The purpose of this study was to characterize the ion conductances, in particular those for Cl- and K+, of human sweat duct cells grown in primary culture. Sweat duct cells from healthy individuals were grown to confluence on a dialysis membrane, which was then mounted in a mini-Ussing chamber and transepithelial and intracellular potentials were measured under open-circuit conditions. Under control conditions the epithelia developed mucosa-negative transepithelial potentials, Vte, of about -10 mV. The apical membrane potential, Va, was -25 mV to -30 mV (n = 97) in most cells, but several cells had a higher potential of about -55 mV (n = 29). Mucosal amiloride (10 mumol/l) hyperpolarized Va from -31 +/- 1 mV to a new sustained level of -46 +/- 2 mV (n = 36). These changes were accompanied by increase in the fractional resistance of the apical membrane, fRa, and decreases of Vte and the equivalent short-circuit current, Isc. In amiloride-treated tissues an increase in mucosal K+ concentration (5 mmol/l to 25 mmol/l) depolarized Va by 5 +/- 1 mV (n = 8), while the same step on the serosal side depolarized Va by 20 +/- 2 mV (n = 8). A Cl- channel blocker 3',5-dichlorodiphenylamine-2-carboxylate DCl-DPC; 10 mumol/l) depolarized Va by 5 +/- 1 mV (n = 6), an effect that was lost after amiloride application. The blocker had no effect from the serosal side. Reduction of mucosal Cl- (from 120 to 30 or 10 mmol/l) depolarized Va by 9-11 mV (n = 35), an effect that was often followed by a secondary hyperpolarization of 10-30 mV (n = 27).(ABSTRACT TRUNCATED AT 250 WORDS)