The membrane components of crustacean neuromuscular systems. I. Immunity of different electrogenic components to tetrodotoxin and saxitoxin

Axon spikes in crayfish and lobster neuromuscular preparations were blocked bytetrodotoxin or saxitoxin (concentration 10⁻⁹ to10⁻⁸ g/ml). Responses evoked in the excitatory synaptic membrane byionophoretically applied glutamate, or in the inhibitory by GABA were unaffected byconcentrations of the poisons up to 10⁻⁵ g/ml. These confirm otherfindings that the poisons do not affect electrically inexcitable membrane components.“Miniature” p.s.p.’s, which indicate local secretory activity inthe presynaptic terminals were unaffected by the poisons. Electrical stimuli applied tothe axon terminals elicited localized p.s.p.’s after spike electrogenesis of theaxons was blocked. Thus, persistence of secretory activity may be linked to persistence ofdepolarizing K activation in the axons. Spikes induced in the muscle fibers by procainewere not affected by the poisons. In correlation with other data this finding indicatesthat the depolarizing electrogenic element, which does not depend upon Na activation inthe normally gradedly responsive muscles, differs chemically from the Na activationcomponent which is present in the conductile membrane of various cells. Three othervarieties of electrically excitable response which are present in crayfish muscle fibers(hyperpolarizing Cl activation, depolarizing K inactivation, and K activation) were,likewise, immune to the toxin.