PROPERTIES OF CAMP-DEPENDENT AND CA2-DEPENDENT WHOLE-CELL CL- CONDUCTANCES IN RAT EPIDIDYMAL CELLS()

Single rat epididymal cell studied under whole cell patch-clamp condit ion responded to 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monopho sphate (CPT-cAMP) (500 muM) and to ionomycin (1 muM) by an increase in whole cell conductance. A major part of the stimulated current was ca rried by Cl-, although a small part was due to nonselective cation cur rent. After elimination of the cation current component by using imper meant cation, the cells revealed different Cl- conductance properties in response to adenosine 3',5'-cyclic monophosphate (cAMP) and ionomyc in. The cAMP-stimulated Cl- conductance was independent of time and vo ltage and showed a linear current-voltage relationship. The anion perm selectivity was NO3- > Br- > Cl-almost-equal-to I- much greater than S O42-. The ionomycin-stimulated Cl-conductance showed marked time and v oltage dependency. In contrast to the cAMP-induced anion permselectivi ty, the ionomycin-induced anion permselectivity was I- > Br- almost-eq ual-to NO3- > Cl- much greater than SO42-. These results indicate that the epididymal epithelial cells exhibit different Cl- conductances se nsitive to cAMP and Ca2+. The cAMP-activated conductance has propertie s resembling the type associated with the cystic fibrosis transmembran e conductance regulator found in cystic fibrosis-affected epithelia. T his finding supports the notion that the epididymis is a cystic fibros is epithelium.