Coupling of glutamatergic receptors to changes in intracellular Ca2+ in rat cerebellar granule cells in primary culture

Abstract

Changes in cytosolic free Ca2+ concentrations, [Ca2+]i, in response to glutamate and glutamate receptor agonists were measured in rat cerebellar granule cells grown on coverslips. The intracellular Ca2+ as measured with fura-2 increased by applying kainate, N-methyl-D-aspartate (NMDA), quisqualate, and (RS)-d-amino-3-hydroxy-5-methyl-4-isoxazole-propionic (AMPA). When the extracellular Mg2+ was removed, the effects of NMDA and the NMDA receptor agonist cis-(+-)-1-amino-1,3-cyclopentanedicarboxylic acid (cis-ACPD) on intracellular Ca2+ were augmented. Glycine potentiated the effects of NMDA and cis-ACPD if the membrane was depolarized by increasing the extracellular K+ concentration. The NMDA receptor antagonist DL-2-amino-5-phosphonopentanic acid (AP5) abolished and the antagonist 3-([+-]-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) greatly reduced the effect of NMDA in both the normal and the Mg-free media. The dose-response curves of NMDA and, to a lesser extent, of kainate were shifted to the left, and that of quisqualate became biphasic in the Mg-free medium. The increase in [Ca2+]i produced by high quisqualate concentrations in the Mg-free medium was totally abolished by AP5. The results suggest that Ca2+ influx in cerebellar granule cells occurs through both NMDA- and non-NMDA-coupled ion channels. A part of the quisqualate-induced rise in cytosolic Ca2+ seems to be linked to the activation of NMDA receptors.