Figure 5.

The proposed kinetic mechanism for Ca²⁺ and voltage regulation of Cx46 hemichannels. (A) The complete model considers three voltage-dependent transitions form O to C1 to C2 and C3, given by the equilibrium constants K1 and the rates α, β, χ and δ. Binding of Ca²⁺ occurs only in the closed states and is given by the association constant Ka (1/Kd), m indicates the number of binding sites. Voltage gating and Ca²⁺ binding are allosterically coupled by the coupling constant C and its kinetic factors c _b and c _f. The black arrows indicate rate-limiting steps and gray arrows indicate transitions in equilibrium.(B) The complete model can be collapsed into a simpler model in which each state contains several substates that are in equilibrium. The equations that govern this model are presented.