Calcium-mediated intracellular acidification and activation of Na+-H+ exchange in adrenal glomerulosa cells stimulated with potassium

Intracellular pH (pHi) regulation by Na⁺-H⁺ exchange is important in cellular responses to hormones and growth factors, particularly those which raise cytosolic Ca²⁺ (Ca_i). Since elevation of Ca_i occurs when adrenal glomerulosa cells are stimulated by angiotensin II (Ang II) and high external K⁺ (K_o), we evaluated the relationship of Na⁺-H⁺ exchange to calcium movement particularly during high K_o stimulation of bovine glomerulosa cells. Inhibition of Na⁺-H⁺ exchange by dimethylamiloride markedly reduced aldosterone secretion in response to 8 mM K_o. This high K_o stimulation was accompanied by a rise in dimethylamiloride-sensitive Na⁺ influx and pHi acidification which was extracellular Ca²⁺ (Ca_o) dependent. High K_o also produced a rise in Ca²⁺ influx, Ca_i levels and Ca²⁺ efflux at 37 C. However, at 4 C, Ca²⁺ influx remained intact, but Ca²⁺ efflux and cellular acidification were inhibited. In contrast, Ang II produced protein kinase C (PKC) activation accompanied by a Na⁺-H⁺ exchange-dependent rise in pH_i which was independent of Ca_o. After PKC depletion by phorbol ester pretreatment, Ang II also produced a Ca_o-dependent cell acidification as with high K_o. Thus, Na⁺-H⁺ exchange is activated by both Ang II and high K_o but by different mechanisms. High K_o stimulation induces an enhanced cellular acidification, whereas Ang II induces alkalinization driven by PKC activation of the antiporter. These findings suggest that a physiological role of Na⁺-H⁺ exchange may be, in part, to counteract the acidification produced by enhanced active Ca²⁺ efflux (via Ca²⁺ pumping) during both high K^o and Ang II stimulation of aldosterone secretion.