title: Functional activity of H-K-ATPase in individual cells of OMCD: localization and effect of K+ depletion.
abstract: Recent studies have indicated the presence of hydrogen-potassium-adenosinetriphosphatase (H-K-ATPase) in the collecting duct. We examined the localization of functional H-K-ATPase activity in individual cells of the outer and inner stripes of outer medullary collecting ducts (OMCDo and OMCDi). Tubules were isolated from control and K(+)-depleted rabbits and perfused in vitro. Intracellular pH (pHi) of principal cells, intercalated cells, and OMCDi cells was monitored by fluorescence ratio imaging using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). An intracellular acid load was induced by NH3/NH4 prepulse in extracellular Na(+)-, K(+)-, and HCO3(-)-free condition, and then 5 mM K+ was added to the lumen or the bath in the presence of Ba2+. Functional activity of H-K-ATPase was estimated by the difference in the rates of pHi recovery before and after K+ addition. In the control condition, luminal addition of K+ significantly increased the pHi recovery rate by 1.6 +/- 0.4 and 1.9 +/- 0.4 x 10(-3) pH units/s in intercalated calls and OMCDi cells, respectively, but not in principal cells. This K(+)-dependent pHi recovery was inhibited by 63% in intercalated cells and 74% in OMCDi cells in the presence of luminal Sch-28080 (10 microM) but was not affected in the presence of luminal bafilomycin-A1 (10 nM). K+ depletion increased the K(+)-dependent pHi recovery to 2.3-fold in intercalated cells and 2.6-fold in OMCDi cells. By contrast, K(+)-dependent pHi recovery was not detected in the basolateral membrane of any cell types in either the control or the K(+)-depleted condition. These results provide functional evidence that H-K-ATPase is distributed in the luminal membrane of intercalated cells and OMCDi cells and that this ATPase is activated by K+ depletion, suggesting the contribution of intercalated cells and OMCDi cells to K+ conservation in rabbit OMCD.
authors.affiliation: Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kuwahara
authors.forename: W J
authors.initials: WJ
authors.lastname: Fu
authors.forename: F
authors.initials: F
authors.lastname: Marumo
mesh_terms: D000818:Animals; D005260:Female; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011191:Potassium Deficiency / Q000378:metabolism*; D011817:Rabbits; D014018:Tissue Distribution
chemical_list: D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium