Effects of bromohomoibotenate on metabotropic glutamate receptors.

(S)-Bromohomoibotenic acid [(S)-BrHIbo] stereoselectively antagonized glutamate-stimulated phosphoinositide (PI) hydrolysis in baby hamster kidney (BHK) cells expressing mGluR1a in a competitive manner with an IC50 of 250 microM. However, (S)-BrHIbo did not inhibit (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD]-induced PI hydrolysis in rat hippocampal slices (S)- or (R)-BrHIbo did not show any effects on forskolin-stimulated cAMP-formation in BHK cells expressing mGluR2 or mGluR4 but did displace [3H]2-amino-4-phosphonobutyrate ([3H]AP4) binding from rat corticalmembranes with high affinities (IC50 = 1.0 microM and 1.1 microM, respectively). These data suggest that (S)-BrHIbo may interest with multiple PI-coupled glutamate receptors, however, at concentrations that are several fold higher than for displacement of [3H]AP4 binding from rat cortical membranes.