Kinetic Gating Mechanisms for Bk Channels : When Complexity Leads to Simplicity

Large conductance calcium-activated K⁺ channels, also referred to as “BK” or “maxi K” channels because of their big single-channel conductance (∼300 pS in symmetrical 150 mM KCl) are widely distributed in many different tissues (Latorre 1994; Kaczorowski et al. 1996). A signature feature of BK channels, in addition to their high K⁺ selectivity and conductance, is that they are activated by both intracellular calcium ion (Ca²⁺_i) and depolarization in a highly synergistic manner (Marty 1981; Barrett et al. 1982). It is this synergistic interaction that elevates BK channels to be guardians of calcium-driven processes and protectors of cellular integrity. Although Ca²⁺_i serves as a key messenger to trigger processes such as muscle contraction and secretion of transmitters, prolonged elevated Ca²⁺_i can be detrimental to...