FIGURE 7.

CytC and CT9 influence InsP₃Rs and connexin hemichannels, respectively. A, CytC binds to the C-terminal domain of InsP₃R. B, InsP₃Rs have a bell-shaped [Ca²⁺]_i dependence of the open probability (Po) with below 250 nm concentrations potentiating InsP₃R opening and higher concentrations acting inhibitory. The bell-shaped dose response curve is derived from parameters and equations described in Ref. 97 for InsP₃R type 1. CytC binds to InsP₃R and removes the inhibitory effects of high [Ca²⁺]_i on InsP₃R open probability. C, CT9 peptide is composed of the last 9 amino acids of the Cx43 C terminus and interacts with a sequence on the intracellular loop (IL). EC, extracellular. D, Ca²⁺ activation of hemichannels composed of Cx43 are characterized by a bell-shaped [Ca²⁺]_i dependence (hemichannel ATP release and dye uptake studies, derived from data in Ref. 36). CT9 peptide removes the declining phase at [Ca²⁺]_i above 500 nm (37).