Exercise training alters Ca release from coronary smooth muscle sarcoplasmic reticulum

We examined intracellular free calcium (Cai) buffering by the sarcoplasmic reticulum (SR) of porcine coronary artery smooth muscle cells (SMC) and the effects of chronic exercise training (ET) on this phenomenon. Cai was measured with fura-2. Depolarization of single SMC via high extracellular K induced the entry of Ca, a fraction of which was sequestered (buffered) by the SR. Endurance ET of Yucatan minipigs for 16-20 wk increased exercise tolerance, heart-to-body weight ratios, and skeletal muscle oxidative capacity. Caffeine-induced Ca release from the SR after a short (2 min) recovery time from depolarization to caffeine exposure was equal in SMC from both ET and sedentary pigs. With a longer (11 min) recovery period after depolarization, caffeine-induced Ca release from the SR of sedentary pigs was equal to that after the short recovery time. However, after the long recovery, caffeine-induced Ca release in SMC of ET pigs was 60% less (P less than 0.05) than in the other protocols. These results indicate that chronic ET increased Cai buffering in SMC of the coronary artery by increasing the rate of spontaneous Ca extrusion from the SR.