Oxidative capacity distribution in the cardiac myocytes of hypermetabolic rats

To study the distribution of oxidative capacity in the cardiac myocyte in control and in hypermetabolic (hyperthyroid) rats, we evaluated mitochondrial volume density (Vv,mi) distribution by morphometry and oxidative capacity, cytochrome a + a3 concentration and protein yield of isolated subsarcolemmal and interfibrillar mitochondria by biochemical techniques. In control animals Vv,mi underneath the sarcolemma was higher than in the center of the myocytes and it decreased linearly with increasing distance from the capillaries. Interfibrillar mitochondria showed a greater oxidative capacity and a high concentration of cytochrome a + a3 than subsarcolemmal mitochondria. Values of Vv,mi and its distribution were not changed by the hypermetabolic condition. Oxidative capacity and cytochrome a + a3 concentration were higher in the interfibrillar mitochondria but not in the subsarcolemmal mitochondria of the hypermetabolic rats. The product of the oxidative capacity of the mitochondria times the Vv,mi indicated that the oxidative capacity of the interfibrillar zone is 30% higher than that of the subsarcolemmal zone. In the hypermetabolic rats, due to the increase in oxidative capacity of the interfibrillar mitochondria, the oxidative capacity of this zone was 80% higher than that of the subsarcolemmal zone.