Biophysical properties of mouse connexin30 gap junction channels studied in transfected human HeLa cells

1Human HeLa cells expressing mouse connexin30 (Cx30) were used to study the electrical properties of Cx30 gap junction channels. Experiments were performed on cell pairs with the dual voltage‐clamp method.2The gap junction conductance (gj) at steady state showed a bell‐shaped dependence on junctional voltage (Vj; Boltzmann fit: Vj,0= 27 mV, gj,min= 0.15, z= 4). The instantaneous gjdecreased slightly with increasing Vj.3The gap junction currents (Ij) declined with time following a single exponential. The time constants of Ijinactivation (τi) decreased with increasing Vj.4Single channels exhibited a main state, a residual state and a closed state. The conductances γj,mainand γj,residualwere 179 and 48 pS, respectively (pipette solution, potassium aspartate; temperature, 36‐37 °C; extrapolated to Vj= 0 mV).5The conductances γj,residualand γj,mainshowed a slight Vjdependence and were sensitive to temperature (Q10values of 1.28 and 1.16, respectively).6Current transitions between open states (i.e. main state, substates, residual state) were fast (< 2 ms), while those between an open state and the closed state were slow (12 ms).7The open channel probability (Po) at steady state decreased from 1 to 0 with increasing Vj(Boltzmann fit: Vj,0= 37 mV; z= 3).8Histograms of channel open times implied the presence of a single main state; histograms of channel closed times suggested the existence of two closed states (i.e. residual states).9We conclude that Cx30 channels are controlled by two types of gates, a fast one responsible for Vjgating involving transitions between open states (i.e. residual state, main state), and a slow one correlated with chemical gating involving transitions between the closed state and an open state.