a4, a Unique Kidney-specific Isoform of Mouse Vacuolar H+-ATPase Subunit a

The vacuolar-type H+-ATPase (V-ATPase) translocates protons across membranes. Here, we have identified a mouse cDNA coding for a fourth isoform (a4) of the membrane sector subunit a of V-ATPase. This isoform was specifically expressed in kidney, but not in the heart, brain, spleen, lung, liver, muscle, or testis. Immunoprecipitation experiments, together with sequence similarities for other isoforms (a1, a2, anda3), indicate that the a4 isoform is a component of V-ATPase. Moreover, histochemical studies show thata4 is localized in the apical and basolateral plasma membranes of cortical α- and β-intercalated cells, respectively. These results suggest that the V-ATPase, with the a4 isoform, is important for renal acid/base homeostasis.