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 coverlips. The intracellular Ca²⁺ as measured with fura‐2increased 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‐AMONO‐5‐phosphonopentanoic 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 recptors.