Excitation of intestinal muscle by atropine, tetrodotoxin, and xylocaine.

WOOD, J. D. Excitation of intestinal muscle by atropine, tetrodotoxin, and Xylocaine. Am. J. Physiol. 222(l): li8-125. 1972.-The circular muscle layer of cat jejunum was mechanically and electrically quiescent when equilibrated in Tyrode solution at 37 C. Atropine, procaine, tetrodotoxin, and Xylocaine produced action potentials and a large increase in the amplitude of contractions in the circular muscle. High concentrations of Xylocaine suppressed circular muscle activity. The excitatory response to atropine and Xylocaine did not occur after 7 days of storage at 5 C; suppression by high concentrations of Xylocaine was not affected by storage. Barium chloride produced excitation after 7 days of storage. Circular muscle activity produced by atropine was inhibited by transmural electrical stimulation. This inhibition was not antagonized by guanethidine, but was abolished by procaine, tetrodotoxin, and Xvlocaine. Conducted responses to mechanical stimulation were . more easily elicited and were propagated over greater distances after blockade of enteric neurons. The results indicate that myogenie activity of the circular muscle is continuously inhibited by spontaneously active inhibitory pathways within the enteric nervous system. The mechanism of the excitatory action of the drugs appears to not be directly on the muscle, but to involve removal of inhibition from the muscle by interrupting nervous transmission within the pathways. Myogenic mechanisms trigger action potentials and associated contractions when inhibition is removed.