The sulphydryl inhibitors N-ethyl maleimide (NEM), iodoacetic acid (IAA), p-chloromercuribenzoic acid (PCMB), and mersalyl at concentrations in the millimolar range blocked the neurally evoked mechanical response of an isolated nerve-muscle preparation from the grasshopper, Romalea microptera, and also blocked the contractions evoked by external application of l-glutamic acid, the suspected excitatory neurotransmitter. Blockade caused by PCMB could be reversed completely by post-perfusion with dithiothreitol (DTT); however, that caused by mersalyl was irreversible. Protection could be achieved by prior mixture of inhibitors with equimolar concentrations of the thiols, l-cysteine or reduced glutathione. The alkylating agents NEM and IAA also reduced the retractor unguis contracture caused by depolarization with high K+ saline, whereas the organomercurials PCMB and mersalyl did not. The primary site of action appears to be the post-synaptic membrane. These findings indicate significant differences from the response of the eel electroplax preparation and suggest a functional rôle for free sulphydryl groups rather than disulphide linkages in this insect excitatory neuromuscular junction.
ASJC Scopus subject areas
- Insect Science