A series of 10 amino acid and 17 peptide analogs of L‐glutamate were tested for their ability to block the neurally‐evoked contractions of the retractor unguis muscle isolated from the grasshopper, Romalea microptera. The two most active amino acids other than L‐glutamate were L‐cysteine sulfinic acid and L‐cysteic acid. Like L‐glutamate, 3 × 10−3 M L‐cysteine sulfinic acid was able to block completely the indirect contractile response of the muscle and to elicit muscular contractions. During desensitization or reduction of the neurally‐elicited response, the excitatory postsynaptic potential (EPSP) and graded, electrically‐excited potential were almost completely abolished. Of the β‐substituted amino acids, the compounds with the sulfonyl or sulfinyl groups were more active than the compounds with the phosphonyl or phosphoryl groups. Projection drawings of molecular models of the β‐substituents indicated that the size of the β‐substituent was a critical factor for activity. L‐α‐Hydroxyglutaric acid (2 × 10−2M) induced erratic contractions which were considered the result of an action on the postsynaptic membrane and not limited to the subsynaptic areas. Of the 17 peptides tested at 10−2M, 14 reduced the neurally‐evoked contractions by 10% or more. L‐Glutamic acid decarboxylase (10−4 g/ml) and α‐bungarotoxin (2.5 × 10−5 g/ml) did not alter the neurallyevoked contractile response.
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience