Modulation of the Purkinje-ventricular muscle junctional conduction by elevated potassium and hypoxia

Abstract

Action potential transmission in the canine ventricle normally occurs from the Purkinje (P) system into the ventricular muscle (VM) at specific P-VM junction sites. Transitional (T) cells are located between the Purkinje and the ventricular (V) cells at these P-VM junction sites. It has been shown that exposure to elevated [K+]0 in combination with hypoxia produces an increase in the P-VM conduction time. To examine this increase in P-VM conduction time, simultaneous measurements of the action potential upstrokes of T cells and the activation times of the local P and V cells at P-VM junctional sites were obtained from in vitro canine papillary muscles. The effects of elevated [K+]0 and hypoxia on conduction from P cells to T cells was then compared with the conduction from T cells to V cells to assess the relative contribution of each to the increase in the P-VM conduction time. We found that this intervention has approximately equal effects on the two sequential steps involved in P-VM conduction. We then analyzed the increased delay from T cells and V cells on the basis of three hypothetical mechanisms: 1) increased coupling resistance, 2) decreased V cell excitability, and 3) decreased cellular responsiveness of the T cells. Our results show that the effects of elevated [K+]0 and hypoxia on T-VM delay can be accounted for by a decreased responsiveness of the T cells without any significant electrical uncoupling between T and V cells or decrease in VM excitability.