ACELL Mar. 45/3

Amemiya, Morimasa, Kaoru Tabei, Eiji Kusano, Yasushi Asano, and Robert J. Alpern. Incubation of OKP cells in low-K1 media increases NHE3 activity after early decrease in intracellular pH. Am. J. Physiol. 276 (Cell Physiol. 45): C711–C716, 1999.—Chronic hypokalemia increases the activity of proximal tubule apical membrane Na1/H1 antiporter NHE3. The present study examined the effect of the incubation of OKP cells (an opossum kidney, clone P cell line) in control medium 5K1 concn ([K1]) 5 5.4 mM6 or low-K1 medium ([K1] 5 2.7 mM) on NHE3. The activity of an ethylisopropyl amiloride-resistant Na1/H1 antiporter, whose characteristics were consistent with those of NHE3, was increased in low-K1 cells beginning at 8 h. NHE3 mRNA and NHE3 protein abundance were increased 2.2-fold and 62%, respectively, at 24 h but not at 8 h. After incubation in low-K1 medium, intracellular pH (pHi) decreased by 0.27 pH units (maximum at 27 min) and then recovered to the control level. Intracellular acidosis induced by 5 mM sodium propionate increased Na1/H1 antiporter activity at 8 and 24 h. Herbimycin A, a tyrosine kinase inhibitor, blocked low-K1and sodium propionate-induced activation of the Na1/H1 antiporter at 8 and 24 h. Our results demonstrate that low-K1 medium causes an early decrease in pHi, which leads to an increase in NHE3 activity via a tyrosine kinase pathway.