Pyruvate transport and pyruvate dehydrogenase activity in isolated cardiac mitochondria exhibiting dissimilar oxygen consumption rates from two species of amphibian, Bufo marinus and Rana catesbeiana

Abstract

Cardiac mitochondria were isolated from two species of amphibian (Bufo marinus and Rana catesbeiana), whose cardiovascular systems are adapted to either predominantly aerobic or glycolytic modes of locomotion, exhibited considerable differences in oxidative capacity. Mitochondrial oxidative capacity was compared using VO2 max and respiratory control ratios (RCR) in the presence of pyruvate and ADP. Bufo cardiac mitochondria exhibited VO2 max values twice that of Rana cardiac mitochondria at neutral pH. Biochemical bases of differences in oxidative capacity were sought at the level of pyruvate transport and pyruvate dehydrogenase activities. Pyruvate transport was measured via a radiolabeled-tracer assay in isolated Bufo and Rana cardiac mitochondria. Time-course experiments indicated the presence of an ?-cyano-4- hydroxycinnamate-sensitive pyruvate uptake mechanism in both species. Kinetic constants were dissimilar between the two species with Bufo exhibiting a greater Kt and Jmax. Other carboxylates including lactate, competed strongly with pyruvate indicating a broad substrate specificity for this mitochondrial transporter. Pyruvate uptake was also shown to decrease as a function of decreasing extramitochondrial pH. In addition, pyruvate dehydrogenase (PDH) activity was higher in toad mitochondria relative to frog. Differences in amphibian cardiac mitochondria pyruvate transport and PDH activity were found to correlate with interspecific variation in mitochondrial VO2 max.