Figure 2.

Multiple CaVs per BK_Ca-CaV complex. (A) Shown here is the Markov chain model for complexes with k noninactivated CaVs. (B) Shown here are steady-state BK_Ca activation functions (upper) and time constants (lower) for BK_Ca channels in complexes with 1 (cyan), 2 (green), or 4 (red) CaVs given from Eq. 26 (see Eq. S36 for the details; solid) or from the approximation defined by Eq. 29 (dashed). The gray dashed curve shows the CaV activation function m_CaV,∞, for comparison. (C) Shown here are simulated BK_Ca open probabilities in response to a voltage step from −80 to 0 mV, obtained from Monte Carlo simulations of the Markov model of n inactivating independent CaVs controlling a BK_Ca channel (black), from the ODE model of all states in (A) coupled to CaV inactivation (Eq. 27; Eqs. S19–S25; solid blue), from the reduced ODE model considering CaV activation kinetics ((26), (27); dashed red), and from the simplification assuming m_CaV = m_CaV,∞ ((29), (27); dash-dotted green). To see this figure in color, go online.