Expression of cystic fibrosis transmembrane conductance regulator in rat efferent duct epithelium

The expression of cystic fibrosis transmembrane conductance regulator (CFTR ) was studied in rat efferent ducts. Under Whole-cell patch-clamp condition , efferent duct cells responded to intracellular cAMP with a rise in inward current. The cAMP-activated current exhibited a linear I-V relationship an d time- and voltage-independent characteristics. The current was inhibited by the CI= channel blocker diphenylamine 2,2 ' -dicarboxylic acid (DPC) in a voltage-dependent manner and reversed at 24 +/- 0.5 mV, close to the equi librium potential for CI- (30 mV), suggesting that the current was CI- sele ctive. The cAMP-activated current displayed a permeability sequence of Br- > CI- > I-. Short-circuit current measurement in cultured rat efferent duct epithelia also revealed a cAMP-activated inward current inhibitable by DPC . These electrophysiological properties of the cAMP-activated CI- conductan ce in the efferent duct were consistent with those reported for CFTR. In su pport of the functional studies, reverse transcription polymerase chain rea ction revealed the presence of CFTR message in cultured efferent duct epith elium. Immunohistochemical studies in intact rats also demonstrated CFTR pr otein at the apical membrane of the principal cells of efferent duct. CFTR may play a role in modulating fluid transport in the efferent duct.