Intracellular Potassium

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Abstract
Normal human red cells which have had their intracellular sodium (Nac) reduced have a diminished Na-K pump rate, but only if intracellular potassium (Kc) is high. If most of the Kc is replaced by tetramethylammonium or choline, both ouabain-sensitive Na efflux and K influx are significantly increased even with Nac below normal. Cells with reduced Nac and high Kc have an unchanged Na efflux if external potassium (Kext) is removed. In contrast, low-Na, low-K cells have a large ouabain-sensitive Na efflux which shows a normal response to removal of Kext. Neither low-K nor high-K cells have an altered ouabain-sensitive K efflux. Measurement at constant low Nac and varying Kc shows the pump Na efflux to be an inverse function of Kc. Thus, in low-Na cells, Kc appears to act as an inhibitor of the pump. Inhibition by high Kc can be seen even when Nac is normal. The effects attributed to Kc are distinguished experimentally from other variables such as cell volume, adenosine triphosphate concentration, effects of the replacement cations, and the method used to alter intracellular cation concentrations. A role is proposed for Kc, in cooperation with Nac, in regulating the pump rate of normal human red cells.

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