Figure 2.

Residual Cx30-mediated cation conductance in the presence of divalent cations (Ca²⁺, Mg²⁺) in the extracellular solution.A and B, representative whole-cell current traces recorded in a human Cx30 expressing oocyte (A) or in a control oocyte (B). Oocytes were superfused with standard bath solution (NaCl, open bars) or solution in which Na⁺ was replaced by NMDG⁺ (NMDG-Cl, grey bar). Dashed lines indicate zero current level. Continuous holding potential was −60 mV. Before, during, and after exposure to NMDG⁺ bath solution, voltage step protocols were performed with nine consecutive 2 s voltage steps in 20 mV increments starting with a hyperpolarizing pulse to −120 mV. Insets show overlays of resulting whole-cell current traces obtained at different holding potentials. C and D, Left panels, current data from the final 100 ms portion of each pulse were taken from similar experiments as shown in A and B, respectively, to construct corresponding average I/V curves. Mean and SEM (n = 34; N = 4) are shown. Right panels, reversal potentials obtained from the same experiments summarized in left panels. Individual data points and mean ± SEM are shown. Lines connect data points from individual oocytes. ∗∗∗p < 0.001; paired Student’s t-test. E, Left panel, average I/V plots corrected for endogenous oocyte currents using the data from the experiments summarized in C and D. The average whole-cell current values measured in control oocytes were subtracted from the corresponding individual whole-cell current values measured in oocytes from the same batch expressing Cx30. Right panel, reversal potentials obtained in the same experiments as summarized in the left panel. Individual data points and mean ± SEM are shown. ∗∗∗p < 0.001; paired Student’s t-test. F and G, representative overlays of whole-cell current traces resulting from similar voltage step protocols as described in A and B are shown from an oocyte expressing Cx30 (F) and from a control oocyte (G). For each oocyte current overlays are shown before (−carb) and 1 min after switching to a bath solution containing 1 mM carbenoxolone (+carb). H, current data from the final 100 ms portion of the pulses were taken from similar experiments as shown in F and G. Average I/V plots were constructed using carbenoxolone-sensitive current values (ΔI_carb), which were calculated by subtracting the current values recorded in the presence of carbenoxolone (+carb) from the corresponding current values recorded in its absence (−carb). Mean and SEM (Cx30: n = 21; N = 2; control: n = 27; N = 2) are shown.