Impaired acid secretion in cortical collecting duct intercalated cells from H-K-ATPase-deficient mice:: role of HKα isoforms

Two classes of H pumps, H-K-ATPase and H-ATPase, contribute to luminal acidification and HCO(3) transport in the collecting duct (CD). At least two H-K-ATPase alpha-subunits are expressed in the CD: HK alpha(1) and HK alpha(2). Both exhibit K dependence but have different inhibitor sensitivities. The HK alpha(1) H-K-ATPase is Sch-28080 sensitive, whereas the pharmacological profile of the HK alpha(2) H-K-ATPase is not completely understood. The present study used a nonpharmacological, genetic approach to determine the contribution of HK alpha(1) and HK alpha(2) to cortical CD (CCD) intercalated cell (IC) proton transport in mice fed a normal diet. Intracellular pH (pH(i)) recovery was determined in ICs using in vitro microperfusion of CCD after an acute intracellular acid load in wild-type mice and mice of the same strain lacking expression of HK alpha(1), HK alpha(2), or both H-K-ATPases (HK alpha(1,2)). A-type and B-type ICs were differentiated by luminal loading with BCECF-AM and peritubular chloride removal from CO(2)/HCO(3)-buffered solutions to identify the membrane locations of Cl/HCO(3) exchange activity. H-ATPase- and Na/H exchange-mediated H transport were inhibited with bafilomycin A(1) 100 nM) and EIPA (10 mu M), respectively. Here, we report 1) initial pHi and buffering capacity were not significantly altered in the ICs of HK alpha-deficient mice, 2) either HK alpha(1) or HK alpha(2) deficiency resulted in slower acid extrusion, and 3) A-type ICs from HK alpha(1,2)-deficient mice had significantly slower acid extrusion compared with A-type ICs from HK alpha(1)-deficient mice alone. These studies are the first nonpharmacological demonstration that both HK alpha(1) and HK alpha(2) contribute to H secretion in both A-type and B-type ICs in animals fed a normal diet.