Pertussis toxin blocks presynaptic glutamate receptors--a novel 'glutamateB' receptor in the lobster neuromuscular synapse.

Topical application of L-glutamate to the neuromuscular synapse of the lobster walking leg induced K+-dependent hyperpolarization in the presynaptic membrane. This presynaptic glutamate potential (PGP) was insensitive to Joro spider toxin (JSTX), a spider toxin which specifically blocks the postsynaptic glutamate receptor, but was blocked by pertussis toxin island activating protein (IAP) in a dose-dependent manner. IAP had little effect on the resting conductance channels in pre- and postsynaptic membranes. GTP gamma S, a hydrolysis-resistant analogue of GTP, reduced the PGP supporting the involvement of G-protein in generation of K+ activation. The results suggest that a new type of glutamate receptor exists in the presynaptic membrane in the crustacean neuromuscular synapse.