Cardiac gap junction channel activity in embryonic chick ventricle cells.

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 microseconds, 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 [Cai], 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.