Outward Na+-K+-Cl- cotransport function in erythrocytes from essential hypertensives

We have performed a kinetic analysis of the interaction of the outward Na+-K+-Cl- cotransport system with intra-cellular Na+ in erythrocytes from 30 normotensive controls and 72 patients with essential hypertension. Neither maximal rate of ouabain-resistant, bumetanide-sensitive sodium efflux (Vmax) nor intracellular Na+ content required for half-maximal stimulation (K50%) were significantly different between normotensives and hypertensives. Nevertheless, using 95% confidence limits of the K50% in the normotensive group as a cut-off point, 21 (29.17%) essential hypertensive patients exhibited values above the upper normal limit of 20.11 mmol/l cells, revealing a decreased apparent affinity of outward Na+-K+-Cl- cotransport for internal Na+ ('Co-' hypertensives). The Vmax of Na+-K+-Cl- cotransport exhibited a great variability among hypertensives but 'Co-' patients tended to have increased values of this parameter when compared with the remaining essential hypertensives (959 +/- 84 vs 652 +/- 39 mumol/l cells/h, P = 0.0024). Mean BP values were significantly lower in the 'Co-' subset (121.4 +/- 1.6 mmHg), compared with the remaining 51 hypertensive patients (126.4 +/- 1.3 mmHg, P = 0.0297). We conclude that an abnormal function of outward Na+-K+-Cl- cotransport is present in 19% to 40% of Spanish patients with essential hypertension and this abnormality may be implicated in the mechanisms of hypertension.