Slow gating of gap junction channels and calmodulin

Certain COOH-terminus mutants of connexin32 (Cx32) were previously shown to form channels with unusual transjuctional voltage (V-j) sensitivity when t ested heterotypically in oocytes against Cx32 wild type. Junctional conduct ance (G(j)) slowly increased by severalfold or decreases to nearly zero wit h Vj positive or negative, respectively, at mutant side, and V-j positive a t mutant side reversed CO2-induced uncoupling. This suggested that the CO2- sensitive gate might be a V-j-sensitive slow gate. Based on previous data f or calmodulin (CaM) involvement in gap junction function, we have hypothesi zed that the slow gate could be a CaM-like pore plugging molecule (cork gat ing model). This study describes a similar behavior in heterotypic channels between Cx32 and each of four new Cx32 mutants modified in cytoplasmic-loo p and/or COOH-terminus residues. The mutants are: ML/NN+-3R/N, 3R/N, ML/NN and ML/EE; in these mutants, N or E replace M105 and L106, and N replace R2 15, R219 and R220. This study also reports that inhibition of CaM expressio n strongly reduces V-j and CO2 sensitivities of two of the most effective m utants, suggesting a CaM role in slow and chemical gating.