Metabolic effects of ouabain in the perfused rat heart

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Abstract
Ouabain increased the uptake and oxidation of glucose-U-C14 by perfused guinea pig and rat hearts by 50%. Cardiac glycogen content remained constant and no change in glycogen specific activity was observed. The metabolic changes produced by ouabain were dependent on the calcium concentration of the perfusate. Reduction of the calcium content of the perfusate by 50% abolished the increase in C14O2 production by ouabain. The C14O2 production of hearts perfused with buffer containing twice the physiological calcium concentration was similar to that of hearts perfused with buffer containing the normal calcium concentration and ouabain. The effect of the high calcium concentration combined with ouabain was not different from that produced by either one alone. Steady-state levels of glycolytic intermediates after a 30-min perfusion period were elevated in the absence of glycogenolysis and free glucose did not accumulate intracellularly. In so far as the changes in glucose metabolism are concerned the findings are consistent with the concept that the effects of glycosides on cardiac muscle are dependent on changes in calcium transport or concentration at the site of the contractile elements.