pISSN 1226-4512 eISSN 2093-3827

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Korean J Physiol Pharmacol 2003; 7(2): 53-57

Published online April 30, 2003

Copyright © The Korean Journal of Physiology & Pharmacology.

Mechanism of Glutamate-induced [Ca2⁢]i Increase in Substantia Gelatinosa Neurons of Juvenile Rats

Sung Jun Jung, Jeong Sook Choi, Jiyeon Kwak1, Jun Kim1, Jong Whan Kim, and Sang Jeong Kim

Department of Physiology, College of Medicine, Kangwon National University, Chunchon; 1Department of Physiology, Seoul National University College of Medicine, Seoul, Korea

Abstract

The glutamate receptors (GluRs) are key receptors for modulatory synaptic events in the central nervous system. It has been reported that glutamate increases the intracellular Ca2⁢ concentration ([Ca2⁢]i) and induces cytotoxicity. In the present study, we investigated whether the glutamate-induced [Ca2⁢]i increase was associated with the activation of ionotropic (iGluR) and metabotropic GluRs (mGluR) in substantia gelatinosa neurons, using spinal cord slice of juvenile rats (10∼21 day). [Ca2⁢]i was measured using conventional imaging techniques, which was combined with whole-cell patch clamp recording by incorporating fura-2 in the patch pipette. At physiological concentration of extracellular Ca2⁢, the inward current and [Ca2⁢]i increase were induced by membrane depolarization and application of glutamate. Dose-response relationship with glutamate was observed in both Ca2⁢ signal and inward current. The glutamate-induced [Ca2⁢]i increase at holding potential of ⁣70 mV was blocked by CNQX, an AMPA receptor blocker, but not by AP-5, a NMDA receptor blocker. The glutamate-induced [Ca2⁢]i increase in Ca2⁢ free condition was not affected by iGluR blockers. A selective mGluR (group I) agonist, RS-3,5-dihydroxyphenylglycine (DHPG), induced [Ca2⁢]i increase at holding potential of ⁣70 mV in SG neurons. These findings suggest that the glutamate-induced [Ca2⁢]i increase is associated with AMPA-sensitive iGluR and group I mGluR in SG neurons of rats.

Keywords: Substantia gelatinosa neuron, Glutamate, Intracellular Ca2⁢, concentration, NMDA receptor, AMPA receptor, Metabotropic glutamate receptor