Exercise In Rat Skeletal Muscle Research Articles

Superoxide dismutase gene expression is activated by a single bout of exercise in rat skeletal muscle.

The goal of this experiment was to examine contraction-mediated activation of superoxide dismutase (SOD) gene expression in rat superficial vastus lateralis (SVL, type IIb) and deep vastus lateralis (DVL, type IIa) muscles. Female Sprague-Dawley rats were randomly divided into exercise (E) and control (C) groups that were sacrificed at 0, 1, 2, 4, 10, 24, and 48 h (n=6) following an acute bout of treadmill exercise (25 m/min, 5% grade) to exhaustion (running time approximately equals 1 h). Nuclear factor-kappaB (NF-kappaB) in DVL and SVL showed maximal binding at 2 and 10 h respectively, and remained elevated. Activator protein-1 (AP-1) showed maximal binding at 1 h post-exercise, and returned to resting levels at 10 h in both muscles. Mn SOD mRNA abundance in the DVL was increased at 0 (P<0.01), 1, and 2 h (P<0.05) post-exercise, whereas Mn SOD protein was unchanged. In SVL, Mn SOD mRNA abundance was not altered by exercise, whereas Mn SOD protein content was increased at 10 (P<0.05) and 24 h (P<0.075) post-exercise. CuZn SOD mRNA was unchanged with exercise in DVL and SVL, but CuZn SOD protein was elevated 48 h after exercise in both DVL and SVL (P<0.01). Activities of Mn SOD, CuZn SOD and total SOD showed no change with exercise in either muscle examined. These findings indicate that an acute bout of exercise can increase binding of NF-kappaB and AP-1 in both SVL and DVL, which may stimulate Mn SOD mRNA transcription in the more oxidative type DVL muscle. The increased CuZn SOD protein contents seen post-exercise, without increases in mRNA abundance in both DVL and SVL, suggest a translational mechanism in this SOD isoform.

Absence of an effect of fatigue on muscle efficiency during high-intensity exercise in rat skeletal muscle.

The effect of fatigue was studied on rat skeletal muscle efficiency during maximal dynamic exercise of 10s duration. After the initial 4s of exercise, power output decreased rapidly to 46.2 +/- 6.7% (mean +/- SD; n = 6) after 6s of stimulation and further to 17.5 +/- 5.8% in the last contraction. Both the rates of total work output and high-energy phosphate consumption decreased with increasing exercise duration. As a result muscle efficiency was not affected by exercise time in the present experiments. This result indicates that fatigue in severe maximal exercise is induced by a feed-back mechanism, which in the case of high ATP utilisation rates will reduce ATP splitting probably by reducing Ca(2+)-release from the sarcoplasmic reticulum.

A linear relationship between ATP degradation and fatigue during high‐intensity dynamic exercise in rat skeletal muscle

The relationship between changes in work output (fatigue) and metabolite concentrations was measured in rat skeletal muscle during the course of dynamic exercise (10 s). After 4 s, work output decreased rapidly to approximately 30% at 8 s. In contrast to the changes in phosphocreatine and lactate, the change in ATP concentration paralleled the reduction in work output. A strong linear relationship (r = 0.95) was found between the relative decrease in ATP and the extent of fatigue. Possible mechanisms underlying this relationship are discussed.

Beta-adrenergic receptors are not responsible for exercise stimulation of glucose transport

This study was designed to examine whether the increased glucose transport after acute exercise in rat skeletal muscle is mediated via beta-adrenergic receptor stimulation. Sarcolemmal (SL) membranes were isolated from three groups: control (C), acute exercise (E), and exercise + propranolol (E+P). The acute exercise bout was performed on a treadmill and consisted of a 45-min run until near exhaustion. E+P received an intravenous propranolol injection (0.8 mg/kg) 10 min before the exercise session. Michaelis-Menten kinetics at 1.5 s indicated that the Vmax for glucose transport was increased after each perturbation compared with C but were not different from each other (E, 4,334 +/- 377; E+P, 4,824 +/- 357; and C, 1,366 +/- 124 pmol.mg protein-1.s-1). The apparent Km's were similar in all groups. Scatchard plots for the D-glucose inhibitable class of cytochalasin B binding sites indicated no differences in either the total number of binding sites in the SL vesicles (C, 5.5 +/- 0.3; E, 5.1 +/- 0.2, and E+P, 5.1 +/- 0.3 pmol/mg protein) or in their dissociation constant (Kd) (C, 46 +/- 3; E, 48 +/- 3; and E+P, 49 +/- 2 nM). The increase in Vmax for transport was similar between E and E+P, indicating that exercise does not stimulate glucose transport via the beta-adrenergic receptor.

Enzymatic down regulation with exercise in rat skeletal muscle

Maximal activities of rat skeletal muscle mitochondrial citrate synthase (CS), malate dehydrogenase (MDH), and alanine aminotransferase (ALT), as well as several other mitochondrial enzymes involved in various metabolic functions were significantly suppressed after a single bout of acute or exhaustive treadmill running. This enzymatic “down regulation” was maintained 24 and 48 h post exhaustion, especially in the untrained rats. Neither muscle cytosolic nor hepatic enzymes exhibited down regulation after exercise. Proteolysis was increased with exercise as assessed by the clearance of [ 3H]leucine previously incorporated into the proteins of the rats. Decreased CS, MDH, and ALT activities correlated with a significant loss of mitochondrial total protein sulfhydryl ( r = 0.67,0.68,0.59, respectively, P< 0.001) in untrained rats and both CS and MDH could be partially restored by incubation with dithiothreitol. Endurance-tested untrained and trained rats had significantly higher glutathione peroxidase (GPX) activity in both muscle mitochondria and cytosol which correlated significantly with endurance time ( r = 0.70 and 0.74, respectively). It is concluded that enzymatic down regulation is not caused by proteolysis alone; i.e., peroxides and oxygen free radicals produced in prolonged exercise may alter the intramitochondrial redox state by oxidizing free thiols that may be required at active sites of these enzymes. Training may enhance the ability of the muscle to resist the toxic oxygen species by increasing GPX activity.