AROMATIC RESIDUES AFFECTING PERMEATION AND GATING IN DSLO BK CHANNELS

Structural determinants of permeation in large unit conductance calciu m-activated potassium channels (BK channels) were investigated. Y293 a nd F294 in the P-region of dSlo were substituted by tryptophans. Compa red to wild-type channels, Y293W channels displayed reduced inward uni tary currents while F294W channels exhibited normal inward current amp litudes but flickery kinetics. Both mutations produced changes in curr ent/voltage relations under bi-ionic conditions. Sensitivity to block by external tetraethylammonium (TEA) was affected in both channels, an d the voltage dependence of TEA block was increased in F294W channels. Both mutations also affected gating by shifting the half-maximal acti vation voltage of macroscopic conductance/voltage relations to more po sitive potentials, and eliminating a slow component of deactivation. T he double mutant did not produce ionic currents. These data are consis tent with a model in which Y293 contributes to a potassium-binding sit e close to the outer mouth of the dSlo pore, while F294 contributes to an energy barrier near this site.