Heterogeneity of H-K-ATPase-mediated acid secretion along the mouse collecting duct

Abstract

In the collecting duct (CD), H-K-ATPases function in cation reabsorption and H secretion. This study evaluated H-K-ATPase-mediated H secretion along the mouse CD, measured as EIPA- and luminal bafilomycin A1-insensitive intracellular pH (pHi) recovery from acute H loading (NH4) using BCECF. pHirecovery was measured in 1) microperfused cortical, outer medullary, and inner medullary CDs (CCD, OMCD, and IMCD) from C57BL/6J mice fed a normal diet and 2) common murine CD cell lines. H-K-ATPase activity along the native, microperfused CD was greatest in the CCD, less in the OMCD, and least in the IMCD (0.10 ± 0.02, 0.04 ± 0.01, and 0.01 ± 0.002 U/min, respectively). H-K-ATPase activity was 0.30 ± 0.03 and 0.26 ± 0.03 in A- and B-type ICs, respectively, and was sensitive to Sch-28080 or ouabain. pHirecovery was greatest in the OMCD1cell line (0.25 ± 0.01) and less in mpkCCDc14(0.17 ± 0.01), mIMCD-K2 (0.12 ± 0.01), and mIMCD-3 (0.05 ± 0.01) cells. EIPA inhibited the majority of pHirecovery in these cells (100%, 64%, 75%, and 80% in mpkCCDc14, OMCD1, mIMCD-K2, and mIMCD-3, respectively). In OMCD1cells, where EIPA-insensitive pHirecovery was greatest, H-K-ATPase activity was 0.10 ± 0.01 and was significantly inhibited (80%) by Sch-28080. We conclude that 1) H-K-ATPase-mediated H secretion in the native mouse CD is greatest in the ICs of the CCD, 2) A- and B-type ICs possess HKα1and HKα2H-K-ATPase activity, and 3) the OMCD1cell line best exhibits H-K-ATPase.