Inhibition by chloride channel blockers of anion secretion in cultured epididymal epithelium and intact epididymis of rats.

1. Anion secretion by primary monolayer cultures of rat epididymal cells was studied by the short circuit current technique. 2. Monolayers had a transepithelial potential difference of 1.34 mV, apical side negative and a short circuit current of 2.45 microA cm-2. The transepithelial resistance was 504 omega cm2. 3. Addition of anthracene-9-carboxylate (9-AC) to the apical side caused a biphasic response, a decrease followed by an increase in the short circuit current (SCC) which then returned to the basal level. Addition of 9-AC to the basolateral side also caused a biphasic response but the increase in current was sustained. 4. Addition of diphenylamine-2-carboxylate (DPC) and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) caused an inhibition of the SCC when added to the apical or basolateral side. 5. When the epithelium was stimulated with adrenaline (0.23 microM, basolaterally), the SCC rose to a peak value of 10.36 microA cm-2 and then stabilized at 3.82 microA cm-2 after 15 min. Addition of 9-AC to the apical side caused a triphasic response: a decrease, reversal to the original level followed by a slow inhibition which was sustained. The inhibition achieved at the steady state was concentration-dependent with an apparent IC50 value of 2.51 mM. Addition of 9-AC to the basolateral side produced a similar response but a time lag of 20 s was observed. 6. DPC and NPPB also caused the SCC to decrease when added to the apical side of the monolayers stimulated with adrenaline. The IC50 values 0.148 mM and 0.049 mM for DPC and NPPB, respectively. Basolateral application also caused an inhibition but higher concentrations were required to inhibit 50% of the adrenaline stimulated SCC. 7. Serosal to mucosal flux of chloride was studied in intact epididymis luminally perfused in vivo. 9-AC added to the luminal perfusion solution inhibited the C1 flux in a dose-dependent manner with an IC50 value similar to that observed in cultured epithelium in vitro. 8. It is concluded that anion secretion by the epididymal cells may conform to models proposed for other Cl secreting epithelia and may involve anion diffusion across the apical channels which are blocked by Cl channel blockers.