Altered erythrocyte cation transport related to hypertension or oral contraception

Intracellular cation concentrations (Nai, Ki), and the influx of Rb86 and of Na22 were measured in the erythrocytes of 22 normal women with no family history of hypertension, 16 women with untreated essential hypertension, and 14 normotensive women treated with hormonal contraceptives. Values for total Rb influx, and for its components denoting sodium pump activity (ouabain-sensitive) and Na, K co-transport (ouabain-resistant, frusemide-sensitive), were significantly greater in the hypertensive and contraceptive-treated groups than in the normal group. Na, K cotransport measured by Na influx (frusemide-sensitive) was found to be significantly increased in the contraceptive-treated but not the hypertensive group. Passive sodium diffusion (frusemide-resistant Na influx) and Ki did not differ significantly between groups. Nai was lower in the hypertensive group than in the other two groups. These findings support the hypothesis that hypertension or hormonal contraception are associated with increased leakage of K ions from erythrocytes, without a corresponding increase in passive Na influx: the change in cell membrane permeability is compensated for by increases in Na, K co-transport and sodium pump activity, adjusted to allow for altered differential permeability to K and Na ions.