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

1 Human 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. 2 The gap junction conductance ( g j ) at steady state showed a bell‐shaped dependence on junctional voltage ( V j ; Boltzmann fit: V j,0 = 27 mV, g j,min = 0.15, z = 4 ). The instantaneous g j decreased slightly with increasing V j . 3 The gap junction currents ( I j ) declined with time following a single exponential. The time constants of I j inactivation (τ i ) decreased with increasing V j . 4 Single channels exhibited a main state, a residual state and a closed state. The conductances γ j,main and γ j,residual were 179 and 48 pS, respectively (pipette solution, potassium aspartate; temperature, 36‐37 °C; extrapolated to V j = 0 mV). 5 The conductances γ j,residual and γ j,main showed a slight V j dependence and were sensitive to temperature ( Q 10 values of 1.28 and 1.16, respectively). 6 Current 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). 7 The open channel probability ( P o ) at steady state decreased from 1 to 0 with increasing V j (Boltzmann fit: V j,0 = 37 mV; z = 3 ). 8 Histograms 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). 9 We conclude that Cx30 channels are controlled by two types of gates, a fast one responsible for V j gating 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.