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 mod el cell and a real cell. The inclusion of additional elements to make a lin ear 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 var ied, 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 b etween elements 2 and 3. Several major features were illustrated. 1)When G( C1) was only slightly greater than the coupling conductance required for su ccessful propagation between a model cell and a real cell, addition of a th ird element of the strand either prevented conduction from element 1 to ele ment 2 (when G(C2) was high) or allowed conduction from element 1 to elemen t 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 siz e 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 o f G(C2) values. 3) When the size of the central element of the strand was r educed, this facilitated conduction through the strand, increasing the rang e of the allowable window of G(C2) values. The overall success or failure o f conduction through a structure of cells that has a spatially inhomogeneou s distribution of coupling conductances cannot be predicted simply by the a verage or the minimum value of coupling conductance but may depend on the a ctual spatial distribution of these conductances.