electrophysiologic effects of halothane and quinidine on canine purkinje fibers evidence for a synergistic interaction the authors studied possible interactions between halothane and quinidine on the action potentials of canine purkinje fibers superfused with tyrodes solution using standard microelectrode techniques and a physiologic pacing rate 2 hz halothane in concentrations from 05 to 2 decreased the action potential duration to 50 repolarization adp50 total adp apd100 in contrast increased after 1 and 2 halothane resting membrane potential rmp and action potential amplitude apamp increased after 05 halothane but returned to control with higher halothane levels conduction time ct increased at each halothane level pacing at faster 3 hz or slower 1 hz rates did not markedly alter the effects of halothane quinidine 1 x 105m decreased the phase o upstroke vmax and prolonged apd100 and ct when halothane was added rmp and apamp decreased vmax decreased further and apd100 and ct were markedly prolonged this resulted in conduction block or inexcitability especially at faster pacing rates 3 hz synergistic interactions between halothane and quinidine were found on rmp apamp apd100 and ct effects on vmax apd50 and action potential duration to 90 repolarization apd90 were additive it is concluded that quinidine and halothane act synergistically to decrease action potential amplitude lower rmp and prolong conduction severe depression of conduction often progressed to conduction block or inexcitability when halothane 2 was administered during superfusion with therapeutic concentrations of quinidine