EFFECTS OF ATROPINE, TETRODOTOXIN AND LIDOCAINE ON REBOUND EXCITATION OF GUINEA-PIG SMALL INTESTINE

¹ Department of Biology, Williams College, Williamstown, Massachusetts

The circular muscle of guinea-pig small intestine was mechnically and electrically inactive when equilibrated at 37°C in Krebs' solution. Transmural electrical stimulation was followed by poststimulus rebound contractions and associated action potentials. The duratin of the poststimulus response was progressively increased by increasing concentrations of atropine, procaine, tetrodotoxin and lidocaine. Procaine, tetrodotoxin and lidocaine increased the latent period of the poststimulus response, decreased the initial frequency of actioim potentials of the response and decreased the amplitude of the poststimulus cointraction. These same parameters of the poststimulus response were unaffected by atropine. Continuous discharge of action potentials in the circular muscle produced by high concentrations of atropine was inhibited by transmural electrical stimulation. This inhibition was not antagonized by guanethidine but was removed by procaine, tetrodotoxin and lidocaine.