Functional activity of h-k-atpase in individual cells of the outer
medullary collecting duct: localization and effect of k+
depletion.
Kuwahara, Michio, Wei-Jie Fu, and Fumiaki Marumo.
Second Department of Internal Medicine, Tokyo Medical and Dental
University, Tokyo 113, Japan
APStracts 2:0137F, 1995.
Recent studies have indicated the presence of 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 x10-3 pHU/s in intercalated cells 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 SCH28080 (10 [mu]M), 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.
Received 23 January 1995; accepted in final form 12 July 1995.
APS Manuscript Number F18-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.