The ACh-induced whole-cell currents in sheep parotid secretory cells. Do BK channels really carry the ACh-evoked whole-cell K+ current?

As in other salivary glands, the secretory cells of the sheep parotid have a resting K+ conductance that is dominated by BK channels, which are activated by acetylcholine (ACh) and are blocked by tetraethylammonium (TEA). Nevertheless, perfusion studies indicate that TEA does not inhibit ACh-evoked fluid secretion or K+ efflux from intact sheep parotid glands. In the present study, we have used whole-cell patch clamp techniques to show that ACh activates K+ and Cl− conductances in sheep parotid secretory cells by increasing intracellular free Ca2+, and we have compared the blocker sensitivity of the ACh-evoked whole-cell K+ current to the previously reported blocker sensitivity of the BK channels seen in these cells.