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Effect of brevetoxin-B on the neuromuscular transmission of the mouse diaphragm.

The effects of brevetoxin-B, a polyether toxin isolated from Gymnodinium breve Davis, on neuromuscular transmission were studied on the mouse hemidiaphragm using general pharmacological and electrophysiological methods. Brevetoxin-B initially induced spontaneous muscle twitching followed by complete paralysis of the indirectly elicited twitch tension of the mouse diaphragm. The directly elicited muscle twitch tension was not affected and the compound action potential of the phrenic nerve could still be recorded when neuromuscular transmission was completely blocked by the toxin. Brevetoxin-B initially increased, but then decreased, the antidromic activity of the phrenic nerve. Brevetoxin-B increased the frequency of miniature endplate potentials (MEPP), while it decreased the muscle membrane potential. Application of tetrodotoxin (TTX) completely abolished the increase in MEPP frequency and the depolarization of the muscle membrane potential. The results suggested that brevetoxin-B may affect the sodium channels in the nerve terminal and muscle membrane.