Ramasamy Lakshminarayanan, Sperelakis Nicholas
Dept. of Molecular & Cellular Physiology, University of Cincinnati College of Medicine Cincinnati, OH 45267-0576, USA.
Theor Biol Med Model. 2007 Sep 14;4:36. doi: 10.1186/1742-4682-4-36.
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 (lambda).
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 (theta(ov)). 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), theta(ov) was slightly slowed with lengthening of the chain. Increasing the number of gj-channels produced an increase in theta(ov) 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 (DeltaV(m)) 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 (lambda) increasing at higher numbers of gj-channels. The effect of increasing the number of gj-channels on increasing lambda was relatively small compared to the larger effect on theta(ov). theta(ov) became very non-physiological at 300 gj-channels or higher.
Thus, when there were only 0, 1, or 10 gj-channels, theta(ov) increased with increase in chain length, whereas at 100 gj-channels or higher, theta(ov) did not increase with chain length. When there were only 0, 10, or 30 gj-channels, there was a very sharp decrease in DeltaV(m) 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 theta(ov).
先前已在短单链心肌细胞和二维心肌细胞片层中研究了模拟动作电位（AP）的传播情况。本研究旨在检测不同长度、不同数量缝隙连接（g-j）通道的长单链细胞中的传播情况，并将传播速度与电缆特性（如长度常数（lambda））进行比较。
如前所述，使用PSpice程序进行模拟。当电场（EF）机制占主导（0、1和10个g-j通道）时，链长度越长，整体速度（theta(ov)）越快。对此现象似乎没有简单的解释。相比之下，当局部电路电流机制占主导（100个g-j通道或更多）时，theta(ov)随着链的延长而略有减慢。增加g-j通道数量会使theta(ov)增加，并使发放顺序变得更加均匀。在更长的链长度和更多的g-j通道数量时，末端效应更明显。当没有或只有很少的g-j通道（即0、10或30个）时，与注入电流的细胞（#51）相邻的两个细胞（#50和#52）中的电压变化（DeltaV(m)）几乎为零；也就是说，相邻细胞之间的电压存在急剧的不连续。当有许多g-j通道（例如300、1000、3000个）时，注入细胞两侧的电压呈指数衰减，在更多的g-j通道数量时，长度常数（lambda）增加。与对theta(ov)的较大影响相比，增加g-j通道数量对增加lambda的影响相对较小。在300个g-j通道或更高时，theta(ov)变得非常不符合生理情况。
因此，当只有0、1或10个g-j通道时，theta(ov)随着链长度的增加而增加，而在100个g-j通道或更高时，theta(ov)不随链长度增加。当只有0、10或30个g-j通道时，注入细胞两侧相邻的两个细胞中的DeltaV(m)急剧下降，而在300、1000或3000个g-j通道时，电压沿链的长度呈指数衰减。与对theta(ov)的较大影响相比，增加g-j通道数量对电流传播的影响相对较小。
