GAP-JUNCTIONS IN EXCITABLE CELLS

Gap junction channels are an integral part of the conduction or propag ation of an action potential from cell to cell. Gap junctions have rat her unique gating and permeability properties which permit the movemen t of molecules from cell to cell. These molecules may not be directly linked to action potentials but can alter nonjunctional processes with in cells, which in turn can affect conduction velocity. The data descr ibed in this review reveal that, for the majority of excitable cells, there are two limiting factors, with respect to gap junctions, that af fect the conduction/propagation of action potentials. These are (1) th e total number of channels and (2) the selective permeability of the c hannels. Interestingly, voltage dependence and the time course of volt age inactivation (kinetics) are not rate limiting steps under normal p hysiological conditions for any of the connexins studied so far. Only specialized rectifying electrical synapses utilize strong voltage depe ndence and rapid kinetics to permit or deny the continued propagation of an action potential.