Regulation of WT Cx26 and A40V and G45E mutant hemichannels by voltage and extracellular Ca²⁺. Representative conductance-voltage (G-V) relationships are shown expressed in Xenopus oocytes at different external Ca²⁺ concentrations ranging from nominal (0 added) to 2 mM obtained by applying slow (3 min) voltage ramps from 50 to −100 mV to oocytes expressing WT Cx26 (A), G45E (B), or A40V (C). The holding potential before and after each ramp was maintained at −20 mV. All conductances were normalized to the maximum value measured in 0 Ca²⁺. In WT and both mutant hemichannels, conductance declined strongly with hyperpolarization except in low extracellular Ca²⁺. Increasing Ca²⁺ shifted activation in the depolarizing direction in all cases. However, both mutant hemichannels appeared less sensitive to the effects of Ca²⁺, particularly at low Ca²⁺ concentrations. This reduced sensitivity to Ca²⁺ was strongest in A40V. In addition, G45E hemichannels showed stronger voltage-dependent closure at positive voltages (up to 50 mV).