Electrical properties of gap junction hemichannels identified in transfected HeLa cells

Human HeLa cells transfected with mouse connexin Cx30, Cx46 or Cx50 were us ed to study the electrical properties of gap junction hemichannels. With no extracellular Ca2+, whole-cell recording revealed currents arising from he michannels. Multichannel currents showed a time-dependent inactivation sens itive to voltage, V-m. Plots of the instantaneous conductance, g(hc.inst), versus V-m were constant; plots of the steady-state conductance, g(hc,ss), versus V-m were bell-shaped. Single-channel currents showed two conductance s, gamma(hc,main) and Y-hc.residual, the latter congruent to 1/6 of the for mer. Single-channel currents exhibited fast transitions (1-2 ms) between th e main state and residual state. Late during wash-in and early during wash- out of 2 mM heptanol, single-hemichannel currents showed slow transitions b etween an open state and closed state. The open channel probabili ty, P-o, was V-m-dependent. It declined from congruent to 1 at V-m = 0 mV to 0 at la rge V-m of either polarity. Hemichannel currents showed a voltage-dependent gamma(hc,main), i.e., it increased/decreased with hyperpolarization/depola rization. Extrapolation to V-m=0 mV led to a gamma(hc,main) of 283, 250 and 352 pS for Cx30, Cx46 and Cx50, respectively. The hemichannels possess two gating mechanisms. Gating with positive voltage reflects V-j-gating of gap junction channels, gating with negative voltage reflects a property inhere nt to hemichannels, i.e., V-m or "loop" gating. We conclude that Cx30, Cx46 and Cx50 form voltage-sensitive hemichannels in single cells which are clo sed under physiological conditions.