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 membrane Na(+)/H(+) antiporter NHE3. The present study examined the effect of the incubation of OKP cells tan opossum kidney, clone P cell line) in control medium {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 increased 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 (maximum at 27 min) and then recovered to the control level. Intracellular acidosis 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 in pH(i), which leads to an increase in NKE3 activity via a tyrosine kinase pathway.