Analysis of H,K‐ATPase‐mediated acid secretion along the mouse collecting duct

Abstract

In the collecting duct (CD), the H,K‐ATPases function in cation reabsorption and H secretion. The purpose of this study was to evaluate H,K‐ATPase‐mediated H secretion along the CD. Intracellular pH (pHi) recovery to acute H loading was investigated in 1) common CD cell lines and 2) in the microperfused cortical, outer medullary, and inner medullary CD (CCD, OMCD, IMCD). pHi recovery rates (U/min) were greatest in the OMCD1 cell line (0.25 ± 0.01), followed by mpk‐CCDc14 (0.17 ± 0.01), mIMCD‐K2 (0.12 ± 0.01), and mIMCD‐3 (0.06 ± 0.02) cells. Na,H‐exchange inhibition (EIPA) diminished the majority of pHi recovery in these cells (65%, 97%, 74%, and 90%, respectively). In OMCD1, where EIPA‐insensitive pHi recovery was greatest, H,K‐ATPase activity was 0.10 ± 0.01 measured as EIPA‐ and bafilomycin A1 (H‐ATPase inhibitor)‐insensitive (EBI) pHi recovery. Sch28080 (HKa1 inhibitor) significantly inhibited this recovery by 84%. EBI pHi recovery was greatest in the microperfused CCD (0.10 ± 0.02) then in OMCD (0.04 ±0.01) and was minimal in IMCD (0.01 ± 0.00). EBI pHi recovery was 0.30 ± 0.03 and 0.26 ± 0.03 in A‐ and B‐type ICs and was Sch28080 or ouabain (HKα2 inhibitor) sensitive. These data suggest: 1) H,K‐ATPase mediated H secretion is greatest in the CCD, 2) both A‐ and B‐type ICs possess HKα1 and HKα2 H,K‐ATPase isoforms, and 3) the OMCD1 cell line best exhibits H,K‐ATPase activity. This work was funded by NIH Grant R01‐DK‐049750.