Characterization of metabotropic glutamate receptor-stimulated phosphoinositide hydrolysis in rat cultured cerebellar granule cells.

1. The pharmacology of excitatory amino acid (EAA)-stimulated phosphoinositide (PI) hydrolysis, monitored via [3H]-inositol monophosphate accumulation, was investigated in primary cultures of rat cerebellar granule cells. 2. EAA-stimulated PI hydrolysis peaked after 4-5 days in vitro and subsequently declined. 3. The agonist order of potency was found to be (EC50): L-quisqualic acid (Quis) (2 microM) >> L-glutamate (50 microM) > (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid ((1S,3R)-ACPD) (102 microM). L-Glutamate (Emax = 873% of basal activity) elicited the largest stimulation of PI hydrolysis, whereas Quis (Emax = 603%) and (1S,3R)-ACPD (Emax = 306%) produced somewhat lower stimulations. 4. Several phenylglycine derivatives were found to be active in inhibiting 2 microM Quis-stimulated PI hydrolysis, in order of potency (IC50): (S)-4-carboxy-3-hydroxyphenylglycine (41 microM) > or = (S)-4-carboxyphenylglycine (51 microM) >> (+)-alpha-methyl-4-carboxyphenylglycine (243 microM). 5. Cultured cerebellar granule cells of the rat appear to have Group I mGluR pharmacology similar to that reported for cloned mGluR1 and provide an ideal system for investigating novel mGluR1 ligands in a native environment.