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

1 North Florida/South Georgia Veterans Health System and 2 College of Medicine, University of Florida, Gainesville, Florida; and 3 College of Medicine, University of Cincinnati, Cincinnati, Ohio Submitted 5 September 2007 ; accepted in final form 5 December 2007 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 -subunits are expressed in the CD: HK 1 and HK 2 . Both exhibit K dependence but have different inhibitor sensitivities. The HK 1 H-K-ATPase is Sch-28080 sensitive, whereas the pharmacological profile of the HK 2 H-K-ATPase is not completely understood. The present study used a nonpharmacological, genetic approach to determine the contribution of HK 1 and HK 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 1 , HK 2 , or both H-K-ATPases (HK 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 µM), respectively. Here, we report 1 ) initial pH i and buffering capacity were not significantly altered in the ICs of HK -deficient mice, 2 ) either HK 1 or HK 2 deficiency resulted in slower acid extrusion, and 3 ) A-type ICs from HK 1,2 -deficient mice had significantly slower acid extrusion compared with A-type ICs from HK 1 -deficient mice alone. These studies are the first nonpharmacological demonstration that both HK 1 and HK 2 contribute to H secretion in both A-type and B-type ICs in animals fed a normal diet. potassium; microperfusion; pH; acid-base balance; P-type ATPase Address for reprint requests and other correspondence: I. Jeanette Lynch, Malcom Randall VA Medical Center, General Medical Research Service, 1601 SW Archer Rd., Gainesville, FL 32608 (e-mail: lynchj{at}ufl.edu )