Possible heterogeneity of metabotropic glutamate receptors induced in Xenopus oocytes by rat brain mRNA.

Pharmacological properties of metabotropic glutamate receptors were studied in Xenopus oocytes injected with rat brain mRNA. trans-1-Amino-cyclopentyl-1,3-dicarboxylic acid (t-ACPD), a conformationally restricted analog of glutamate, induced oscillatory inward currents in mRNA-injected oocytes. These t-ACPD responses showed several characteristics identical to those of the other metabotropic responses including the metabotropic glutamate responses stimulated by quisqualate. D,L-2-Amino-3-phophonopropionate (D,L-AP3) effectively suppressed the t-ACPD and ibotenate responses. However, quisqualate responses were not affected substantially by D,L-AP3. These findings suggest that the metabotropic glutamate receptors in the oocytes may be classified into at least two subtypes according to their pharmacological properties: one preferentially activated by quisqualate and insensitive to AP3, and the other activated by t-ACPD and ibotenate and antagonized by AP3.