Identification and regulation of K+ and Cl- channels in human parotid acinar cells

The properties of K+ channels in these cells were studied using patch-clamp methods. Two channels, with conductances of 165+/-13 pS (n=6) and 30+/-1 pS (n=3), were identified in single-channel experiments. In cell-attached patches the reversal potentials were -67+/-8 and -74+/-2 mV for the large and small conductance channel, respectively, suggesting that both channels are K+-selective. The large conductance channel was also shown to be K+-selective in inside-out patches. The open probability (P(o)) of this channel was increased at depolarizing potentials and by increasing intracellular Ca2+ concentration ([Ca2+]i). These properties suggest that the large conductance channel is a 'maxi' Ca2+-activated K+ channel (BK(Ca)). The small conductance channel was not observed in inside-out patches. Carbachol (CCh; 10(-5) M) activated the BK(Ca) channel, but not the small conductance channel, in cell-attached patches. CCh also caused a dose-dependent increase in [Ca2+]i measured by fura-2 in microspectrofluorimetric studies, with a half-maximal response at approximately 3x10(-6) M. Neither isoproterenol (10(-5) M) nor substance P (10(-6) M) affected K+-channel activity or [Ca2+]i. In whole-cell experiments, CCh caused an increase in outward current. Charybdotoxin (10(-7) M), a BK(Ca) blocker, inhibited a large component of the CCh-induced current. A large component of the charybdotoxin-insensitive current may be carried by Ca2+-activated Cl- channels, which were also observed in human parotid acinar cells. The results indicate that BK(Ca) channels make a significant contribution to the whole-cell conductance in human parotid acinar cells.