Cross-talk between the Na(+)-K(+)-ATPase and the H(+)-ATPase in proximal tubules in suspension.

The cellular energy required for the activity of the Na(+)-K(+)-ATPase and of the H(+)-ATPase was estimated in intact proximal tubules in suspension. Both the fall in oxygen consumption (directly measured) and NADH oxidation (as estimated from exogenous substrate metabolism) were measured before and following application of ouabain (1 mM) to inhibit the sodium pump, following bafilomycin (0.1 mM) to inhibit the proton pump or following a combination of these inhibitors. The data demonstrate that the sodium pump utilizes 43% and the proton pump 19% of the phosphorylating NADH turnover of canine proximal tubules studied in vitro. However, a significant and stoichiometric stimulation of one pump was observed upon inhibition of the other. The NADH turnover related to the sodium pump increased from 308 to 402 (delta = 94) mumol.g-1 wet weight.h-1 following bafilomycin application and that of the proton pump from 136 to 230 (delta = 94) following ouabain application. This stimulation was largely abolished by inhibition of the Na+/H+ exchange occurring in either direction by amiloride or methylisobutylamiloride. It is concluded that a cross-talk occurs between the basolateral sodium pumps and the proton pumps located on the brush border membrane and/or on endosomes in proximal tubules. This cross-talk appears to be mediated by Na+/H+ exchange suggesting that both the proton pump and the Na+/H+ exchanger may contribute in a cooperative fashion to the proximal secretion of protons.