H+-K+-ATPASE ACTIVITY IN RAT COLLECTING DUCT SEGMENTS

Previous studies have suggested the presence of an H+-K+-ATPase in rat cortical and medullary intercalated cells with similar properties to the gastric proton pump. The purpose of this study was to determine the functional contribution of an H+-K+-adenosinetriphosphatase(ATPase) to total CO2 (tCO2) transport along the rat collecting duct. After baseline determination of tCO2 transport in isolated perfused collecting duct segments, Sch 28080 (10-mu-M) was added to either the perfusate or bath. When Sch 28080 was added to the perfusate, there was no effect in the cortical collecting duct (CCD, 20.8 +/- 6.7 vs. 25.3 + 3.0 pmol.mm-1.min-1), but a marked decrease in tCO2 absorption was effected in both the outer medullary (OMCD, 37.6 + 6.2 vs. 10.7 +/- 4.1 pmol.mm-1.min-1) and initial inner medullary collecting duct (IMCD1, 34.4 +/- 8.1 vs. 16.2 +/- 5.6 pmol.mm-1.min-1). In the CCD from rats with acute alkalosis in vivo, Sch 28080 added to the bath inhibited tCO2 secretion in the CCD (-17.1 +/- 4.4 vs 3.5 + 3.3 pmol.mm-1.min-1). These findings suggest that 1) H+-K+-ATPase is important in tCO2 absorption in the OMCD and IMCD1 and in tCO2 secretion in the CCD, 2) HCO3--absorbing intercalated cells differ functionally in the cortex and medulla, 3) HCO3- secretion is not the reverse process of HCO3- absorption in the CCD, and 4) H+-K+-ATPase is important in distal acidification under normal and altered acid-base conditions.