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 (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 gj decreased slightly with increasing Vj. 3. The gap junction currents (Ij) declined with time following a single exponential. The time constants of Ij inactivation (taui) decreased with increasing Vj. 4. Single channels exhibited a main state, a residual state and a closed state. The conductances gammaj,main and gammaj,residual were 179 and 48 pS, respectively (pipette solution, potassium aspartate; temperature, 36-37 degrees C; extrapolated to Vj = 0 mV). 5. The conductances gammaj,residual and gammaj,main showed a slight Vj dependence and were sensitive to temperature (Q10 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 (Po) at steady state decreased from 1 to 0 with increasing Vj (Boltzmann fit: Vj,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 Vj 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.

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