Role of JNK in hypertonic activation of Cl--dependent Na+/H+ exchange in Xenopus oocytes

1 Department of Biological Science, University of Alberta, Edmonton, Alberta, Canada T6G 2E9, 2 Molecular Medicine and Renal Units, Beth Israel Deaconess Medical Center, Boston; and Departments of 3 Medicine and 4 Cell Biology, Harvard Medical School, Boston, Massachusetts 02215 In the course of studying the hypertonicity-activated ion transporters in Xenopus oocytes, we found that activation of endogenous oocyte Na + /H + exchange activity (xoNHE) by hypertonic shrinkage required Cl , with an EC 50 for bath [Cl ] of ~3 mM. This requirement for chloride was not supported by several nonhalide anions and was not shared by xoNHE activated by acid loading. Hypertonicity-activated xoNHE exhibited an unusual rank order of inhibitory potency among amiloride derivatives and was blocked by Cl transport inhibitors. Chelation of intracellular Ca 2+ by injection of EGTA blocked hypertonic activation of xoNHE, although many inhibitors of Ca 2+ -related signaling pathways were without inhibitory effect. Hypertonicity activated oocyte extracellular signal-regulated kinase 1/2 (ERK1/2), but inhibitors of neither ERK1/2 nor p38 prevented hypertonic activation of xoNHE. However, hypertonicity also stimulated a Cl -dependent increase in c-Jun NH 2 -terminal kinase (JNK) activity. Inhibition of JNK activity prevented hypertonic activation of xoNHE but not activation by acid loading. We conclude that hypertonic activation of Na + /H + exchange in Xenopus oocytes requires Cl and is mediated by activation of JNK. Na + /H + exchange; c-Jun NH 2 -terminal kinase; extracellular signal-regulated kinase; p38; transport; SP600125; U-0126