Potassium and Hypoxia

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'], 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+J0 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. (Circulation 1989;79:1100-1105)