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Biomedical subjects

P M Nemeth

Publications and source records attributed to P M Nemeth.

At least 37 records · Page 2Linked to original sources
PubMed1988

Association between biochemical and physiological properties in single motor units.

Motor units from the cat tibialis posterior muscle were examined for an association between physiological and biochemical properties. Functionally isolated motor units were categorized on the basis of their physiological properties. This was followed by quantitative microbiochemical analysis of single muscle fibers from each unit, identified in cross sections using the glycogen-depletion method. The activities of malate dehydrogenase and beta-hydroxyacyl-CoA dehydrogenase distinguished between fatigable (type FF) and fatigue-resistant (types FR and S) units. The activities of both lactate dehydrogenase and adenylokinase were higher in fast- than in slow-contracting units. Cluster analyses, based on both physiological and biochemical properties or on biochemical properties alone, produced groupings identical to types FF, FR, and S. The association between physiological and biochemical properties substantiates the idea that biochemically distinct groups of motor units correspond to physiologically identifiable groups.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1988

Activation of muscle fibers in individual motor units revealed by 2-deoxyglucose-6-phosphate.

Motor units of the cat tibialis posterior muscle were selectively activated by prolonged electrical stimulation of functionally isolated motor axons in situ. During the activation, the glucose analog 2-deoxyglucose (DG) was administered systemically. Single muscle fibers were subsequently examined for accumulation of the metabolite 2-deoxyglucose-6-phosphate (DG6P) by an analytical assay and for depletion of glycogen by a PAS glycogen-specific staining reaction (periodic acid Schiff; PAS). In general, levels of DG6P were 20 times greater in unstained (PAS-negative) fibers compared with stained (PAS-positive) fibers. However, some glycogen-depleted fibers, particularly in putative ischemic fascicles of the muscle, did not have elevated DG6P, suggesting that depletion of glycogen is not always a reliable indicator of fiber activation. Furthermore, the PAS-staining reaction was not necessarily indicative of quantitative glycogen levels in single fibers. Thus, this report shows that DG6P accumulation enhances the identification of motor-unit fibers selectively activated via their common motor-nerve axon. Evidence is also presented for differential glucose uptake in muscle fibers of different phenotype, thereby indicating that the DG6P measurement in muscle has broad applicability to the investigation of cellular glucose utilization.

Animals↗
PubMed1988

A novel method for measurement of triglyceride lipase activity: suitable for microgram and nanogram quantities of tissue.

The measurement of triglyceride lipase activity in microgram and nanogram quantities of tissue is reported. The method involves quantitation of glycerol released from a triglyceride substrate, which is shown to provide a value of approximately one-third of that obtained by quantitation of free fatty acid release. Influences on glycerol release, including pH optimum, NaCl inhibition, and activation by serum and heparin are characterized. Two separate assays are described for the measurement of glycerol that yield identical results with nanogram quantities of tissue. The advantage of one assay is its simplicity, while the advantage of the other is that it can be adjusted to measure very small tissue samples (nanogram) with the use of microanalytical procedures (i.e., enzymatic amplification of the NAD+ product of glycerol analysis). Sensitivity of the method is demonstrated by the analysis of triglyceride lipase activity in nanogram samples of single soleus muscle fibers. Measurement of picomole quantities of glycerol produced by lipase activity in single muscle fibers represents at least a 1,000-fold increase in sensitivity compared to currently available methods.

Animals↗
PubMed1986

Chronic stimulation of mammalian muscle: enzyme changes in individual fibers.

Single fibers of rabbit fast-twitch tibialis anterior (TA) muscles were analyzed after continuous low-frequency stimulation for up to 8 wk. After 2-5 wk, every fiber showed higher levels of citrate synthase, hexokinase, and 3-oxoacid CoA-transferase than any control fiber; in some cases these levels were 2-10 times higher (well above any found even in the control soleus, a slow-twitch muscle). Average levels of malate dehydrogenase and alanine transaminase also rose dramatically, but peak single fiber levels were not much above the highest in controls. These differential effects confirm at the single fiber level that chronic stimulation can alter mitochondrial composition. Lactate dehydrogenase, fructose-bisphosphatase, and adenylate kinase declined to levels far below those of any control TA fiber, and, in the case of fructose-bisphosphatase, to within the activity range of control soleus fibers. According to their staining reaction for myofibrillar ATPase, TA fibers were initially 23% type IIA, and 74% type IIB, but by 5 wk these had been converted to a mixture of type I, IIA, and IIC fibers. At 5 wk, levels of lactate dehydrogenase, adenylate kinase, and malate dehydrogenase were characteristic of their (new) ATPase type, but 3-oxoacid CoA transferase had increased to levels 6-15 times higher than in control fibers of the same type.

