Erythrocyte Na+,K+ cotransport and Na+,K+ pump in black and caucasian hypertensive patients.

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Abstract
Alterations in red blood cell (RBC) Na+, K+ pump and in Na+, K+ cotransport (CoT) have been described in essential hypertension (EH). Pump and CoT were examined in 50 normotensive (NT) subjects and 58 EH subjects, subdivided by race and family history of hypertension (+FH). RBC were preloaded with Na+ to obtain intracellular levels of 25 mM/l cells by using the p-chloromercuribenzene sulfonic acid (pCMBS) method. Na+ and K+ efflux rates into a magnesium-sucrose medium were quantitated in the presence of ouabain and ouabain plus furosemide to define pump and CoT activity, respectively. Mean intracellular Na+ content was higher (P < 0.05) in Black NT and HT subjects, compared to Caucasians. Mean RBC CoT was lower in Black EH compared to NT and compared to Caucasian NT and HT subjects. Conversely, Caucasian HT patients had higher mean CoT than NT subjects. Subdivision into +FH revealed very little effect of +FH on CoT in Black NT and HT subjects. In Caucasian NT and HT subjects with +FH, mean CoT was significantly reduced (< 0.3 mM/l cells/h), compared to those without +FH. A subgroup of Caucasian EH subjects displayed high CoT (> 0.6 mM/l cells/h); a +FH had little impact on the high CoT group. There was no correlation between RBC CoT activity and age, sex, severity of hypertension, urinary Na excretion and plasma aldosterone. There was a positive correlation (r = +0.47; P < 0.01) between CoT and upright plasma renin activity. In 11 EH patients, reductions in blood pressure by antihypertensive agents did not consistently alter RBC CoT activity. Mean Na+ efflux by the RBC Na+, K+ pump measured in washed cells at Vmax was not different in RBC from Black and Caucasian NT and HT subjects. Since CoT function is normally low in RBC from both Black NT and EH subjects, the CoT assay may not be useful as a screening test to identify hypertensive-prone Black NT subjects. In Caucasian subjects with a +FH, the assay might have utility as a screening procedure if further evidence links this assay to the pathophysiology of EH.