Figure 3.

Interactions between V_j and V_m gating. (A) Effect of V_m on V_j dependence. Records of junctional currents (I_j) elicited by the same V_j steps (±100 mV by 20 mV increments and 30 s duration) applied at two holding potentials (V_m = 0 and −80 mV). The V_m difference changed junctional conductance from g_{j(0 mV)} = 2.72 μS to g_{j (−80 mV)} = 4.80 μS, but the junctional currents declined for increasing positive and negative V_j steps with similar characteristics (positive I_j are shown upward). (B) Plots of G_jss/V_j relations normalized to g_j at 0 (○) and −80 mV (●) were essentially superimposable, indicating that V_j gating was little affected by V_m. (C) Effect of V_j on V_m dependence. Sample records of junctional currents (I_j) after subtraction of nonjunctional currents evoked by the same V_m protocol as in Fig. 1 for V_j = 0 (left) and V_j = +80 mV (right) in pairs expressing WT and truncated S257stop junctions. Conductances at the two holding potential were g_j(Vj = 0) = 8.31 and g_j(Vj = 80) = 1.57 μS for WT junctions and g_j(Vj = 0) = 10.81 to g_j(Vj = 80) = 1.27 μS for S257stop junctions. With V_j = 0 mV, equal depolarization of both cells equally decreased g_j of WT and of S257stop junctions. However, when g_j was reduced at V_j = +80 mV, V_m sensitivity of WT junctions was markedly reduced, whereas sensitivity of S257stop junctions in which the fast V_j gate was removed (18) was little affected. For comparison, current gains are increased for the V_j = +80 mV records. (D) G_jss/V_m relations of WT (○) and truncated S257stop (●) junctions for V_j = +80 where G_j is normalized to the value at V_m*. The curves are fits of the squared Boltzmann relations with parameters of Table 1. Each point represents mean values (±SEM) of four pairs. (E) Gating model for the combined V_j and V_m dependence of Cx43 junctions. See Discussion.