Luminal acidification in K-replete OMCDi: contributions of H-K-ATPase and bafilomycin-A1-sensitive H-ATPase.

We have previously demonstrated that basolateral addition of the gastric H-K-adenosinetriphosphatase (H-K-ATPase) inhibitor Sch-28080 (10 microM) profoundly reduced net total CO2 flux (JtCO2) in the inner stripe of the outer medullary collecting duct (OMCDi) of K-replete rabbits. In the present studies, we first addressed whether the inhibitory effect of Sch-28080 is dependent on the side of the membrane to which it is added. Second, we reassessed the relative magnitude of contribution of H-K-ATPase. Third, we formally tested whether a bafilomycin-A1 (BAF)-sensitive H-ATPase also contributes to luminal acidification in the OMCDi under K-replete dietary conditions. We found that luminal addition of the structurally and functionally dissimilar gastric H-K-ATPase inhibitor A80915A (10 microM) profoundly reduced JtCO2 while transepithelial voltage (VT) was unchanged. This degree of inhibition was statistically indistinguishable from our previous results when Sch-28080 was applied basolaterally. Inhibition of JtCO2 by the less membrane-permeable N-methyl cation of Sch-28080, H224/25, was significant when applied luminally but was not significant when applied basolaterally. VT was not significantly affected by either the luminal or basolateral addition of H224/25. To evaluate the possible contribution of an H-ATPase, the effect of both 5.0 nM and 10.0 nM luminal BAF on JtCO2 and VT was examined. At 5.0 nM, BAF significantly inhibited JtCO2). However, this observation was significantly less (P < 0.05) than the inhibition observed with 10 microM A80915A. No additional inhibition was observed by increasing the concentration of BAF to 10.0 nM.(ABSTRACT TRUNCATED AT 250 WORDS)