Incubation of OKP cells in low-K+ media increases NHE3 activity after early decrease in intracellular pH

Chronic hypokalemia increases the activity of proximal tubule apical membra ne Na+/H+ antiporter NHE3. The present study examined the effect of the inc ubation of OKP cells tan opossum kidney, clone P cell line) in control medi um {K+ concn ([K+]) = 5.4 mM} or low-K+ medium ([K+] = 2.7 mM) on NHE3. The activity of an ethylisopropyl amiloride-resistant Na+/H+ antiporter, whose characteristics were consistent with those of NHE3, was increased in low-K + cells beginning at 8 h. NHE3 mRNA and NHE3 protein abundance were increas ed 2.2-fold and 62%, respectively, at 24 h but not at 8 h. After incubation in low-K+ medium, intracellular pH (pH(i)) decreased by 0.27 pH units (max imum at 27 min) and then recovered to the control level. Intracellular acid osis induced by 5 mM sodium propionate increased Na+/H+ antiporter activity at 8 and 24 h. Herbimycin A, a tyrosine kinase inhibitor, blocked low-K+- and sodium propionate-induced activation of the Na+/H+ antiporter at 8 and 24 h. Our results demonstrate that low-K+ medium causes an early decrease i n pH(i), which leads to an increase in NKE3 activity via a tyrosine kinase pathway.