title: Electrical properties of gap junction hemichannels identified in transfected HeLa cells.
abstract: 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.
authors.affiliation: Department of Physiology, University of Bern, Switzerland.
authors.forename: V
authors.initials: V
authors.lastname: Valiunas
authors.forename: R
authors.initials: R
authors.lastname: Weingart
mesh_terms: D000818:Animals; D000075302:Connexin 30; D017630:Connexins / Q000235:genetics* / Q000378:metabolism*; D004553:Electric Conductivity; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D017629:Gap Junctions / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D007700:Kinetics; D051379:Mice; D018408:Patch-Clamp Techniques; D013696:Temperature; D014162:Transfection; D000099264:Connexin 50
chemical_list: D000075302:Connexin 30; D017630:Connexins; D005136:Eye Proteins; D000099264:Connexin 50; C491020:GJB6 protein, human; C100629:Gjb6 protein, mouse; C082917:GJA3 protein, human