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

Abstract

SUMMARY Alterations in red blood cell (RBC) Na + ,K + pump and in Na + ,K + cotransport (CoT) have been described in essential hypertension (EH). We examined pump and CoT in 50 normotensive (NT) subjects and 58 EH subjects subdivided by race and family history of hypertension (+ FH). RBCs were preloaded with Na + to obtain intracellular levels of 25 mM/liter 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/liter cells/hr) compared to those without + FH. A subgroup of Caucasian EH subjects displayed high CoT (>0.6 mM/liter cells/hr); 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 sodium 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 RBCs from black and Caucasian NT and HT subjects. Since CoT function is normally low in RBCs 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. (Hypertension 6: 536-544, 1984)

Kinetic analysis of erythrocyte Na+-K+ pump and cotransport in essential hypertension.

“…We previously reported lower mean levels of RBC outward Na + -K + cotransport in black normotensive and hypertensive subjects as compared with whites and no effect of family history of hypertension on cotransport function in blacks. 24 Our current results extend these observations to examine kinetic mechanisms for differences in cotransport function between blacks and whites. Examination of the range of kinetic curves for cotransport-mediated Na efflux in blacks revealed a trend toward lower V^, values as compared with whites, especially in hypertensive subjects.…”

“…The majority of subjects in this study were included in a previous study examining RBC Na + -K + cotransport and pump in cells loaded by the 2,5-p-chloromercuribenzenesulfonic acid (PCMBS) method to a single Naj concentration at approximately 25 mmol/L cells. 24 Fresh venous blood was collected between 0800 and 1000 in chilled, heparinized tubes and centrifuged at 3,000 g, and the plasma and buffy coat were removed by aspiration. RBCs were washed four times with a washing solution containing 152 raM choline chloride, 1 mM MgCl 2 .…”

“…34 " 36 We previously reported no difference in ouabain-sensitive Na efflux rates in RBCs frorn black and white normotensive and hypertensive subjects examined at one level of Na, (25 mmol/L cells). 24 We now expand these findings to examine RBC Na + -K + pump capacity over a wide range of Na, in order to compare kinetic parameters in the four study groups. There were no major differences between K o 5 and V,f or ouabain-sensitive Na efflux in RBCs from black versus white subjects or in normotensive versus essential hypertensive subjects.…”

“…24 In contrast, RBC Na + -K + cotransport was low in black normotensive and hypertensive subjects compared with white hypertensive patients. The present study represents an extension of these observations to examine the kinetic mechanism for these findings.…”

Kinetic Parameters of Rubidium Transport Pathways Are Normal in Cystic Fibrosis Red Cells

“…Interindividual variability in the measurements of Km and V, , , of the NaK cotransport system was much greater than those of NaK pump activity, consistent with the observations in studies of larger populations (22)(23)(24). Although the Co V, , , for Rb was slightly lower and the Km was slightly higher in CF RBC (Table I), these differences were not statistically significant.…”