Electrical properties of gap junction hemichannels identified in transfected HeLa cells

Human HeLa cells transfected with mouse connexin Cx30, Cx46 or Cx50 were used to study the electrical properties of gap junction hemichannels. With no extracellular Ca2+, whole-cell recording revealed currents arising from hemichannels. Multichannel currents showed a time-dependent inactivation sensitive to voltage, Vm. Plots of the instantaneous conductance, ghc,inst, versus Vm were constant; plots of the steady-state conductance, ghc,ss, versus Vm were bell-shaped. Single-channel currents showed two conductances, gammahc,main and gammahc,residual, the latter approximately or approximately equals=1/6 of the former. Single-channel currents exhibited fast transitions (1-2 ms) between the main state and residual state. Late during wash-in and early during wash-out of 2 mM heptanol, single-hemichannel currents showed slow transitions between an open state and closed state. The open channel probability, Po, was Vm-dependent. It declined from approximately =1 at Vm= 0 mV to 0 at large Vm of either polarity. Hemichannel currents showed a voltage-dependent gammahc,main, i.e., it increased/decreased with hyperpolarization/depolarization. Extrapolation to Vm=0 mV led to a gammahc,main of 283, 250 and 352 pS for Cx30, Cx46 and Cx50, respectively. The hemichannels possess two gating mechanisms. Gating with positive voltage reflects Vj-gating of gap junction channels, gating with negative voltage reflects a property inherent to hemichannels, i.e., Vm or "loop" gating. We conclude that Cx30, Cx46 and Cx50 form voltage-sensitive hemichannels in single cells which are closed under physiological conditions.