Electrogenic anion secretion in cultured rat epididymal epithelium

Primary monolayer cultures enriched with principal cells from rat cauda epididymis were grown on pervious supports until confluence was reached. The epithelia so formed were used for short-circuit current recording. Epididymal monolayers had a transepithelial potential of 0.2 mV (apical side negative), a basal short-circuit current of 2 microA/cm2 and a transepithelial resistance of 60-90 omega cm2 when bathed on both sides with Krebs-Henseleit solution at 37 degrees C and gassed with 95% O2-5% CO2. 8-bromo-adenosine 3',5'-phosphate (1 mM) and forskolin (10 microM) caused an inward-flowing current in short-circuited monolayers. The current was partially sensitive to acetazolamide and to frusemide, suggesting that anion secretion was responsible for the responses. In the absence of chloride in the bathing fluid the response to forskolin was sensitive to acetazolamide but not to frusemide. The peptide lysylbradykinin (LBK) and prostaglandin E2 (PGE2) also produced inward-flowing currents which again appeared to be due to anion secretion. The actions of PGE2 were seen only when this agent was added to the basolateral side of the tissue, while LBK had effects from both sides. The responses to kinin, but not to PGE2, were inhibited by cyclo-oxygenase inhibitors such as piroxicam and indomethacin. It seems the kinin effects are dependent, at least in part, upon eicosanoid formation. Responses to kinin and PGE2 were severely attenuated in chloride-free bathing solution. Readdition of chloride-containing solution restored the responses to both agents. Assuming electrogenic ion secretion in the epididymis is accompanied by osmotic fluid flow it is evident that the transit time of sperm in the cauda epididymis will be reduced. Possible consequences for the maturation of spermatozoa are discussed.