Structure and function of cardiac mitochondria in exhausted guinea pigs

The ultrastructure and functional capacity of mitochondria from hearts of exhausted guinea pigs were compared to those from rested animals. Electron micrographs of heart ventricles were examined for ultrastructural alterations, and functional capacity was studied by oxygen polarography. General swelling of mitochondria from exhausted animals was indicated by a 41% reduction in mitochondrial surface/volume ratio and a 22% increase in volume density of mitochondria from exercised animals when compared to those from controls. The yield of isolated mitochondria from exhausted guinea pigs was similar to that for control animals. In the presence of all substrates tested the rate of oxygen consumption was lower in the exhausted animals than in the controls. The ADP/O ratios and respiratory control indices for pyruvate, succinate and ascorbate were not systematically affected by exercise. With glutamate as substrate respiratory control was reduced in exercised guinea pigs. These experiments suggest that the structure of myocardial mitochondria from exhausted animals is sufficient to maintain normal ADP/O ratios but is not adequate to maintain normal rates of respiration.