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

Tetrodotoxin, at concentrations up to 5 x 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 intervening Ca++ through the membrane acts as a trigger for the contraction of smooth muscle.

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