Propagation Down a Chain of Excitable Cells by Electric Field Interactions in the Junctional Clefts: Effect of Variation in Extracellular Resistances, Including a "Sucrose Gap" Simulation

An electric field model for electrical transfer of excitation between contiguous excitable cells has been further developed by expanding the model to a chain of six cells, and examining the effect of changing the external resistances on propagation velocity. In this model, there is no requirement for low-resistance connections between the cells, and the major assumption is that the pre-and postjunctional membranes are ordinary excitable membranes. The electric field that develops in the narrow junctional cleft between contiguous cells during the rising phase of the action potential in the prejunctional membrane acts to depolarize the postjunctional membrane to threshold. Propagation occurred down the entire chain of cells at a constant velocity of about 17.1 cm/s. Raising the extracellular resistances (ROL and ROR) along the entire chain up to fourfold slowed propagation only slightly. However, when the radial cleft resistance (RJC) was varied concomitantly, then there was a marked slowing of propagation velocity, e.g., to 3.3 cm/s in 4.0 X resistance. There was an optimal RJC value for peak velocity. The lowering of ROL and ROR up to eightfold has almost no effect on velocity. Raising RJC, ROL, and ROR for the middle two cells, up to 3 times the normal value slowed propagation in the "sucrose-gap" region; raising the resistance to 4 times or higher blocked propagation. Hence, the electric field model allows successful transmission of excitation down a long chain of cells, not connected by low-resistance tunnels, at a constant velocity, and propagation velocity is dependent particularly on RJC.