Insulin action on cardiac glucose transport Studies on the role of the Na +/K + pump

Abstract

Isolated muscle cells from adult rat heart have been used to study the relationship between myocardial glucose transport and the activity of the Na +/K + pump. 86Rb +-uptake by cardiac cells was found to be linear up to 2 min with a steady-state reached by 40–60 min, and was used to monitor the activity of the Na +/K + pump. Ouabain (10 −3 mol/I) inhibited the steady-state uptake of 86Rb + by more than 90%. Both, the ouabain-sensitive and ouabain-insensitive 86Rb +-uptake by cardiac cells were found to be unaffected by insulin treatment under conditions where a significant stimulation of 3- O-methylglucose transport occurred. 86Rb +-uptake was markedly reduced by the presence of calcium and/or magnesium, but remained unresponsive towards insulin treatment. Inhibition of the Na +/K + pump activity by ouabain and a concomitant shift in the intracellular Na +:K + ratio did not affect basal or insulin stimulated rates of 3- O-methylglucose transport in cardiac myocytes. The data argue against a functional relationship between the myocardial Na +/K + pump and the glucose transport system.