Proton secretion in the male reproductive tract: involvement of Cl2-independent HCO3

Breton, Sylvie, Katherine Hammar, Peter J. S. Smith, and Dennis Brown. Proton secretion in the male reproductive tract: involvement of Cl2-independent HCO3 2 transport. Am. J. Physiol. 275 (Cell Physiol. 44): C1134–C1142, 1998.— The lumen of the epididymis is the site where spermatozoa undergo their final maturation and acquire the capacity to become motile. An acidic luminal fluid is required for the maintenance of sperm quiescence and for the prevention of premature activation of acrosomal enzymes during their storage in the cauda epididymis and vas deferens. We have previously demonstrated that a vacuolar H1-ATPase [proton pump (PP)] is present in the apical pole of apical and narrow cells in the caput epididymis and of clear cells in the corpus and cauda epididymis and that this PP is responsible for the majority of proton secretion in the proximal vas deferens. We now show that PP-rich cells in the vas deferens express a high level of carbonic anhydrase type II (CAII) and that acetazolamide markedly inhibits the rate of proton secretion by 46.2 6 6.1%. The rate of acidification was independent of Cl2 and was strongly inhibited by SITS under both normal and Cl2-free conditions (50.6 6 5.0 and 57.5 6 6.0%, respectively). In the presence of Cl2, diphenylamine-2-carboxylate (DPC) had no effect, whereas SITS inhibited proton secretion by 63.7 6 11.3% when applied together with DPC. In Cl2-free solution, DPC markedly inhibited proton efflux by 45.1 6 7.6%, SITS produced an additional inhibition of 18.2 6 6.6%, and bafilomycin had no additive effect. In conclusion, we propose that CAII plays a major role in proton secretion by the proximal vas deferens. Acidification does not require the presence of Cl2, but DPC-sensitive Cl2 channels might contribute to basolateral extrusion of HCO3 2 under Cl2-free conditions. The inhibition by SITS observed under both normal and Cl2-free conditions indicates that a Cl/HCO3 2 exchanger is not involved and that an alternative HCO3 2 transporter participates in proton secretion in the proximal vas deferens.