ROLE OF SODIUM-HYDROGEN EXCHANGE IN THE PROLIFERATION OF IMMORTALIZED LYMPHOBLASTS FROM PATIENTS WITH ESSENTIAL-HYPERTENSION AND NORMOTENSIVE SUBJECTS

Objective: The aim was to investigate the effect of ethylisopropylamiloride (EIPA), an inhibitor of Na+/H+ exchange, and of extracellular pH on the proliferation of immortalised lymphoblasts derived from patients with essential hypertension and normotensive controls. Methods: Na+/H+ exchange activity was determined in cells loaded with the fluorescent pH indicator BCECF Cell proliferation was determined by FAGS analysis, by cell counting, and from the incorporation of [H-3]-thymidine. Results: EIPA inhibited the Na+/H+ exchanger with an average K-I value of 14 nM in all cell lines. Cell growth and DNA synthesis were only inhibited at EIPA concentrations > 10 mu M suggesting a non-specific effect independent of Na+/H+ exchanger blockade. When extracellular pH was varied from 7.1 to 7.7 by changing the HCO3- concentration at constant PCO2, cell proliferation was optimal at pH 7.4, but reduced at acidic and alkaline pH in cells from normotensive and hypertensive subjects. The increased proliferation of lymphoblasts from hypertensive subjects persisted over the whole pH range. Comparable results were obtained when pH was altered by varying the PCO2 at constant HCO3-. Preincubation of cells with pertussis toxin inhibited serum stimulated DNA synthesis by 14.5% and 23.5% (P=0.02) in cell lines from normotensive and hypertensive subjects. Conclusions: The enhanced Na+/H+ exchanger activity in lymphoblasts from patients with essential hypertension is obviously not the major determinant of the enhanced proliferation of these cells. The increased sensitivity of the growth of ''hypersensitive'' cell lines to pertussis toxin suggests a cellular alteration which resides upstream of Na+/H+ exchange activity and proliferation control.