Porcine cardiac myocyte power output is increased after chronic exercise training

Chronic exercise training increases the functional capacity of the heart, perhaps by increased myocyte contractile function, as has been observed in rodent exercise models. We examined whether cardiac myocyte function is enhanced after chronic exercise training in Yucatan miniature swine, whose heart characteristics are similar to humans. Animals were designated as either sedentary (Sed), i.e., cage confined, or exercise trained (Ex), i.e., underwent 16-20 wk of progressive treadmill training. Exercise training efficacy was shown with significantly increased heart weight-to-body weight ratios, skeletal muscle citrate synthase activity, and exercise tolerance. Force-velocity properties were measured by attaching skinned cardiac myocytes between a force transducer and position motor, and shortening velocities were measured over a range of loads during maximal Ca2+ activation. Myocytes (n = 9) from nine Ex pigs had comparable force production but a approximately 30% increase in peak power output compared with myocytes (n = 8) from eight Sed. Interestingly, Ex myofibrillar samples also had higher baseline PKA-induced phosphorylation levels of cardiac troponin I, which may contribute to the increase in power. Overall, these results suggest that enhanced power-generating capacity of porcine cardiac myofibrils contributes to improved cardiac function after chronic exercise training.