Effects of pH on adrenal angiotensin receptors and responses

Ambient hydrogen ion concentration modulates the effects of angiotensin II (AII) on adrenal aldosterone secretion, but the mechanism of this modulation is unknown. We examined the influence of pH on AII receptors and responses in bovine adrenal glomerulosa cells. Lowering pH from 7.4 to 6.8 increased AII binding 20.5% and increased maximal All-stimulated aldosterone secretion 43%. By contrast, at pH 8.0, All binding and stimulation of aldosteronogenesis fell by 56.6% and 39%, respectively. Effects on All binding intermediate to these changes were observed at pH 7.1 and 7.7. Similar effects of altered pH were observed on All binding to a crude membrane fraction of bovine glomerulosa cells. Analysis indicated that pH primarily affected receptor number rather than affinity. In studies of proposed postreceptor mediators of All actions, pH had no effect on All stimulation of phosphatidylinositol turnover or All inhibition of calcium influx. The results show that pH affects All interaction with its receptors. The larger magnitude of the change in aldosterone compared with receptor binding suggests that a postreceptor step is also altered by pH; however, this postreceptor step is not reflected in calcium influx or phospholipid turnover.