Figure 8.

Voltage likely affects the affinity of the BK_Ca channel for Ca²⁺. Shown are a series of mSlo1α G-V relations determined at the following [Ca²⁺]: 0.003, 0.070, 0.130, 0.360, 0.8, 10, and 100 μM and fitted simultaneously with the HA model modified to include two Ca²⁺ binding sites (Bao et al., 2002; Horrigan and Aldrich, 2002). Using values determined from this and previous experiments in our laboratory (Bao and Cox, 2005), the parameters were held as follows: K_O1 = 0.88 μM, K_C1 = 3.18 μM, K_O2 = 4.88 μM, K_C2 = 23.2 μM, L_O = 2.2 × 10⁻⁶, z_L= 0.41 e, V_hc = 151 mV, V_ho = 27 mV, and z_J = 0.58 e. In A, the values of allosteric factors E₁ and E₂ were held to a value of 1 for both Ca²⁺ binding sites A and B. In B, the values of E₁ and E₂ were allowed to vary. The best fit values of E₁ and E₂ were 1.43 and 1.73, respectively.