Patch-clamp studies of K+ and Cl- channel currents in canine pancreatic acinar cells

K+ and Cl- channel currents in the plasma membrane of isolated canine pancreatic acinar cells were studied by patch-clamp single-channel and whole-cell current recording techniques. In excised inside-out patches, we found a Ca(2+)-activated (control range 0.01-0.4 microM) and voltage-activated K(+)-selective channel with a unit conductance of approximately 40 pS in symmetrical K(+)-rich solutions. In intact cells, addition of acetylcholine (1 microM) or bombesin tetradecapeptide (0.1 nM) to the bath evoked an increase in frequency of K+ channel opening. In whole-cell recordings on cells dialyzed with K(+)-rich and Ca(2+)-free solution containing 0.5 mM EGTA, the resting potential was about -40 mV. Depolarizing voltage pulses activated outward K+ currents, which were blocked by 10 mM tetraethylammonium, whereas hyperpolarizing pulses evoked smaller inward currents. Acetylcholine or bombesin activated the K+ current and enhanced the inward current, which was reduced by a low Cl- (10 mM) intracellular solution at -90 mV holding potential. These results suggest that both Ca(2+)- and voltage-activated K+ channels and Ca(2+)-activated Cl- channels exist in the plasma membrane of canine pancreatic acinar cells.