Adaptation, Physiological↗
PubMed1986

Muscle triglyceride utilization during exercise: effect of training.

The respiratory exchange ratio (RER) is lower during exercise of the same intensity in the trained compared with the untrained state, even though plasma free fatty acids (FFA) and glycerol levels are lower, suggesting reduced availability of plasma FFA. In this context, we evaluated the possibility that lipolysis of muscle triglycerides might be higher in the trained state. Nine adult male subjects performed a prolonged bout of exercise of the same absolute intensity before and after adapting to a strenuous 12-wk program of endurance exercise. The exercise test required 64% of maximum O2 uptake before training. Plasma FFA and glycerol concentrations and RER during the exercise test were lower in the trained than in the untrained state. The proportion of the caloric expenditure derived from fat, calculated from the RER, during the exercise test increased from 35% before training to 57% after training. Muscle glycogen utilization was 41% lower, whereas the decrease in quadriceps muscle triglyceride concentration was roughly twice as great (12.7 +/- 5.5 vs. 26.1 +/- 9.3 mmol/kg dry wt, P less than 0.001) in the trained state. These results suggest that the greater utilization of FFA in the trained state is fueled by increased lipolysis of muscle triglyceride.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1986

Fluorometric procedures for measuring triglyceride concentrations in small amounts of tissue and plasma.

It has been previously shown that triglycerides can be specifically hydrolyzed by lipase from Rhizopus arrhizus in the presence of hog liver esterase and sodium dodecyl sulfate. The glycerol produced can then be measured by sequential reactions with glycerokinase, pyruvate kinase, and lactate dehydrogenase: glycerol and ATP are converted to glycerol-3-phosphate and ADP by glycerokinase; the ADP reacts with phosphoenolpyruvate and pyruvate kinase to yield pyruvate; the pyruvate is converted to lactate with lactate dehydrogenase, and the cofactor NAD+ is simultaneously reduced to NADH. This report describes procedures by which either the disappearance of NADH or the appearance of NAD+ was determined fluorometrically, with 10- to 100-fold greater sensitivity than by spectrophotometry. In addition, enzymatic cycling of NAD+ was used to increase the sensitivity of the assay over 1000-fold, and thereby provided accurate measurement of less than 1 ng of triglyceride. Results obtained from the three fluorometric methods were highly correlated with an automated periodate oxidation method using serum samples and lipid extracts of muscle tissue.

Animals↗
PubMed1986

Uniformity of metabolic enzymes within individual motor units.

Individual muscle fibers of 10 motor units from the tibialis posterior muscle of cat were identified by glycogen depletion techniques, characterized for histochemical type, diameter, and intramuscular locations, and analyzed by quantitative biochemical methods. Four enzymes, representing different energy-yielding pathways, were quantitatively assayed in muscle fibers belonging to motor units selected from each of the three major physiological types. All four enzymes demonstrated identical activities among fibers within a motor unit, while showing up to 11-fold differences among fibers belonging to different motor units. Moreover, fibers within a single motor unit, but of substantially different diameters, were nevertheless homogeneous in specific enzyme activities.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1985

A method for branched-chain amino acid aminotransferase activity in microgram and nanogram tissue samples.

A method for branched-chain amino acid aminotransferase is described which is based on running the reaction in the reverse of the usual direction with glutamate and alpha-ketoisocaproate as substrates. The alpha-ketoglutarate generated is reduced with glutamate dehydrogenase and NADH. For sensitivity in the nanomole range, the NAD+ generated is measured directly by converting to the highly fluorescent strong alkali product. For smaller samples, down to the 0.2- to 2-pmol range, the NAD+ is amplified by enzymatic cycling.

Animals↗
PubMed1985

Control of enzyme activities in individual myotubes cultured without nerve.

The activities of lactate dehydrogenase, malate dehydrogenase, phosphorylase, and adenylate kinase were measured in single myotubes dissected from primary cultures of rat skeletal muscle. For a given enzyme, activities among the spontaneously contracting cells varied as much as eightfold. When the myotubes were paralyzed with tetrodotoxin, the variability in enzyme levels was markedly decreased. These and other findings suggest that differences in enzyme levels among individual myotubes may arise as a result of differences in their pattern of contractile activity.

Adenylate Kinase↗
PubMed1984

Effects of chronic stimulation on the metabolic heterogeneity of the fibre population in rabbit tibialis anterior muscle.

