not significantly affect levels of IGF-I mRNA, but decreased levels of IGF-I receptor mRNA in skeletal muscle and aorta. IGF-I increased levels of IGF-I mRNA in heart muscle, and markedly decreased levels of IGF-I receptor mRNA in skeletal muscle and heart muscle from non-diabetic and diabetic rats. In conclusion, exogenous IGF-I and insulin can increase IGF-I mRNA and decrease IGF-I receptor mRNA, indicating that both insulin and IGF-I can act as regulators of the IGF-I system in muscle in vivo.

Functional responses of different muscle types of the female rat urethra in vitro

The influence of muscle type on functional responses of the female rat urethra was investigated using morphological and functional in-vitro techniques. The urethral submucosa was found to contain longitudinally or obliquely oriented smooth muscle cells. The muscularis layer is composed of circularly oriented muscle cells. Near the bladder orifice smooth muscle fibres dominate, but in the mid-urethra the vast majority is circularly oriented striated muscle cells. Circular preparations responded to electrical field stimulation in vitro with a rapid contraction. Stimulation with single impulses resulted in a twitch response; frequencies exceeding 5-10 Hz induced a summation and tetanus. The response was unaffected by phenoxybenzamine, propranolol and scopolamine and had a low sensitivity to calcium-free solution but was sensitive to suxamethonium and tetrodotoxin. Using longer impulse trains stimulation evoked also a slow contraction, sensitive to calcium-free solution. In longitudinal preparations stimulation induced a relaxation followed by a contraction, responses much smaller than those seen in the circular preparations. Both preparations relaxed on addition of calcitonin gene-related peptide or capsaicin. The relaxation to calcitonin gene-related peptide was larger than that to capsaicin in longitudinal preparations but equally large in the circular ones. Substance P and 5-hydroxytryptamine contracted both preparations. The longitudinal urethra showed a larger contraction to 5-hydroxytryptamine than to substance P, whereas both substances induced similar responses in the circular preparations. The study shows a similar muscle arrangement in the female rat urethra as described in humans and further points to a functional differentiation between the different types of muscle.

Expression of two myogenic regulatory factors myogenin and MyoDl during mouse embryogenesis

MyoD1 and myogenin are muscle-specific proteins which can convert non-myogenic cells in culture to differentiated muscle fibres, implicating them in myogenic determination. The pattern of expression of MyoD1 and myogenin during the early stages of muscle formation in the mouse embryo in vivo and in limb-bud explants cultured in vitro, indicates that they may have different functions in different types of muscle during development.

Physiology of Esophageal Motor Function

The esophagus is a region with three functional zones: (1) the upper esophageal sphincter; (2) the esophageal body; and (3) the lower esophageal sphincter. Control mechanisms within the central nervous system and peripherally serve to integrate these functional zones in a region where voluntary and involuntary control mechanisms and the activity of two different types of muscle are intimately coordinated. The distal 50 to 60 per cent of the esophagus in humans is entirely smooth muscle. Extrinsic control for esophageal motor function resides in a brainstem swallowing center with an afferent reception system, an efferent system of motor neurones, and a complex organizing or internuncial system of neurones. Sensory information from the esophagus is carried in the vagus nerves, but sensory pathways are also present in sympathetics entering the spinal cord. The vagus nerve receiving fibers both from the nucleus ambiguus and the dorsal motor nucleus innervates the striated and smooth muscle esophagus, respectively, including the sphincters. There is a myenteric nerve plexus in both the striated and smooth muscle segments. In the smooth muscle esophagus, there are two important effector neurones, an excitatory cholinergic neurone, and a nonadrenergic, noncholinergic (NANC) inhibitory neurone. The striated muscle contraction is directed and coordinated by sequential excitation through vagal fibers programmed by the central control mechanism. There are at least four potential control mechanisms for peristalsis in the smooth muscle esophagus: efferent motor fibers programmed by the swallowing center fire sequentially during peristalsis; the intramural neural mechanism can be excited to produce peristalsis near the onset of stimulation or with a delay after termination of stimulation; there is evidence for myogenic propagation of a peristaltic contraction. In humans, swallow-induced peristalsis is cholinergic and appears to result primarily from sequencing and activation of the intramural excitatory cholinergic neurones. Both central and peripheral levels of control are highly integrated to focus on the excitatory cholinergic neurones. It is likely that under normal circumstances, the central control mechanism exerts the dominant influence on these neurones for initiation and coordination of peristalsis in the smooth muscle esophagus. In humans, resting tone in the lower esophageal sphincter is predominantly cholinergic, but this tone is regulated by a balance between many excitatory and inhibitory influences. The relaxation on swallowing is caused by active inhibition of the muscle through NANC inhibitory neurones and cessation of tonic neural excitation to the

Some properties of different skeletal muscle fiber types: comparison of reference bases.

