The actions of 'selective' excitatory amino acid antagonists on the crustacean neuromuscular junction.

Intracellular recordings of neurally evoked excitatory junction potentials were made from the hermit crab neuromuscular junction and the effects of a series of putative antagonists, including the phosphonic amino acids, were examined for their effectiveness. The most potent antagonists were (+/-)2-amino-5-phosphonohexanoic acid and (+/-) 2-amino-5-phosphonovaleric acid while glutamate diethyl ester, DL-alpha-aminoadipate, 2-amino-7-phosphonoheptanoic acid and gamma-D-glutamylglycine were less effective. None of the compounds produced a change in membrane input resistance, but pyridine-2,5-dicarboxylic acid depolarized the muscle membrane and this probably accounted for its apparent antagonist properties. All the compounds readily and reversibly, but not competitively, antagonized the ionophoretic L-glutamate-induced depolarization. Since none of the compounds was capable of producing complete antagonism it is concluded that a more potent and competitive antagonist is required.