CANINE CARDIAC SARCOPLASMIC-RETICULUM IS NOT ALTERED WITH ENDURANCE EXERCISE TRAINING

To investigate the effect of exercise training on calcium movements by isolated cardiac sarcoplasmic reticulum (SR), mongrel dogs either rem ained sedentary (S) or were exercise-trained (E) via running for a per iod of 8-10 wk. The trained state was confirmed by the increase in ske letal muscle citrate synthase activity and decreases in submaximal exe rcise heart rates in the E group but not in the S dogs. The properties of isolated cardiac SR were identical between the groups. The variabl es tested included ATP-dependent calcium transport and calcium-stimula ted ATPase activity. Importantly, there was no difference in spontaneo us calcium release which occurred after peak ATP-dependent calcium acc umulation was reached. Calcium release from passively loaded vesicles induced by calcium and ionophore also did not differ in the SR isolate d from the E dogs. The change in the affinity of the SR CaATPase for c alcium after the addition of the polyanion, heparin, was similar in bo th groups, indicating that the regulation of calcium-stimulated ATPase activity by the SR protein, phospholamban, is not modified by exercis e training. We conclude that exercise training of 8-10 wk duration doe s not alter the calcium handling properties of cardiac SR isolated fro m mongrel dogs.