alpha 4, a unique kidney-specific isoform of mouse vacuolar H+-ATPase subunit a

The vacuolar-type H+-ATPase (V-ATPase) translocates protons across membrane s. Here, we have identified a mouse cDNA coding for a fourth isoform (a4) o f the membrane sector subunit a of V-ATPase. This isoform was specifically expressed in kidney, but not in the heart, brain, spleen, lung, liver, musc le, or testis. Immunoprecipitation experiments, together with sequence simi larities for other isoforms (a1, a2, and a3), indicate that the a4 isoform is a component of V-ATPase. Moreover, histochemical studies show that a4 is localized in the apical and basolateral plasma membranes of cortical alpha - and beta -intercalated cells, respectively. These results suggest that th e V-ATPase, with the a4 isoform, is important for renal acid/base homeostas is.