EFFECTS OF CORTICOSTEROIDS ON PARAMETERS RELATED TO NA+ TRANSPORT BY AMPHIBIAN RENAL DISTAL CELLS (A6) IN CULTURE

The present study addresses the effects of the hormones aldosterone an d corticosterone, as well as those of dexamethasone, on cultured renal amphibian cells, focusing on parameters thought relevant for the furt her understanding of the regulation by these steroids of Na+ reabsorpt ion along the renal tubule. Exposure to these steroids of A6 cell mono layers grown on a permeable support produced a motor, dose-dependent, increase in Na+ transport, reflected by the short-circuit current, I-s c, (Na+ + K+)-ATPase activity and ouabain binding, both of which are l inearly correlated with I-sc in control tissue, also increased signifi cantly after steroid treatment. Dexamethasone was consistently more ac tive than corticosterone and aldosterone on the parameters studied. Th e increase in I-sc and (Na+ + K+)-ATPase activity elicited by dexameth asone could be blocked by the glucocorticoid antagonist RU 486, wherea s it was only slightly reduced by the mineralocorticoid antagonist, sp ironolactone. In contrast, the latter strikingly reduced the effects o f aldosterone on these parameters, unlike RU 486. Furthermore, the eff ects of large doses of dexamethasone and aldosterone combined were not additive. Taken together, the data presented appear compatible with t he view that the effects of aldosterone on Na+ transport by A6 cells a re mediated by a fraction of the receptors involved in the response to dexamethasone; they furthermore raise the question of whether, in low er vertebrates, it is relevant to make a distinction between ''gluco'' and ''mineralo''corticoids. Copyright (C) 1996 Elsevier Science Ltd.