Effects of halothane on impulse propagation in Purkinje fibers and at Purkinje-muscle junctions: relationship of Vmax to conduction velocity.
Alterations in Purkinje-to-muscle conduction may play a role in the development of cardiac arrhythmias. We compared the effects of halothane on impulse propagation in Purkinje fibers with its effects on impulse propagation across the Purkinje-muscle (P-M) junction. In canine Purkinje fibers, halothane (3%) significantly depressed conduction (P less than 0.05). Exposure to halothane altered conduction velocity (theta) in a manner predicted by cable theory; a significant correlation was noted between depression of Vmax and depression of the square of conduction velocity (theta 2) in Purkinje fibers exposed to 3% halothane (n = 11, r = 0.78, P less than 0.01). Halothane (3%) significantly slowed impulse propagation across the P-M junction (P less than 0.05). Vmax and the square of apparent P-M conduction velocity were not significantly correlated (n = 7, r = 0.34, P = 0.45). The data demonstrate that alteration of active membrane properties can account for halothane's slowing of conduction in Purkinje fibers but not for its slowing of conduction across the P-M junction. The data also suggest that a reduction in cell-to-cell coupling may contribute to depression of Purkinje-to-muscle conduction by halothane.
Freeman
L C
LC
Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Ohio State University, Columbus.
Muir
W W
WW
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003864:Depression, Chemical; D004285:Dogs; D006221:Halothane / Q000494:pharmacology*; D066298:In Vitro Techniques; D010210:Papillary Muscles / Q000187:drug effects* / Q000502:physiology; D011690:Purkinje Fibers / Q000187:drug effects* / Q000502:physiology
D006221:Halothane