Electrical interactions among real cardiac cells and cell models in a linear strand.

Previous work with model systems for action potential conduction have been restricted to conduction between two real cells or conduction between a model cell and a real cell. The inclusion of additional elements to make a linear strand has allowed us to investigate the interactions between cells at a higher level of complexity. When, in the simplest case of a linear strand of three elements, the conductance between elements 2 and 3( G C2) is varied, this affects the success or failure of propagation between elements 1 and 2 (coupled by G C1) as well as the success or failure of propagation between elements 2 and 3. Several major features were illustrated. 1) When G C1 was only slightly greater than the coupling conductance required for successful propagation between a model cell and a real cell, addition of a third element of the strand either prevented conduction from element 1 to element 2 (when G C2 was high) or allowed conduction from element 1 to element 2 but not conduction from element 2 to element 3 (when G C2 was low). 2) For higher levels of G C1, there was an allowable "window" of values of G C2 for successful conduction from element 1 through to element 3. The size of this allowable window of G C2 values increased with increasing values of G C1, and this increase was produced by increases in the upper bound of G C2 values. 3) When the size of the central element of the strand was reduced, this facilitated conduction through the strand, increasing the range of the allowable window of G C2 values. The overall success or failure of conduction through a structure of cells that has a spatially inhomogeneous distribution of coupling conductances cannot be predicted simply by the average or the minimum value of coupling conductance but may depend on the actual spatial distribution of these conductances.