EFFECTS OF EXHAUSTIVE EXERCISE ON SARCOPLASMIC RETICULUM ATPase : COMPARISON OF SHORT- AND LONG-TERM EXERCISE

Effects of short-term, high-intensity and long-term, moderate-intensity exercise on biochemically assessed asrcoplasmic reticulum(SR)ATPase protein were analyzed in muscle homogenates of the rat after treadmill runs to exhaustion(avg.time to exhaustion 2min 48sec and 1h 29min, respectively). The exercise-induced changes in SR Ca^<2+>-ATPase activity were muscle type-specific. After short-term exercise, a decrease in the activity occurred in the soleus muscle and the super-ficial region of the vastus lateralis muscle whereas long-term exercise depressed the rate of ATP hydrolysis in the soleus muscle and the deep region of the vastus lateralis muscle. The concentration of fluorescein isothiocyanate, a competitor at the ATP-binding site, for 50% inhibition of SR Ca^<2+>-ATPase activity fluctuated only in the soleus muscle subjected to short-term exercise;it was increased by 31%. This change occurring in the soleus muscle would elevate SR Ca^<2+>-ATPase activity at a given concentration of ATP. The results presented here suggest that acute short-term exercise to exhaustion may exert a remarkably inhibitory factor on SR Ca^<2+>-ATPase protein of slow-twitch muscle, which can overcome the positive effect probably arising from the phosphorylation of the phospholamban