2 NOVEL TYPES OF L-GLUTAMATE RECEPTORS WITH AFFINITIES FOR NMDA AND L-CYSTEINE IN THE OLFACTORY ORGAN OF THE CARIBBEAN SPINY LOBSTER PANULIRUS-ARGUS

A subset of olfactory receptor neurons of the Caribbean spiny lobster Panulirus argus possesses receptors for L-glutamate that can mediate b oth excitatory and inhibitory responses (P.C. Daniel, M.F. Burgess, C. D. Derby, Responses of olfactory receptor neurons in the spiny lobster to binary mixtures are predictable using a non-competitive model that incorporates excitatory and inhibitory transduction pathways, J. Comp . Physiol. A 178 (1992) 523-536). In this study, we have used biochemi cal and electrophysiological techniques to understand the role of thes e receptors in olfactory transduction, and to compare these olfactory glutamate receptors with peripheral and central L-glutamate receptors in other animals. Using a radioligand-binding assay with a membrane-ri ch preparation from the dendrites of olfactory receptor neurons, we ha ve identified two types of binding sites for L-glutamate. Both sites s howed rapid, reversible, and saturable association with radiolabeled L -glutamate, and their K-d values (1 nM and 3 mu M) are effective in ph ysiological studies of glutamate-sensitive olfactory neurons, suggesti ng these binding sites are receptors involved in olfactory transductio n. Both sites were completely inhibited by high concentrations of NMDA and L-cysteine, and only partially inhibited by other L-glutamate ana logs and odorants. Electrophysiological recordings from L-glutamate-be st olfactory receptor neurons showed that NMDA and L-cysteine are both partial agonists and antagonists of glutamate receptors. Together, th ese results suggest the olfactory L-glutamate receptors of spiny lobst ers are novel types of L-glutamate receptors that are functionally imp ortant in mediating olfactory responses. (C) 1997 Elsevier Science B.V .