The effect of cellular discontinuities on the transient subthreshold response of a one-dimensional cardiac model.
Previous studies have examined the influence of the gap-junction discontinuity on the steady-state response of a cardiac cable to electrical defibrillation. It is important to understand when steady-state conditions may be assumed. For this reason, the transient, subthreshold behavior of a discontinuous cardiac cable is examined in this study. The behavior of the cable reflects two characteristics: 1) the continuous nature of the entire cable and 2) the isolated behavior of individual cells imposed by the junction discontinuity. The results show two effective time constants of activation: a large time constant corresponding to the time constant of a continuous cable of equivalent length, and a small time constant reflecting the rapid activation of an isolated cell. The rapid activation establishes a voltage gradient across each cell of the cable with one end of the cell hyperpolarized and the opposite end depolarized. This pattern of hyperpolarization and depolarization reaches a maximum value in approximately 3 microseconds and may play an important role in the mechanism of defibrillation.
Cartee
L A
LA
Department of Biomedical Engineering, School of Engineering, Duke University, Durham, NC 27706.
Plonsey
R
R
D007365:Intercellular Junctions / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008955:Models, Cardiovascular