Chronic indirect stimulation (10 Hz) was performed on rabbit tibialis anterior muscle. Long-term stimulation (52-140 days) produced a transformation of the fast tibialis anterior into a slow red muscle as judged from the histochemistry of myofibrillar actomyosin ATPase, the pattern of myosin light chains and the thorough rearrangement of the enzyme activity pattern of energy metabolism. Activity levels of citrate synthetase (CS), malate dehydrogenase (MDH), succinate dehydrogenase (SDH), 3-hydroxy-acyl-CoA dehydrogenase (HAD), and lactate dehydrogenase (LDH) were determined quantitatively by either microbiochemical assays (CS, MDH, HAD and LDH) on microdissected, single fibres or by kinetic microphotometry on cross-sectioned fibres (SDH). The activity profiles of these enzymes displayed pronounced scattering in the fibre population of the unstimulated muscle. Despite a several fold increase in the activities of CS, MDH, SDH and HAD and a pronounced decrease in LDH, chronic stimulation failed to abolish the metabolic heterogeneity of the fibre population. It is possible that chronic indirect stimulation cannot produce uniformity of fibres because of continuing diverse natural activity of the motor units.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1984

Biochemistry of rat single muscle fibres in newly assembled motor units following nerve crush.

A partial crush was applied surgically to the common peroneal nerves of rats, producing motor deficits lasting 4 weeks; the tibialis anterior muscles supplied by the crushed nerves were removed 5 weeks after recovery along with the contralateral control muscles. Myosin ATPase staining following pre-incubation at pH 4.5 was used to determine fibre types and to demonstrate areas of fibre-type grouping in the reinnervated areas of the muscles. Enzyme activities of lactate dehydrogenase (LDH), adenylokinase (AK) and malate dehydrogenase (MDH) were measured using micro-analytical techniques on the individual fibres within the histochemically identical groups and on fibres of the same types selected from areas of the test muscle or the contralateral control which appeared normal. The results show that the degree of enzymatic variation among single fibres reinnervated by a common axon is very small when compared to the general fibre population and, moreover, to fibres of the same histochemical type. Enzyme variability within the newly formed motor units was only slightly greater than the variability reported for normal motor units (Nemeth, Pette & Vrbová, 1981). The results indicate that skeletal muscle fibres originally having great differences in levels of enzyme activity, as demonstrated in the general fibre population, acquire considerable enzymatic similarity following reinnervation by a common motor neurone.

Adenosine Triphosphatases↗
PubMed1984

Myoglobin levels in individual human skeletal muscle fibers of different types.

An attempt was made to determine the relationship of myoglobin content to specific fiber types in human muscle. Biopsies were obtained from biceps brachii, vastus lateralis, and gastrocnemius muscles of untrained subjects and from the vastus lateralis muscle of a highly trained athlete at peak training and at intervals of no training (detraining). Individual muscle fibers were assayed, by quantitative microanalytical methods, for myoglobin, lactate dehydrogenase, malate dehydrogenase, citrate synthase, beta-hydroxyacyl-coenzyme A dehydrogenase, and adenylokinase activities all on the same fiber. The enzyme levels were used to classify the fibers into type I or II. The results show that the content of myoglobin in human muscle does not differ greatly between fiber types in contrast to other species. The type II fibers contained, on the average, at least two-thirds as much myoglobin as type I fibers. The concentration of myoglobin did not change in either fiber type during detraining (84 days), despite marked changes in lactate dehydrogenase, adenylokinase and the three oxidative enzymes.

Adenylate Kinase↗
PubMed1983

Failure of endurance training to alter the cardiovascular response to static contraction.

The purpose of this study was to determine whether endurance training alters the cardiovascular response to static contractions of the trained, but not untrained, musculature. Six healthy, untrained males (aged 23-36 years) underwent 10-12 weeks of intensive training involving both cycling and running. Peak VO2 on the bicycle ergometer, VO2max during graded treadmill running and concentrations of citrate synthase (CS) and malate dehydrogenase (MDH) in the vastus lateralis muscle were measured before and after training. Subjects performed static leg extension and forearm extension at 30% of maximal voluntary contraction until exhaustion before and after training. Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure were measured at rest, and in addition to perceived exertion (PE), every 30 s during contraction. Endurance training elicited significant increases in peak VO2 (36%), VO2max (32%), CS (25%) and MDH (42%) (all P less than 0.05). HR at rest was significantly lower (P less than 0.05) after training, while SBP and DBP were unchanged. HR, SBP, DBP and PE increased throughout both types of static contractions. However, the magnitude of the increases were unaffected by training. In contrast to recent findings, these results suggest that the increases in heart rate and blood pressure in response to static contraction are not altered after endurance training in either the trained or the untrained muscle groups.

