Figure 1.

Mg²⁺-dependent modulation of g_j and V_j-gating in HeLa cells expressing Cx36-EGFP GJs. A, C, Bottom, Dynamics of g_j (normalized to initial g_j value) during repeated V_j ramps (+20–−20 mV and 1.3 s in duration; top traces) at [Mg²⁺]_p = 0.01 (A) and 5 mm (C). B, D, g_j–V_j dependence (normalized to initial g_j value at V_j = 0) obtained during 50-s-long V_j ramps (from 0 to −100 mV; middle traces) derived from data shown in A and C, respectively; the numbers on the g_j–V_j plots correspond to numbers on g_j traces in A and C. Fitted curves shown in color were obtained using the S16SM. Gray lines show fitted curves obtained from control g_j–V_j plots ([Mg²⁺]_p = 1 mm). E, Concentration–response relation of g_j (normalized to initial g_j value) as a function of [Mg²⁺]_p; EC₅₀ ≈ 0.45 mm. Averaged data are shown in colored circles. Data of individual experiments are shown in gray triangles. Roman numerals correspond to different solutions shown in Table 1. F, Averaged g_j–V_j dependencies (normalized to g_j value at V_j = 0) obtained at different [Mg²⁺]_p (curves in black) were fitted using a S16SM (g_j–V_j plots in colors). Roman numerals correspond to different Mg²⁺ concentrations shown in E. Parameters obtained after fitting are shown in Table 2. G–I, Open probabilities of fast and slow gates in α and β aHCs (P_oF,α, P_oS,α and P_oF,β, P_oS,β, respectively) depending on V_j were calculated using parameters obtained in F for [Mg²⁺]_p = 0.01 (G), 1 (H), and 10 mm (I).