Figure 2.

Effects of mutations R243Q and D245Q on V_m gating. (A) Diagram of the topology of connexins (left). There are four transmembrane domains (M1–M4), two extracellular (E1, E2), cytoplasmic N- and C-terminal (NT, CT), and a cytoplasmic loop (CL). Amino acid sequence of the CT at its border with M4 (right) showing sites of the truncation mutants. The region between residues 242 and 257 contains one positively charged residue, Arg-243, and one negatively charged residue, Asp-245. (B) Sample records of nonjunctional and junctional currents as in Fig. 1 for mutants carrying single and double neutralizations (R243Q+D245Q, left; D245Q, center; and R243Q, right). The double mutation virtually abolished V_m sensitivity. The single mutations, D245Q and R243Q, increased and reduced dependence of g_j on V_m, respectively. (C) Graphs of G_jss/V_m relations. The curves are fits of the squared Boltzmann relations with parameters of Table 1. The g_j of junctions carrying the double R243Q+D245Q neutralization (▴) was not V_m sensitive. The single mutations, R243Q (■, broken line) and D245Q (●, dotted line), altered in opposite directions the steepness of V_m gating relative to WT (○, continuous line). The mutations also produced corresponding changes in V₀, the voltage for half change in the V_m sensitive component, relative to WT (Inset). Each point in C represents mean values (±SEM) of six pairs.