Independence of AP propagation velocity to transjunctional voltage dependence of gap junctional coupling

Gap junctions are protein structures that form transmembrane channels between adjacent cells, thereby allowing the direct passage of ions and small molecules. They play an important role in the physiological functioning of the individual cells, and also the tissue. Experimental studies have reported a variety of gap junction subtypes, with differences in their biophysical properties, such as their unitary conductances and sensitivity to transjunctional voltage. Our study aims at computationally exploring the effect of these differences towards the spread of action potentials in syncytial tissues. Results from our simulations suggest that the propagation velocity of action potentials is independent of the transjunctional voltage dependence of the gap junction subtype. The propagation velocity was found to be constant across all subtypes tested, when the maximal conductances were set equal. This was verified using action potentials of widely varying time courses. We attribute this trend to the much slower gating kinetics of gap junctions in comparison to the time course of action potentials, and more specifically the short period where a significant transjunctional voltage is maintained.