Tetrodotoxin and Manganese Ions: Effects on Electrical Activity and Tension in Taenia Coli of Guinea Pig

Abstract

Tetrodotoxin, at concentrations up to 5 × 10 -6 gram per milliliter, has no effect on the spontaneous discharge in the smooth muscle of taenia coli. However, the spontaneous discharge is abolished by Mn ++ at a concentration of 0.5 millimole per liter. The contraction induced by immersing the muscle in isotonic KCl solution is also suppressed in the presence of Mn ++ . Because Mn ++ is a specific suppressor of the spike induced by Ca ++ and tetrodotoxin is an inhibitor of the spike induced by Na + , we suggest that Ca ++ is a charge carrier in the production of spike potential in the smooth muscle and that the entry of Ca ++ through the membrane acts as a trigger for the contraction of smooth muscle.