Adult↗
PubMed1983

Effects of detraining on enzymes of energy metabolism in individual human muscle fibers.

Muscle biopsies were obtained from three cyclists and four runners at the end of 10-24 mo of intensive training and after intervals of detraining up to 12 wk. Control samples came from four untrained persons and four former athletes. Macro mixed fiber samples were assayed for lactate dehydrogenase, adenylate kinase, glycogen phosphorylase, citrate synthase, malate dehydrogenase, beta-hydroxyacyl-CoA dehydrogenase, succinate dehydrogenase, beta-hydroxybutyrate dehydrogenase, creatine kinase, hexokinase, 1-phosphofructokinase, fructosebisphosphatase, protein, and total creatine. In the case of three trained persons and two controls, the first six of the enzymes were also measured in individual fibers. Before detraining, enzymes of oxidative metabolism were substantially higher than in controls, and differences in levels between type I and type II fibers were smaller. During detraining, oxidative enzymes were decreased in both fiber types but the type II fibers did not fall to control levels even after 12 wk. Phosphorylase increased with detraining in both fiber types. The same is true for lactate dehydrogenase and adenylate kinase, except in the case of the type I fibers of one individual. Among the other six enzymes (measured in mixed fiber samples), only hexokinase was consistently affected (decreased) by detraining.

Adenylate Kinase↗
PubMed1982

Electrical stimulation of denervated muscle prevents decreases in oxidative enzymes.

The influence of muscular contraction on the oxidative enzymes and the diameters of muscle fibers was investigated. Soleus muscles of guinea pigs were denervated for four weeks. The denervated fibers showed a reduction in the intensity of staining for beta-hydroxybutyrate dehydrogenase, cytochrome oxidase, succinate dehydrogenase, and NADH-dependent tetrazolium reductase. Denervation also resulted in a decrease in fiber diameter. Denervated soleus muscles were electrically stimulated to contract over a four-week period at a frequency normally received by slow contracting muscles. Electrical stimulation caused the stain intensity of histochemical reactions for oxidative enzymes to appear to be normal or greater than normal in 90% of the denervated fibers. Stimulation also caused 69% of the denervated fibers to be of normal or greater than normal size. The results demonstrate that contraction of denervated muscle by electrical stimulation prevents the loss of oxidative enzymes and the atrophy associated with denervation.

Adenosine Triphosphatases↗
PubMed1981

Comparison of enzyme activities among single muscle fibres within defined motor units.

1. Muscle fibres from single motor units of rat extensor digitorum longus were depleted of their glycogen by electrical stimulation and identified by the periodic acid-Schiff stain after treatment in a medium that selectively enhanced glycogen content in the non-depleted fibres. 2. Malate dehydrogenase (MDH) and fructose-1,6-diphosphatase (FDPase) activities were studied quantitatively in single dissected fibres of individual motor units and in fibres selected randomly from the same muscle. 3. In contrast to the large variability of MDH and FDPase in muscle fibres taken randomly, the muscle fibres from the same motor units had similar enzyme activities. 4. The resistance to fatigue of the motor units correlated well with the capacity of aerobic oxidative metabolism, as judged by the activity of MDH in the muscle fibres.

Animals↗
PubMed1980

Effects of denervation and simple disuse on rates of oxidation and on activities of four mitochondrial enzymes in type I muscle.

To differentiate the effect of muscle contractile activity from that of motor nerve on oxidative processes in type I muscle, oxidative processes were studied in muscle after immobilization and after denervation. The two processes led to similar atrophy of muscle weight and of the mean diameter of muscle fibers. Disuse of soleus muscle (type I) did not affect rates of oxidation of 14C-labeled substrates although these were reduced by disuse of the vastus lateralis (type II). Disuse of the soleus did not affect activities of several mitochondrial enzymes assayed by histochemical or biochemical methods. However, denervation of the soleus did lead to a fall in metabolic rates and enzyme activities. The activity of 3-hydroxybutyrate dehydrogenase fell more than did the activities of succinic dehydrogenase, lipoamide dehydrogenase, or cytochrome-c oxidase in both homogenates and in mitochondrial fractions. These results suggest nerve may regulate mitochondrial enzymes in type I muscle. The mechanism appears to be different from that which regulates oxidative processes in type II muscle.

Animals↗