Gating Mechanism of BK (Slo1) Channels : So Near, Yet So Far

Large conductance calcium- and voltage-activated K⁺ channels (Slo1), also referred to as “BK” or “maxi K” channels because of their high single channel conductance (250–300 pS in symmetrical 150 mM KCl), are widely distributed in many different tissues (Kaczorowski et al., 1996). A signature feature of BK channels, in addition to their high K⁺ selectivity and conductance, is that they are activated in a highly synergistic manner by both intracellular calcium ion (Ca²⁺_i) and depolarization (Marty, 1981; Pallotta et al., 1981; Barrett et al., 1982; Latorre et al., 1982). This is shown in Fig. 1, which plots channel open probability Po (z axis) versus Ca²⁺_i (y axis) and membrane potential (x axis). It is this synergistic activation that allows BK channels to play key roles in controlling excitability in a...