Further structure activity studies on the excitatory amino acid receptors of the crustacean neuromuscular junction.

Intracellular recordings of the membrane potential and evoked excitatory junction potentials were made from the opener muscle in the walking leg of the Hermit crab ( Eupagurus bernhardus ). A variety of amino acid analogues including cis and trans 1-amino-1,3- dicarboxycyclopentane were tested for agonist activity and their potencies were compared with L-glutamate. Quisqualic acid was the most powerful excitant whereas N-methyl-DL-aspartic acid and ibotenic acid were the least active. Threshold concentrations of L-glutamate and quisqualic acid potentiated the ionophoretic L-glutamate potential and the excitatory junction potentials without affecting membrane input resistance. The results are discussed in terms of the structure-activity relationship of the crustacean excitatory receptor compared to other vertebrate and invertebrate nervous systems.