Conlin P R, Cirillo M, Zerbini G, Williams G H, Canessa M L
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Endocrinology. 1993 Mar;132(3):1345-52. doi: 10.1210/endo.132.3.8382599.
Intracellular pH (pHi) regulation by Na(+)-H+ exchange is important in cellular responses to hormones and growth factors, particularly those which raise cytosolic Ca2+ (Cai). Since elevation of Cai occurs when adrenal glomerulosa cells are stimulated by angiotensin II (Ang II) and high external K+ (Ko), we evaluated the relationship of Na(+)-H+ exchange to calcium movement particularly during high Ko stimulation of bovine glomerulosa cells. Inhibition of Na(+)-H+ exchange by dimethylamiloride markedly reduced aldosterone secretion in response to 8 mM Ko. This high Ko stimulation was accompanied by a rise in dimethylamiloride-sensitive Na+ influx and pHi acidification which was extracellular Ca2+ (Cao) dependent. High Ko also produced a rise in Ca2+ influx, Cai 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 pHi which was independent of Cao. After PKC depletion by phorbol ester pretreatment, Ang II also produced a Cao-dependent cell acidification as with high Ko. Thus, Na(+)-H+ exchange is activated by both Ang II and high Ko but by different mechanisms. High Ko 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 Ko and Ang II stimulation of aldosterone secretion.
通过钠氢交换调节细胞内pH值（pHi）在细胞对激素和生长因子的反应中很重要，特别是那些能提高胞质Ca2+（Cai）的反应。由于当肾上腺球状带细胞受到血管紧张素II（Ang II）和高细胞外钾（Ko）刺激时会出现Cai升高，我们评估了钠氢交换与钙移动的关系，特别是在高Ko刺激牛球状带细胞期间。二甲基amiloride对钠氢交换的抑制显著降低了对8 mM Ko的醛固酮分泌反应。这种高Ko刺激伴随着二甲基amiloride敏感的Na+内流增加和pHi酸化，且依赖于细胞外Ca2+（Cao）。高Ko在37℃时还使Ca2+内流、Cai水平和Ca2+外流增加。然而，在4℃时，Ca2+内流保持完整，但Ca2+外流和细胞酸化受到抑制。相反，Ang II导致蛋白激酶C（PKC）激活，同时pHi依赖于钠氢交换而升高，且与Cao无关。在用佛波酯预处理耗尽PKC后，Ang II也像高Ko一样导致依赖于Cao的细胞酸化。因此，钠氢交换被Ang II和高Ko激活，但机制不同。高Ko刺激诱导细胞酸化增强，而Ang II诱导由反向转运体的PKC激活驱动的碱化。这些发现表明，钠氢交换的生理作用可能部分是抵消在高Ko和Ang II刺激醛固酮分泌期间因增强的主动Ca2+外流（通过Ca2+泵出）而产生的酸化。
