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Effect of tetrodotoxin on transmembrane potential of atrial muscle.

The effect of tetrodotoxin (5 x 10-8-10-6 g/ml) on the transmembrane potential was studied in the left atrial strip of rabbit. Tetrodotoxin (5 x 10-8-10-7 g/ml) produced an increase in the latent period, a decrease in rate of rise and a diminution in action potential magnitude with depressed overshoot. The magnitude of the resting potential showed little alteration. At a higher concentration (10-6 g/ml), the diminution in action potential magnitude became marked, and the resting potential decreased. The effect of tetrodotoxin on the transmembrane potential was greatly modified by the presence of manganese, suggesting the interaction between the two drugs. Above results may be interpreted on the basis of an inhibiting action of tetrodotoxin on the sodium-carrier system in rabbit atrial muscle.