AJP - Cell Physiology, Vol 273, Issue 2 C558-C571, Copyright © 1997 by American Physiological Society

ARTICLES

Adaptation to low-K+ media increases H(+)-K(+)-ATPase but not H(+)-ATPase-mediated pHi recovery in OMCD1 cells

J. Guntupalli, M. Onuigbo, S. Wall, R. J. Alpern and T. D. DuBose Jr
Department of Internal Medicine, University of Texas Medical School, Houston 77030, USA.

Studies in rat and rabbit outer medullary collecting duct of inner stripe origin (OMCDis) suggest that both H(+)-ATPase and H(+)-K(+)-ATPase participate in H+ secretion. However, the relative contributions of these transporters, and, in particular, that of H(+)-K(+)-ATPase to K+ absorption have not been defined precisely. The present study was designed to delineate more clearly the response of these two transporters to hypokalemia and acidosis in a newly developed mouse OMCD1 cell line. In cells grown in normal K+ (5 mM) media, intracellular pH (pHi) recovery was similar either in the presence or absence of K+ in the perfusate (delta pHi/min = 0.014 +/- 0.001 vs. 0.017 +/- 0.003, not significant). The inhibitory effects of Sch-28080 (10 microM) and bafilomycin A1 (10 nM) on pHi recovery were evident only in the presence and absence of K+ in the perfusate, respectively. In cells grown in low-K+ (2.5 mM) media to simulate chronic hypokalemia, pHi recovery was significantly faster than in cells grown in normal K+ media (delta pHi/min = 0.045 +/- 0.01 vs. 0.014 +/- 0.001, P < 0.01) and was inhibited specifically by Sch-28080, not by bafilomycin A1. In contrast, in cells preconditioned to low pH (7.0) to simulate chronic acidosis, the enhanced pHi recovery was abolished by bafilomycin A1 but not by Sch-28080. 86Rb+ uptake, when used as a K+ congener, was inhibited by Sch-28080. The K(m) for 86Rb+ uptake (H(+)-K(+)-ATPase activity) and the 50% inhibitory concentration for Sch-28080 were 270 and 5.0 microM, respectively. These studies provide evidence that, in morphologically homogeneous OMCD1 cells, 1) both H(+)-K(+)-ATPase and H(+)-ATPase participate in pHi regulation, 2) the H(+)-K(+)-ATPase is selectively upregulated by preconditioning in low-K+ media, and 3) conversely, preconditioning in low-pH media stimulates only the H(+)-ATPase. Thus, in OMCDis, the H(+)-K(+)-ATPase and H(+)-ATPase respond selectively and independently to chronic hypokalemia and acidosis, respectively.

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