Erythrocyte Sodium and Potassium in Patients with Hypokalaemia

Abstract

The erythrocyte content of Na and of K were measured in 231 unselected patients with hypokalemia, and together with net ouabain-sensitive sodium efflux in patients with severe hypokalemia, before (20 patients) and during K repletion (14 patients). The erythrocytes of the patients with hypokalemia compared with control subjects had on average an increase in Na content, a decrease in K content and a reduction in the rate constant of ouabain-sensitive Na efflux. All 3 changes had a similar curvilinear relation to the concentration of K in plasma with relatively little change in the measured variable unless the plasma K was very low. There was a similar curvillinear relation between the final Na and K content of normal erythrocytes and the K concentration of the medium in which they were incubated for 48 h in vitro. Evidently, the changes in the Na and K content of erythrocytes in hypokalemia are due to a direct inhibiting effect of the hypokalemia on the activity of the Na pump. In many patients with hypokalemia of moderate degree the increase in erythrocyte Na content was less than expected from the effect in vitro of a low extracellular K concentration. Apparently, a compensatory change, presumably an increase in the number of Na pumps, is a common event even in moderate hypokalemia.