Effects of quinidine and diphenylhydantoin on membrane resistance in smooth muscle

The effects of quinidine and diphenylhydantoin on the membrane electrical resistance of guinea-pig taenia coli have been studied by means of the double sucrose gap tachnique. At concentrations ranging from 2 to 7.10-minus 5 quinidine induces an evident dose-related increase of membrane resistance, as indicated by the increase of the electrotonic potential. These effects are unaffected by tetrodotoxin (10(-6)) and in the presence of various changes of ionic environment (replacement of Na by Li, increase of K or Ca or Mg concentrations). Only a concomitant rise of both K and Ca (or Mg) can prevent the effects of quinidine on membrane resistance. The rate of repetitive discharge under sustained electrical depolarization is not affected by quinidine, at concentrations increasing membrane resistance. The experiments with diphenylhydantoin showed that this drug is practically ineffective on membrane resistance, but induces a decrease of the rate of repetitive discharge under sustained depolarization.