Cardiac gap junction channel activity in embryonic chick ventricle cells

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Abstract
We have recorded single-gap junction-channel currents from pairs of 7-day chick embryo ventricle cells, using the double whole cell patch-clamp technique. Junctional conductance (Gj) was variable from one preparation to the next, ranging from 0.15 to 35.0 nS. Single-channel conductance (.gamma.j) of the main junctional channel was 166 .+-. 51 pS and was independent of Gj; a second conductance level of 60-80 pS was also seen in favorable records. The transition time from the closed to the open state was 285 .+-. 153 .mu.s, with some slow transitions lasting 1-5 ms. Channels opened and closed stochastically; Gj could be defined by the product of the number of active channels in the junction (N), the mean open-state probability (Po) of the channels, and .gamma.j. Channel activity was unaffected by cell membrane potential or by transjunctional potential. Po and Gj were reversibly reduced to low levels by 1-octanol or by elevated [Caj], whereas .gamma.j was unchanged by these agents. The 60-80 pS conductance mechanism was octanol- and Ca-resistant, but it is not clear whether this represents a subconductance level of the main channel or a separate class of smaller channels.