Functional coupling between metabotropic glutamate receptors and G proteins in rat brain membranes

Functional activation of GTP-binding (G) proteins coupled with metabotropic glutamate receptors was evaluated in rat brain membranes. L-Glutamate stimulated the high-affinity GTPase activity in cerebral cortical, hippocampal, and striatal membranes with a mean concentration eliciting a half-maximal response (EC50) of 4.8, 1.6, and 4.9 microM, respectively. The enzyme activity in cerebral cortical membranes was also stimulated by (2S, 1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) with a mean EC50 of 0.90 microM, but not by L-2-amino-4-phosphonobutyrate (L-AP4) up to 10 microM. This method opens up a strategy for investigation of functional coupling between Group II metabotropic glutamate receptors and G proteins in native brain membranes.