Chronic and acute exercise do not alter Ca2+ regulatory systems and ectonucleotidase activities in rat heart

The purpose of this investigation was to examine the effects of chronic and acute exercise on the main components involved in excitation-contraction c oupling and relaxation in rat heart. Sixty male Wistar rats were divided in to a sedentary (S) and three 12-wk treadmill-trained groups (T-l, moderate intensity; T-2, high intensity; T-3, interval running). After 12-wk, 15 rat s from the S group and 15 rats from the T-2 group were subjected to a singl e treadmill-exercise session until exhaustion before being killed at 0, 24, or 48 h (acute exercise). The remaining animals were killed 48 h after the last standard exercise session (chronic exercise). The efficacy of the tra ining programs was confirmed by an increase in treadmill endurance time and in skeletal muscle citrate synthase activity. None of the exercise program s modified heart weight or cardiac oxidative capacity. [H-3]PN200-110 and [ H-3]ryanodine binding to cardiac homogenates indicated that the density of L-type and sarcoplasmic reticulum (SR) Ca2+ channels was the same in S and trained rats. The SR Ca2+-ATPase activity was also unmodified. Finally, the activities of the ectoenzymes Mg2+-ATPase and 5'-nucleotidase, which are i nvolved in degradation of extracellular nucleotides, were not affected by e ither of the running programs. After the acute exercise session, no changes were detected in either of the tested parameters in heart homogenates of S and T-2 animals. We conclude that neither treadmill-exercise training for 12 wk nor exhaustive exercise alters the density of Ca2+ channels involved in excitation-contraction coupling or the SR Ca2+-ATPase and the ectonucleo tidase activities in rat heart.