Adaptation to low-K+ media increases H(+)-K(+)-ATPase but not H(+)-ATPase-mediated pHi recovery in OMCD1 cells.
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.
Guntupalli
J
J
Department of Internal Medicine, University of Texas Medical School, Houston 77030, USA.
Onuigbo
M
M
Wall
S
S
Alpern
R J
RJ
DuBose
T D
TD
D000222:Adaptation, Physiological; D000818:Animals; D002460:Cell Line; D003470:Culture Media / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase / Q000502:physiology*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D011188:Potassium / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000502:physiology*; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000502:physiology
D003470:Culture Media; D006859:Hydrogen; D012964:Sodium; D017506:H(+)-K(+)-Exchanging ATPase; D006180:Proton-Translocating ATPases; D012413:Rubidium; D011188:Potassium