Multichannel recordings from membranes which contain gap junctions. II. Substates and conductance shifts.

Substates which can last up to several seconds are found in the 100-pS channel of the earthworm septum, a putative gap junction channel. The conductance of these substates is highly variable from preparation to preparation, and they are found at almost every fraction of the whole channel conductance. Another phenomenon seen in multichannel recordings is the "conductance shift": here the current passed by several open channels differs from an integral multiple of the current when only one channel is open. These shifts can be modelled by 1) a resistance in series with the channel or 2) long-lived substates. Each of these models fails in particular cases to explain either the magnitude or direction of the shifts. It is possible that both effects are simultaneously present.