MINERALOCORTICOID RECEPTORS AND 11-BETA-STEROID DEHYDROGENASE-ACTIVITY IN RENAL PRINCIPAL AND INTERCALATED CELLS

Aldosterone exerts complex effects on the cortical collecting duct (CCD): it increases Na+ and K+ transport, and it also influences H+ and HCO3 transport. Whether these latter effects represent direct action of aldosterone on intercalated cells (ICC) or are secondary to changes in the transport of other electrolytes is unclear. Because the presence of specific receptors is the prerequisite of a direct steroid action, and mineralocorticoid receptors (MR) have not yet been demonstrated in ICC, in this study we determined the density of MR directly in isolated principal cells (PC) and beta-ICC. Purified populations of these two cell types were obtained from rabbit renal cortex by immunodissection and fluorescence-activated cell sorting. We found that both PC and beta-ICC contained a significant number of MR, although receptor density was higher in PC than in beta-ICC (6,704 +/- 912 vs. 2,181 +/- 388 MR sites/cell; P < 0.001). 11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD), an enzyme that is present predominantly in mineralocorticoid target cells, exhibited a distribution similar to that of MR in the two cell types. 11 beta-OHSD activity, determined by measuring the rate of conversion of [H-3]corticosterone to 11-dehydrocorticosterone, was 1.08 + 0.14 and 0.34 +/- 0.08 fmol.min(-1) 1,000 cells(-1) (P < 0.001) in intact PC and P-ICC, respectively. 11 beta-OHSD in both cell types utilized NAD as cofactor. These results suggest that beta-ICC are potential direct targets of aldosterone and that MR in both PC and beta-ICC are protected by 11 beta-OHSD.