Nongenomic Effect of Aldosterone on Ion Transport Pathways of Red Blood Cells

Abstract

The direct influence of aldosterone on the human and avian red blood cell (RBC) transport systems, Na⁺/K⁺ pump, Na⁺,K⁺,2Cl^- symporter, and K⁺ (Na⁺)/H⁺ exchanger, was investigated with tracer kinetics. The present work proved that aldosterone has no significant effect on these transport pathways. However, in young human RBCs containing reticulocytes aldosterone showed a significant inhibition of the Na⁺,K⁺,2Cl^- symporter. Investigations of the Li⁺ efflux via the Na⁺/Li⁺ exchanger using atom absorption spectroscopy revealed that aldosterone has no effect on this transporter. Studies of the effect of aldosterone on the Ca²⁺ content and the intracellular pH (pH_i) were carried out on single RBCs with a fluorescence imaging system. Both parameters are affected by aldosterone. The Ca²⁺ uptake in the presence of aldosterone, under conditions where the Ca²⁺ pump is inhibited, showed marked differences from the control. Since the effect is nifedipine-sensitive, it seems that aldosterone affects a Ca²⁺ channel. In addition, aldosterone leads to an acidification of the intracellular medium after an initial alkalisation due to an effect on the Na⁺/H⁺ exchanger.