| Summary: | A plasma membrane rich (PMR) preparation derived from olfactory rosettes of Atlantic salmon (Salmo salar) was used to study the binding sites for the amino acid glutamate. The combined binding study and Northern blot analyses suggest that a Glu receptor is present in the salmon olfactory system with properties similar to the metabotropic Glu receptors (mGluRs) found in mammalian brain. These properties include inhibition of olfactory Glu binding by mGluR ligands, apparent coupling of Glu binding to phospholipase C (PLC) and the presence of RNAs that hybridize with cDNAs of mGluRs. These three levels of evidence suggest that the salmon olfactory system includes a subtype of the mGluR family. The expression of the family of G$\sb{\rm q}$ proteins in salmon brain was investigated. Western blot analyses demonstrate that a salmon homologue of the G$\sb{\rm q}$ family exists in salmon brain, suggesting that the previously detected G$\sb{\rm q}$ homologue in olfactory tissue might not be olfactory specific. Alternatively, there might be two or more G$\sb{\rm q}$ homologues present in salmon, one of which is olfactory specific. A PMR preparation from salmon olfactory epithelium was used to define the binding site for inositol tetrakisphosphate (IP$\sb4$). The combined binding and analog inhibition studies strongly demonstrate abundant binding sites for IP$\sb4$ in the plasma membrane of salmon olfactory rosettes. This IP$\sb4$ binding site may be responsible for Ca$\sp{2+}$ influx and therefore may trigger cell depolarization and the firing of action potentials. Full length cDNAs were cloned from a salmon olfactory cDNA library which are only expressed in olfactory tissue. The specific expression of these cDNAs suggest that they may play certain physiological roles in olfactory reception or transduction. A revised and expanded working model for salmon olfactory glutamate reception and transduction is proposed and includes specific signal transduction components found to be expressed and active in the salmon olfactory system.
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