期刊
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY
卷 440, 期 3, 页码 366-379出版社
SPRINGER VERLAG
DOI: 10.1007/s004240000294
关键词
connexin30; connexin46; connexin50; electrophysiology; gap junction; hemichannel
类别
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, 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 conductances, gamma(hc,main) and Y-hc.residual, the latter congruent to 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 probabili ty, P-o, was V-m-dependent. It declined from congruent to 1 at V-m = 0 mV to 0 at large V-m of either polarity. Hemichannel currents showed a voltage-dependent gamma(hc,main), i.e., it increased/decreased with hyperpolarization/depolarization. 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 inherent 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 closed under physiological conditions.
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