Several biochemical components of the white portion of the gastrocnemius (WGM), plantaris (PM), and soleus (SM) muscles of the rat and middle gluteal (MGM) muscle of the horse were compared based on wet and dry weight, protein, and total creatine concentrations ([TCr]). The water content was similar for the rat hindlimb muscles, however, the concentrations of protein, ATP, phosphocreatine (PCr), creatine, and glycogen ranked as SM less than PM less than WGM for all reference bases except total creatine. In contrast, concentrations of ATP, creatine, and PCr were similar in all muscles studied when expressed as ratios of [TCr]. Horse MGM had the lowest percent of water and protein per gram wet or dry weight but highest glycogen concentration of the muscles studied, irrespective of the reference base used to express concentrations. Coefficients of variation were lowest when muscle constituents were related to [TCr]. It is concluded that expressing muscle constituents relative to total creatine results in the smallest variation and is a good method for making comparisons between muscles of similar fiber composition. However, essential information concerning different types of muscle may be lost when this reference base is used.

Energetics studies of muscles of different types.

31P-NMR studies were performed in isolated perfused striated and smooth muscles. Important qualitative and quantitative differences were found in resting muscles. In resting fast-twitch skeletal muscle the chemical potential of ATP obtained from the measured intracellular pH, ATP and inorganic phosphate concentrations and from the ADP concentrations calculated from the position of the creatine kinase equilibrium was -72 kJ/mol ATP. This high value was the result of a very low free ADP and inorganic phosphate content. In resting slow-twitch skeletal muscle, in smooth muscle, and in cardiac muscle at low work rates (literature data), the chemical potential of ATP was lower (approximately -50 to -60 kJ/mol), the difference being primarily due to a much higher inorganic phosphate content (especially in slow-twitch and smooth muscle) and/or a higher ADP concentration (especially in cardiac muscle). Upon stimulation or, for the heart, working at higher work rates, the pattern of chemical changes of phosphocreatine, creatine and inorganic phosphate was the same for all types of muscle. The phosphocreatine levels decreased and the inorganic phosphate concentration increased stoichiometrically without a change in the ATP content so long as the phosphocreatine pool was not totally depleted (greater than or equal to 10%). The rate and extent of these chemical changes was dependent on the inherent ATPase and ATP synthesis rates. The exception was in the intracellular pH changes. In fast-twitch and smooth muscle, pH decreased with contractile activity, as expected from the large glycolytic capacity. However, an alkalinization was observed in slow-twitch skeletal muscle and this difference was attributed to the uptake of H+ during the net hydrolysis of phosphocreatine to creatine plus inorganic phosphate, and to the absence of significant lactate production. The pH of cardiac muscle does not appear to change with work load. The common bioenergetic pattern in all types of muscles is consistent with a graded increase in ADP concentration (from below to well above the apparent Km for nucleotide translocase ANT) with increasing work as a regulator of mitochondrial respiration. In fast-twitch muscle these changes are also accompanied by large changes in inorganic phosphate concentration (3-30 mM) which may also play a role in metabolic regulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Specificity of activated glucorticoid receptor expression in heart and skeletal muscle types

Muscle metabolic responses to glucocorticoids are specific to fiber type. The present study revealed that a definite pattern exists in the formation of the two thermally activated glucocorticoid receptor complexes among the different types of muscle. Fiber types that enlarge from glucocorticoids (heart) contained the highest relative distribution of binder II and lowest content of binder IB. Fibers that atrophy from glucocorticoids (white muscle) contained negligible content of binder II and the highest appearance of binder IB. The formation of binder IB could not be explained by differences in proteolysis among the cell types. These results are consistent with the hypothesis that specific receptor forms may regulate the glucocorticoid induction of muscle hypertrophy and atrophy.

