Substrate utilization of adult cardiac myocytes.

Cultured adult myocytes are in a state of basal metabolism. When glucose is the only exogenous substrate, they produce lactate over CO2 at a constant rate of 2.7 from this substrate. Increase of oxygen tension does not change this behaviour. Insulin preferentially increases lactate formation, dichloroacetate only CO2 production. The fact that the lactate/CO2 ratio can be varied from 0.5 to 16 indicates that there is no close coupling between glycolytic flux and pyruvate oxidation. Both exogenous lactate and fatty acids are used preferentially over glucose. But increase of fatty acid oxidation and inhibition of glucose oxidation are not complementary. Glycolytic flux is only slightly decreased when fatty acid oxidation is already saturated. The results indicate that fatty acids interact with glucose oxidation primarily by inactivation of the pyruvate dehydrogenase. Neither insulin nor dichloroacetate in the presence of glucose inhibit fatty acid oxidation.