Effects of intracellular K+ and Rb+ on gating of embryonic rat telencephalon Ca2+-activated K+ channels

We have investigated the effects of intracellular K+ and Rb+ on single-channel currents recorded from the large-conductance Ca+2-activated K+ (BK) channel of the embryonic rat telencephalon using the inside-out patch-clamp technique, Our novel observation concerns the effects of these ions on rapid flickering of channel openings, Specifically, flicker gating was voltage dependent, i.e., it was reduced by depolarization in the -60 to -10 mV range with equimolar concentrations of K+ ions (150 K-0(+)/150K(i)(+)). Removal of K-i(+) resulted in significant flickering at all potentials in this voltage range, In other words, the voltage dependence of flicker gating was effectively eliminated by the removal of K-i(+). This suggests that a K+ ion entering the channel from the intracellular medium binds, in a voltage-dependent manner, at a site that locks the flicker gate in its open position, No effects of changes in K-i(+) were observed on the primary, voltage-dependent gate of the channel, The change in flickering did not cause a change in the mean burst duration, which indicates that the primary gate is stochastically independent of the flicker gate. Intracellular Rb+ can substitute for-and is even more effective than-K-i(+) with regard to suppression of flickering. Substitution of Rb-i(+) for K-i(+) also increased the mean burst duration for V greater than or equal to -30 mV. Both effects of Rb-i(+) were removed by membrane hyperpolarization.