Functional identification of H-K-ATPase in intercalated cells of cortical collecting tubule.

A K-dependent proton extrusion mechanism was investigated by means of fluorescence techniques in rabbit cortical collecting tubules. These experiments were performed in split opened tubules from normal animals exposed to the intracellular pH (pH(i)) indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. This preparation permitted the separate study of the intercalated cells (IC) from the principal cells (PC). In IC pH(i) recovery in response to an acute acid load was observed under Na-free conditions on addition of 5 mM K. This K-dependent recovery of pH(i) in the IC was only partial, but was Sch 28080 inhibitable (10(-5) M) and ouabain insensitive. This suggests the process is mediated by an H-K-adenosinetriphosphatase similar to that of gastric cells. The PC were capable of recovering from the acid load, but this Na-independent response was not blocked by the Sch 28080, suggesting some other mechanism for this result. In both cell types reintroduction of Na into the superfusate resulted in full recovery back to the initial pH(i), presumably the result of Na/H exchange.