Modulation of the Purkinje-ventricular muscle junctional conduction by elevated potassium and hypoxia.
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.
Tan
R C
RC
Department of Pediatrics, Emory University, Atlanta, Georgia 30322.
Ramza
B M
BM
Joyner
R W
RW
D000200:Action Potentials; D000818:Animals; D004285:Dogs; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D008297:Male; D009200:Myocardial Contraction; D010100:Oxygen / Q000502:physiology*; D010210:Papillary Muscles / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D016276:Ventricular Function
D011188:Potassium; D010100:Oxygen