3 - Adverse Effects of Drugs in Later Pregnancy

Although hepatitis E virus (HEV) transmission has been demonstrated after consumption of products containing infected pig liver, human cases can be also associated with other pig meat products, such as sausages. Data on HEV viremia and dissemination in muscle meat of infected animals are still sparse, especially during long-term infection. Previously, we have shown that experimental co-infection of pigs with HEV and porcine reproductive and respiratory syndrome virus (PRRSV) lengthens HEV infection up to 49 days and increases the likelihood of the presence of HEV RNA in the liver of the pig at a later stage of infection. In the present study, we show that during experimental HEV-PRRSV co-infection, prolonged HEV viremia, up to 49 days post-inoculation (dpi), is detected. The long-term viremia observed was statistically associated with the absence of HEV seroconversion. HEV RNA was also frequently detected, at a late stage of infection (49 dpi), in the three different types of muscle tested: femoral biceps, psoas major or diaphragm pillar. The HEV RNA load could reach up to 1 · 106 genome copies per gram of muscle. Detection of HEV in muscle meat was statistically associated with high HEV loads in corresponding liver and fecal samples. The presence of HEV in pig blood, femoral biceps and major psoas, corresponding to ham and tenderloin muscles respectively, is of concern for the food industry. Hence, these results indicate new potential risks for consumers and public health regarding pork products.

SARCOPLASMIC RETICULUM IN THE ADDUCTOR MUSCLES OF A BERMUDA SCALLOP: COMPARISON OF SMOOTHVERSUSCROSS-STRIATED PORTIONS

The adductor muscle of the Bermuda scallop, Pecten ziczac, is composed of two different types of muscle: cross-striated and smooth. The major portion consists of ribbon-shaped cross-striated muscle cells averaging about ten µm by 1.5 µm in cross section. Each cell contains only one myofibril. In some of the wider cells, an extra sarcomere sometimes is inserted in the lateral part of the myofibril creating a vernier. The individual striated muscle cells do not span the entire length of the adductor but are connected at their ends via junctions similar to intercalated discs. The minor portion of the adductor muscle consists of smooth muscle cells which are fusiform averaging 6 µm in diameter. There are no specialized cell surface invaginations in either muscle type that correspond to a T-tubule or caveolae system. The sarcoplasmic reticulum in both muscles is confined to the area just beneath the cell surface. In both muscle types, the sarcoplasmic reticulum systems have distended vesicles connected to the cell membrane via surface couplings. These vesicles are interconnected by one to seven tubular elements of the sarcoplasmic reticulum to form a closed and continuous system. The tubular elements of the sarcoplasmic reticulum in the cross-striated muscle are fairly uniform in bore, 40 nm in diameter, as compared to the irregular bore in smooth muscle, 15-40 nm. The striated muscle has twice as much of its surface covered with sarcoplasmic reticulum as does the smooth muscle. Moreover, the striated muscle cells have about 4% of their cross-sectional area devoted to sarcoplasmic reticulum while the smooth muscle cells have only 0.5%. This eight-fold difference in the amount of sarcoplasmic reticulum in the striated muscle is consistent with its reported 50-fold faster contraction rate and 128-fold faster relaxation time over that of the scallop adductor smooth muscle.

Patterns in mammalian muscle energetics.

A description of cellular energetics of muscular contraction is given in terms of the rates and extents of high-energy phosphate splitting during contractile activity, in terms of high-energy phosphate resynthesis by respiration and net anaerobic glycolysis, and in terms of the associated uptake and/or release of H+. These chemical changes have been studied quantitatively by rapid freeze-clamping methods and by 31P-NMR methods. The pattern of chemical changes in a fast-twitch glycolytic muscle is rapid depletion of phosphocreatine and later ATP levels, cellular acidification, and a much slower rate of resynthesis of high-energy phosphate compounds during the recovery period afterwards than occurs in the slow-twitch oxidative muscles. In steady-state contractile activity below the maximal, graded levels of high-energy phosphates and of cellular respiration are achieved in both fast-twitch and slow-twitch muscles. Within the metabolic range up to the maximal aerobic capacity, which differs several-fold for different fibre types, this gradation is mediated by the creatine kinase reaction and phosphocreatine stores. Thus while the amount of enzyme present and the content of phosphocreatine differs among muscles of different types, the same general energetic function is seen to occur in all muscle cells. The creatine kinase reaction is both an energy reservoir and a buffer preventing large swings in the ATP/ADP ratios.

The effect of fasting and hypocaloric diets on the functional and metabolic characteristics of rat gastrocnemius muscle.

