Steady-state Ca²⁺ response curves show that A40V hemichannels are less sensitive to external Ca²⁺ than WT Cx26 and G45E hemichannels. (A) Examples of recordings of WT Cx26 (top) and A40V (bottom) hemichannel currents and effects of increasing concentrations of extracellular Ca²⁺ (0, 0.2, 0.3, 0.5, 1.0, 2.0, and 5.0 mM). Oocytes were voltage clamped and maintained at −40 mV throughout. (B) Summary of data for WT Cx26 (■), A40V (∇), and G45E (○) compiled from several experiments such as that shown in A. Each point is the mean ± SEM of ∼20 experiments. (C) Plot showing resting membrane potentials measured in oocytes 24–48 h after RNA injection for WT Cx26 (■), A40V (∇), and G45E (○). Each point represents a measurement from an individual oocyte. Horizontal lines represent means of −25.1 ± 9.4 mV, −13.1 ± 5.5 mV, and −22.3 ± 8.0 mV for WT Cx26, A40V, and G45E, respectively. (D) The left panel shows the mean holding currents for oocytes from C when initially clamped to −40 mV. A40V-expressing oocytes, which showed the lowest resting potentials, showed the largest holding currents. The same oocytes exposed to 0 added Ca²⁺ (right) showed similar maximum current levels, indicating similar levels of expression.