PROTON SECRETION IN THE MALE REPRODUCTIVE-TRACT - INVOLVEMENT OF CL--INDEPENDENT HCO3- TRANSPORT

The lumen of the epididymis is the site where spermatozoa undergo thei r final maturation and acquire the capacity to become motile. An acidi c luminal fluid is required for the maintenance of sperm quiescence an d for the prevention of premature activation of acrosomal enzymes duri ng their storage in the cauda epididymis and vas deferens. We have pre viously demonstrated that a vacuolar H+-ATPase [proton pump (PP)] is p resent in the apical pole of apical and narrow cells in the caput epid idymis and of clear cells in the corpus and cauda epididymis and that this PP is responsible for the majority of proton secretion in the pro ximal 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 ac etazolamide markedly inhibits the rate of proton secretion by 46.2 +/- 6.1%. The rate of acidification was independent of Cl- and was strong ly inhibited by SITS under both normal and Cl--free conditions (50.6 /- 5.0 and 57.5 +/- 6.0%, respectively). In the presence of Cl-, diphe nylamine-2-carboxylate (DPC) had no effect, whereas SITS inhibited pro ton secretion by 63.7 +/- 11.3% when applied together with DPC. In Cl- free solution, DPC markedly inhibited proton efflux by 45.1 +/- 7.6%, SITS produced an additional inhibition of 18.2 +/- 6.6%, and bafilomy cin had no additive effect. In conclusion, we propose that CAII plays a major role in proton secretion by the proximal vas deferens. Acidifi cation does not require the presence of Cl-, but DPC-sensitive Cl- cha nnels might contribute to basolateral extrusion of HCO, under Cl--free conditions. The inhibition by SITS observed under both normal and Cl- -free conditions indicates that a Cl-/HCO3- exchanger is not involved and that an alternative HCO3- transporter participates in proton secre tion in the proximal vas deferens.