Distinct expression patterns of different subunit Isoforms of the V-ATPase in the rat epididymis

In the epididymis and vas deferens, the vacuolar H(+)ATPase (V-ATPase), located in the apical pole of narrow and clear cells, is required to establish an acidic luminal pH. Low pH is important for the maturation of sperm and their storage in a quiescent state. The V-ATPase also participates in the acidification of intracellular organelles. The V-ATPase contains many subunits, and several of these subunits have multiple isoforms. So far, only subunits ATP6V1B1, ATP6V1B2, and ATP6V1E2, previously identified as 131, 132, and E subunits, have been described in the rat epididymis. Here, we report the localization of V-ATPase subunit isoforms ATP6V1A, ATP6V1C1, ATP6V1C2, ATP6V1G1, ATP6V1G3, ATP6V0A1, ATP6V0A2, ATP6V0A4, ATP6V0D1, and ATP6V0D2, previously labeled A, C1, C2, G1, G3, a1, a2, a4, d1, and d2, in epithelial cells of the rat epididymis and vas deferens. Narrow and clear cells showed a strong apical staining for all subunits, except the ATP6V0A2 isoform. Subunits ATP6V0A2 and ATP6V1A were detected in intracellular structures closely associated but not identical to the TGN of principal cells and narrow/clear cells, and subunit ATP6V0D1 was strongly expressed in the apical membrane of principal cells in the apparent absence of other V-ATPase subunits. In conclusion, more than one isoform of subunits ATP6V1C, ATP6V1G, ATP6V0A, and ATP6V0D of the V-ATPase are present in the epididymal and vas deferens epithelium. Our results confirm that narrow and clear cells are well fit for active proton secretion. In addition, the diverse functions of the V-ATPase may be established through the utilization of specific subunit isoforms. In principal cells, the ATP6V0D1 isoform may have a physiological function that is distinct from its role in proton transport via the V-ATPase complex.