Using the patch-clamp technique, we have identified a large, outwardly rectifying, Cl--selective whole-cell current in primary cultures of human vas deferens epithelial cells. Whole-cell currents were time- and voltage-dependent and displayed inactivation following depolarising pulses >/= 60 mV. Currents were equally permeable to bromide (PBr/PCl = 1.05 +/- 0.04), iodide (PI/PCl = 1. 06 +/- 0.07) and Cl-, but significantly less permeable to gluconate (PGluc /PCl = 0.23 +/- 0.03). Currents spontaneously increased with time after establishing a whole-cell recording, but could be inhibited by exposure to a hypertonic bath solution which reduced inward currents by 68 +/- 4%. Subsequent exposure of the cells to a hypotonic bath solution led to a 418 +/- 110% increase in inward current, indicating that these currents are regulated by osmolarity. 4,4'-Diisothiocyanatostilbene-2,2'-disulphonic acid (100 microM) produced a rapid and reversible voltage-dependent block (60 +/- 5% and 10 +/- 7% inhibition of current, measured at +/- 60 mV, respectively). Dideoxyforskolin (50 microM) also reduced the volume-sensitive Cl- current, but with a much slower time course, by 41 +/- 13% and 32 +/- 16% (measured at +/- 60 mV, respectively). Tamoxifen (10 microM) had no effect on the whole-cell Cl- current. These results suggest that vas deferens epithelial cells possess a volume-sensitive Cl- conductance which has biophysical and pharmacological properties broadly similar to volume-sensitive Cl- currents previously described in a variety of cell types.