POTENTIATING AND DEPRESSANT EFFECTS OF METABOTROPIC GLUTAMATE-RECEPTOR AGONISTS ON HIGH-VOLTAGE-ACTIVATED CALCIUM CURRENTS IN CULTURED RETINAL GANGLION NEURONS FROM POSTNATAL MICE

This study was aimed at clarifying the role of metabotropic glutamate receptors (mGluRs) in the regulation of intracellular Ca2+ concentrati on ([Ca2+](i)) in postnatal mouse retinal ganglion neurons (RGNs). RGN s were maintained for 1-2 weeks in vitro by adding brain-derived neuro trophic factor (BDNF) and basic fibroblast growth factor (bFGF) to the culture medium. In order to select these cells for electrophysiologic al measurements, RGNs were vitally labelled with an antibody against T hy-1.2. Voltage-activated Ca2+ currents [I-Ca(V)] were recorded with p atch electrodes in the whole-cell configuration. It was found that rac emic +/-1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD) or it s active enantiomer 1S,3R-ACPD rapidly and reversibly either enhanced or depressed I-Ca(V). Quisqualate (QA), L-2-amino-4-phosphonobutyrate (L-AP4) and the endogenous transmitter glutamate induced similar effec ts when ionotropic glutamate receptors were blocked with D-2-amino-5-p hosphonovalerate (D-APV) and 6,7-dinitroquinoxaline-2,3-dione (DNQX). omega-Conotoxin GVIA (omega-CgTx GVIA), but not nifedipine prevented m odulation of I-Ca(V) by mGluR agonists. The depression of I-Ca(V) by t -ACPD was irreversible when cells were dialysed with guanosine-5'-O-(3 -thiotriphosphate) (GTP[gamma-S]). Ratio measurements of fura-2 fluore scence in Thy-1+ cells showed that neither t-ACPD, QA nor L-AP4 affect ed [Ca2+](i) by liberation of Ca2+ from intracellular stores. Our resu lts suggest that cultured RGNs express mGluRs. These receptors cannot induce Ca2+ release from intracellular stores but regulate [Ca2+]i by a fast and reversible, G-protein-mediated action on a subpopulation of voltage-activated Ca2+ channels.