Previous observations have shown that in human subjects with malnutrition and after prolonged fasting, there are characteristic changes in the force-frequency response, relaxation rate and power of muscle during a 30 s stimulus (fatigue). In order to characterize these findings under carefully controlled conditions, in different types of muscle and to correlate them with changes in muscle structure, composition and biochemical status, we developed an animal model in rats. In this model, nutrient restriction, both after an acute fast and after chronic hypocaloric feeding, resulted in: (a) loss of force during high frequency stimulation but preservation of contraction-relaxation characteristics during low frequency stimulation; (b) slower muscle relaxation rate at high frequency stimulation; (c) increased muscle fatiguability at high frequency stimulation. Measurements of muscle enzymes showed that acute fasting resulted in a reduced content of glycolytic enzymes, but preservation of oxidative enzymes, while chronic hypocaloric dieting resulted in a reduction in both classes of enzyme. There was no significant change in ATP, AMP or energy charge, or in intracellular sodium, potassium and magnesium levels. Creatine phosphate was normal in acutely fasted animals but low in those fed hypocalorically. By contrast, increased intracellular calcium and ADP levels were seen in both fasted and hypocalorically fed animals. These findings suggest that subtle disturbances of intracellular energy states with altered calcium flux may be of importance in the genesis of muscle dysfunction caused by malnutrition.

Ca 2+ and the contractile proteins

Troponin regulation can be divided into two categories, primary and secondary. While the former underlies the processes common to troponin-regulated muscles, the latter varies between different types of muscle. One example of secondary regulation is the Ca2+ dependent interaction of troponin T and troponin C, which tends to suppress the myosin-actin-ATP interaction at relatively high Ca2+ concentrations, say, 10(-4)M. This interaction is marked in fast skeletal muscle, but weak in cardiac muscle. Since the Ca2+ concentration in fast skeletal muscle can physiologically reach a high level, this interaction may be considered as a kind of self-defense mechanism to avoid excess contraction. Cardiac muscle, which carries out its contractile cycle at lower Ca2+ concentrations, does not require such a mechanism, but under pathological conditions where the Ca2+ concentration could reach a high level, the lack of this mechanism might be detrimental to the contractile system.

Polyamine metabolism in muscles of mice and rats.

Polyamine biosynthesis in different types of muscle was studied in mice and rats. A sex difference of polyamine biosynthesis in the gastrocnemius of the mouse was demonstrated. Ornithine decarboxylase activity was found to be several-fold higher in the gastrocnemius of the male mouse than in that of the female. Orchiectomy resulted in a decline of enzyme activity in the gastrocnemius. This effect was reversed by the administration of testosterone. The elevation of ornithine decarboxylase activity in the gastrocnemius by testosterone was reflected in an increased content of the polyamines in the muscle. Muscles of other types, i.e. soleus, heart and urinary bladder were shown to be virtually unresponsive to testosterone treatment. Neither were the muscles of the rat, including gastrocnemius, found to be affected by the androgen.

Response of ventilatory muscles of the rat to endurance training.

The effect of endurance training on the oxidative and glycolytic potentials of the diaphragm and intercostal muscles of rats has been studied. Training consisted of treadmill running (28 m/min, 60 min/day, 5 days/wk) for periods ranging from 8-26 weeks. Exercise of similar duration and intensity produced a glycogen depletion in the diaphragm and intercostal muscles of nontrained rats. Oxidative potential was estimated from the activity of the mitochondrial marker enzyme succinate dehydrogenase (SDH). The activities of phosphorylase (PHOS), hexokinase (HK), and lactate dehydrogenase (LDH) were determined as well as the distribution of the LDH isozymes. SDH activity averaged 44 (42-51) and 17 (10-22)% (P less than 0.0l) greater in the plantaris and diaphragm muscles, respectively, after 8-12 weeks of endurance running as compared to the sedentary animals. There was no change in the SDH activity of the intercostal muscles or in the activities of the glycolytic enzymes. There was also no change in the distribution of the isozymes of LDH. Extending the duration of the training program to 26 weeks did not produce any additional alteration in the magnitude of the adaptation observed after the initial training period. Comparative studies of different types of muscles demonstrated that the diaphragm, although having a fiber composition somewhat similar to that of a fast-twitch skeletal muscle, has a metabolic profile that is intermediate between pure slow twitch skeletal muscle and cardiac muscle.

