|
Abstract : |
Abstract Background Propagation of simulated action potentials (APs) was previously studied in short single chains and in two-dimensional sheets of myocardial cells 123. The present study was undertaken to examine propagation in a long single chain of cells of various lengths, and with varying numbers of gap-junction (g-j) channels, and to compare propagation velocity with the cable properties such as the length constant (λ). Methods and Results Simulations were carried out using the PSpice program as previously described. When the electric field (EF) mechanism was dominant (0, 1, and 10 gj-channels), the longer the chain length, the faster the overall velocity (θov). There seems to be no simple explanation for this phenomenon. In contrast, when the local-circuit current mechanism was dominant (100 gj-channels or more), θov was slightly slowed with lengthening of the chain. Increasing the number of gj-channels produced an increase in θov and caused the firing order to become more uniform. The end-effect was more pronounced at longer chain lengths and at greater number of gj-channels. When there were no or only few gj-channels (namely, 0, 10, or 30), the voltage change (ΔVm) in the two contiguous cells (#50 & #52) to the cell injected with current (#51) was nearly zero, i.e., there was a sharp discontinuity in voltage between the adjacent cells. When there were many gj-channels (e.g., 300, 1000, 3000), there was an exponential decay of voltage on either side of the injected cell, with the length constant (λ) increasing at higher numbers of gj-channels. The effect of increasing the number of gj-channels on increasing λ was relatively small compared to the larger effect on θov. θov became very non-physiological at 300 gj-channels or higher. Conclusion Thus, when there were only 0, 1, or 10 gj-channels, θov increased with increase in chain length, whereas at 100 gj-channels or higher, θov did not increase with chain length. When there were only 0, 10, or 30 gj-channels, there was a very sharp decrease in ΔVm in the two contiguous cells on either side of the injected cell, whereas at 300, 1000, or 3000 gj-channels, the voltage decay was exponential along the length of the chain. The effect of increasing the number of gj-channels on spread of current was relatively small compared to the large effect on θov., |
