REGULATION OF SUGAR-TRANSPORT IN THE MYOCARDIUM - EFFECTS OF OUABAIN IN RESTING AND BEATING ISOLATED GUINEA-PIG LEFT ATRIA

The effect of ouabain on sugar transport in quiescent beating guinea pig left atria was studied by measuring the tissue/medium distribution of 3-methylglucose. The data were correlated with simultaneously measured changes in intracellular Na+ and K+ and in contractile force. In resting atria, as in other types of muscle, sugar transport paralleled internal Na+, both being decreased by low (10-9 g/ml) and increased by high (10-5 g/ml) ouabain. In atria contracting at 75 beat/min there was an additional stimulating effect of ouabain which closely followed the positive inotropic effect of the drug, with maximal increase in sugar transport and contractile force around 10-6 g/ml. Higher concentrations elicited contracture, and sugar transport was decreased to the level seen in resting tissues. Changes in Na+ and K+ were the same as in resting atria and did not reflect the inotropic effect of ouabain. As changes in Ca2+ distribution and fluxes result from both alterations in contractile force and in internal Na+ level (via Ca2+-Na+ exchange), the effects of ouabain on sugar transport are consistent with the hypothesis that regulation of sugar transport in muscle is mediated by the availability of cytoplasmic Ca2+ for binding to a regulatory site. © 1979.