Ca²⁺-activated Cl^- channel currents in rat ventral prostate epithelial cells

BACKGROUND. In many epithelial tissues, the Cl^- efflux via Ca²⁺-activated Cl^- channels (Cl_Ca) play a key role for the fluid secretion. To elucidate the mechanism of prostatic fluid secretion, the properties of whole-cell chloride conductance were investigated. MATERIALS AND METHODS. Rat prostate secretory epithelial cells (RPSECs) were isolated by collagenase treatment, and were used for the whole-cell voltage clamp. Both extra- and intracellular monovalent cations were replaced by N-methyl-D-glucamate to record the Cl^- current selectively. RESULTS. A bath application of Ca²⁺-ionophore, ionomycin (0.2 μM), increased the membrane conductance with outwardly rectifying voltage-dependence. On step-like depolarization from -60 to +80 mV (500 msec), the ionomycin-induced current showed slowly activating kinetics, a known property of Cl_Ca current (I_Cl(Ca)) of other tissues. The relative permeability of Cl_Ca to various anions was calculated from the reversal potentials measured under a total replacement of extracellular Cl^- with various anions, and the relative order of permeability was SCN^- > I^- > Br^- > Cl^- ≫ gluconate. The amplitude of I_Cl(Ca) was decreased by various anion channel blockers: niflumic acid (100 μM), DPC (100 μM), DIDS (1 mM), and NPPB (200 μM). CONCLUSIONS. RPSECs have Cl_Ca that may provide Cl^- efflux pathways for the exocrine secretions of the prostate.