Mitochondrial proteins of fast-twitch glycolytic, fast-twitch glycolytic-oxidative and slow-twitch-oxidative rabbit skeletal muscle

1. 1. Proteins of mitochondria isolated from rabbit slow-twitch oxidative muscle (m. soleus), fast-twitch-glycolytic muscle (m. psoas) and fast-twitch-glycolytic-oxidative muscle (m. gastrocnemius) were subjected to isoelectrofocusing and subsequent sodium dodecyl sulphate gel electrophoresis. 2. 2. About 120 protein components have been shown to exist in the mitochondria investigated, their molecular weights ranging from 10,000 to 200,000 and isoelectric points from 5.5 to 8.7. 3. 3. Although the general protein pattern of the mitochondria from different muscle types investigated was similar, some differences in the protein composition of mitochondria isolated from functionally different types of muscle have been found.

Evolution of homologous physiological mechanisms based on protein sequence data

1. 1. Genetic duplications can give rise to homologous physiological mechanisms that include structurally related protein components. There are many such examples of related proteins within the human body. 2. 2. Evolutionary histories showing the origins and subsequent divergences of these distantly related proteins can be derived from the protein sequences and correlated with the functional characteristics of these proteins. 3. 3. The hormones related to glucagon provide an example of homology of physiological mechanisms and emergence of new functions subsequent to gene duplications. 4. 4. The proteins related to troponin C illustrate the participation of distantly related proteins in the same mechanism (muscle contraction), the relationship of proteins characteristic of a specialized tissue to proteins found in all eukaryote cells, and the correlation of genetic duplications with the evolutionary appearance of different types of muscle.

Lactate oxidative capacity in different types of muscle

The capacity of different types of muscle homogenates to oxidize lactate (2.0 to 10.0 mM) under state 3 conditions was determined in the context of their maximal pyruvate oxidative capacity. Both cardiac and fast-oxidative-glycogenolytic (FOG) muscle oxidized 10 mM lactate at approximately 100% of their respective capacities to maximally oxidize pyruvate (2.5 mM); whereas slow-oxidative (SO) and fast-glycogenolytic (FG) skeletal muscle oxidized lactate at 78% and 63% of their respective capacities for pyruvate. The lactate oxidation correlated with (a) pyruvate and NADH oxidation and (b) the gross lactate dehydrogenase heart type isozyme profile in the different muscle types. These results suggest that different muscle types possess quantitatively and qualitatively different capacities for metabolizing lactate.

Exercise-induced changes of reactivity of different types of muscle on glycogenolytic effect of adrenaline.

In the investigations presented it was found that the glycogenolytic effect of adrenaline in the skeletal muscle of resting rats depends on the type of muscle: the hormone exerts the least effect in the white muscle and the greatest effect in the intermediate one. There was a cumulative effect of adrenaline in a dose of 0.1 mg/kg and exercise on the glycogen level in the white muscle. In the red and intermediate muscles the exercise-induced glycogen depletion rate was very rapid and no additional effect of adrenaline on glycogen level was observed. No repletion of glycogen in the white muscle occurred during the first 3 h of the post-exercise recovery, and adrenaline further decreased the glycogen level in this muscle. In the red and intermediate muscles full repletion of glycogen took place already during the first hour of recovery. A dose of 0.1 mg/kg adrenaline had no effect on the glycogen repletion rate in the red muscle and only partly inhibited it in the intermediate muscle. A dose of 0.5 mg/kg adrenaline prevented the glycogen repletion in both types of muscles. During the exercise as well as during the post-exercise recovery the hyperglycemic effect of adrenaline was decreased.

Electrophoretic investigation of muscle extracts of low ionic strength

The composition of protein subunits extracted from muscle homogenates of various types by salt media of low ionic strength was studied by electrophoresis in polyacrylamide gel with sodium dodecyl sulfate. Extracts from smooth muscles contained a premyosin subunit with a molecular weight of 230,000, the heavy chain of myosin, actin, and certain other proteins. Extracts of low ionic strength from smooth muscles possessed Mg- and Ca-activated ATPase activity. A premyosin subunit also was found in extracts of low ionic strengths from homogenates of skeletal muscles. It is postulated that the premyosin subunit is a component of the enzyme system responsible for the ATPase properties of extracts of low ionic strengths from homogenates of different types of muscle.