Na+-H+ and Na+-Ca2+ exchange in glomerulosa cells: possible role in control of aldosterone production.

Sodium uptake by rat adrenal glomerulosa cells was stimulated by intracellular acidosis evoked by Na+-propionate. This process was inhibited by 5-(N,N-hexamethylene) amiloride (HMA), a known inhibitor of the Na+-H+ exchange. These experiments demonstrate the existence of the Na+-H+ exchange in glomerulosa cells. Although amiloride inhibited the angiotensin II- and adrenocorticotropic hormone (ACTH)-induced aldosterone response, HMA, a more specific inhibitor of Na+-H+ exchange, failed to do that. 45Ca2+ influx and efflux were dependent on intra- and extracellular Na+ concentrations. Amiloride analogues, known to inhibit Na+-Ca2+ exchange, reduced basal 45Ca influx. Although we could not reveal the activation of Na+-Ca2+ exchange by angiotensin II, inhibitors of Na+-Ca2+ exchange also inhibited the angiotensin- and ACTH-induced aldosterone response of glomerulosa cells. Our results suggest that Na+-Ca2+ exchange supports the maintenance of basal Ca2+ level in the cytoplasma of glomerulosa cells, and amiloride derivatives inhibit aldosterone production by reducing Ca2+ level below resting values.