Figure 4.

Electrophysiological characterization of Ca²⁺- and voltage-dependence of BK_Ca channels in human GCs (inside-out recordings). (A) BK_Ca current traces recorded at +60 mV and varying [Ca²⁺]_i (right). The closed channel state (c) corresponds to the respective lower current level (o, open state). (B) Ca²⁺-dependence of the channel open probability, P_o, at +70 mV. Data (black circles) represent means ± SEM of recordings from 30 cells and were fitted by a sigmoidal dose-response function with the bottom value fixed to be 0. EC₅₀ = 12 μM, Hill-slope = +0.8 μM (n = 30). Gray circles and fit curves show data from two individual recordings that represent extrema of Ca²⁺-dependence of P_o. (C) BK_Ca channel inactivation at [Ca²⁺]_i = 1 mM and +70 mV. (D) Voltage-dependence of P_o at [Ca²⁺]_i = 1 mM (V₅₀ = -54 mV, n = 4). Data were fitted by a Boltzmann sigmoidal function with bottom value fixed to be 0.