Our previous studies with intact dogs and with a isolated perfused adrenal gland preparation has provided strong evidence suggesting that osmolality and pH play an important role in modulating the response of the glomerulosa cells to AII, ACTH and elevations in potassium concentration. Small changes in osmolality were shown to have a powerful inverse effect on AII- and (K)- but not on ACTH- stimulated aldosterone secretion. More recently, we have shown that changes in (H+) act directly on the adrenal gland to modulate AII-, (K)- and ACTH-stimulated aldosterone secretion. These findings may help to explain many of the physiological and pathophysiological situations in which plasma aldosterone concentration does not correlate with the plasma concentration of AII or (K) such as water deprivation, hypertension, congestive heart failure, primary aldosteronism, hepatic cirrhosis, acid/base disturbances and exposure to high altitudes. However, little is known about the cellular mechanisms involved in mediating the effects of osmolality or the (H+) ion on aldosterone secretion. Our preliminary studies with a recently developed primary culture of collagenase-dispersed bovine glomerulosa cell preparation indicate that changes in osmolality interfere with AlI-induced increases in (Ca2+)i suggesting that osmolality may alter AII and (K) but not ACTH induced aldosterone secretion by altering calcium metabolism of the glomerulosa cells either directly or indirectly by altering either the volume of the glomerulosa cells or the flux of the Na' K' Cl or (H) ion. We now propose to investigate the mechanism underlining osmotic and pH modulation of hormone induced aldosterone secretion in terms of the effect that alterations In osmolality and pH have 1) on glomerulosa cell volume isotope dilution principle), 2) on (Ca2+)i (fura-2 fluoremetery) and the cellular processes involved in determining (Ca2+)i (Ca45 efflux and influx) and 3) on the transmembrane fluxes of Na, K, Cl and (H) ions (radioisotope uptake and efflux). For all our studies the recently developed preparation of primary cultured bovine glomerulosa cells will be used.
