Complex interplay between glutamate receptors and intracellular Ca2+ stores during ischaemia in rat spinal cord white matter

摘要

Electrophysiological recordings of propagated compound action potentials (CAPs) and axonal Ca2+ measurements using confocal microscopy were used to study the interplay between AMPA receptors and intracellullar Ca2+ stores in rat spinal dorsal columns subjected to in vitro combined oxygen and glucose deprivation (OGD). Removal of Ca2+ or Na+ from the perfusate was protective after 30 but not 60 min of OGD. TTX was ineffective with either exposure, consistent with its modest effect on ischaemic depolarization. In contrast, AMPA antagonists were very protective, even after 60 min of OGD where 0Ca2+ + EGTA perfusate was ineffective. Similarly, blocking ryanodine receptor-mediated Ca2+ mobilization from internal stores (0Ca2+ + nimodipine or 0Ca2+ + ryanodine), or inositol 1,4,5-trisphosphate (IP3)-dependent Ca2+ release (block of group 1 metabotropic glutamate receptors with 1-aminoindan-1,5-dicarboxylic acid, inhibition of phospholipase C with U73122 or IP3 receptor block with 2APB; each in 0Ca2+) were each very protective, with the combination resulting in virtually complete functional recovery after 1 h OGD (97 ± 32% CAP recovery versus 4 ± 6% in artificial cerebrospinal fluid). AMPA induced a rise in Ca2+ concentration in normoxic axons, which was greatly reduced by blocking ryanodine receptors. Our data therefore suggest a novel and surprisingly complex interplay between AMPA receptors and Ca2+ mobilization from intracellular Ca2+ stores. We propose that AMPA receptors may not only allow Ca2+ influx from the extracellular space, but may also significantly influence Ca2+ release from intra-axonal Ca2+ stores. In dorsal column axons, AMPA receptor-dependent mechanisms appear to exert a greater influence than voltage-gated Na+ channels on functional outcome following OGD.