Pharmacological Properties of Hindgut Visceral Muscle of the Cockroach, Periplaneta americana L.(Orthoptera:Blattidae) : I.The Effect of Glutamate Agonists, Glutamate Antagonists and Several Ion Channel Blockers

Effects of agonists for glutamate receptors, L-glutamic acid, quisqualic acid, kainic acid, domoic acid and ibotenic acid on mechanical responses of the hindgut isolated from American cockroaches were examined by measuring isotonic contractions with a mechano-electroc transducer. Ibotenic acid exerted an inhibitory effect, and all others had excitatory actions. L-glutamic acid and quisqualic acid produced phasic-tonic contractions, while kainic acid and domoic acid produced phasic contractions only. Verapamil at 5×10-6 M abolished spontaneous peristaltic movements of the isolated hindgut and suppressed the agonist-induced contractile responses by 50% (at 10-5-10-4 M agonist concentrations). Ibotenic acid at 5×10-5 M completely inhibited the peristaltic movements of the hindgut, and picrotoxinin, a chloride-channel blocker, prevented ibotenate from acting. Responses to L-glutamic acid and quisqualic acid were effectively blocked by glutamate dimethyl ester, but the resonses to kainic acid and domoic acid were more susceptible to blockage by 2-amino-4-phosphonobutyric acid, γ-D-glutamylglycine and D-α-aminoadipic acid. These results sults suggest that there may be three distinct types of glutamate receptors on the hindgut muscle of American cockroaches : the quisqualate-activated receptor (type I) is preferentially antagonized by glutamate dimethyl ester, the kainate/domoinate-activated receptor (type II) is more effectively blocked by 2-amino-4-phosphonobutyric acid and γ-D-glutamylglycine than by glutamate dimethyl ester, and the ibotenate-activated receptor (type III) is sensitive to chloride-channel blocker, picrotoxinin.