title: Ca2+ entry via AMPA/KA receptors and excitotoxicity in cultured cerebellar Purkinje cells.
abstract: Initial studies of glutamate receptors activated by kainate (KA) found them to be Ca2+ impermeable. Activation of these receptors was thought to produce Ca2+ influx into neurons only indirectly by Na(+)-dependent depolarization. However, Ca2+ entry via AMPA/KA receptors has now been demonstrated in several neuronal types, including cerebellar Purkinje cells. We have investigated whether such Ca2+ influx is sufficient to induce excitotoxicity in cultures of cerebellar neurons enriched for Purkinje cells. Agonists at non-NMDA receptors induced Ca2+ influx in the majority of these cells, as measured by whole-cell voltage clamp and by fura-2 [Ca2+]i microfluorimetry. To assess excitotoxicity, neurons were exposed to agonists for 20 min and cell survival was evaluated by a fluorescence assay 24 hr later. KA (100 microM) reduced neuronal survival relative to controls to 43 +/- 3% when applied in Na(+)-containing solution and to 45 +/- 3% in Na(+)-free solution. This toxicity was blocked completely by CNQX but only slightly by 100 microM Cd2+ and 50 microM D-(-)-2-amino-5-phosphonovaleric acid. Both Purkinje neurons and non-Purkinje cell types present in the cultures were similarly vulnerable to toxic KA exposure, but the population marked by KA-induced Co2+ uptake was selectively diminished by the excitotoxicity. Na(+)-independent excitotoxicity could also be induced by domoate, AMPA, or glutamate. Compared to KA, NMDA was relatively ineffective in inducing cell death. Most of the KA-induced excitotoxicity could be blocked by removal of extracellular Ca2+ during the KA exposure and for a 5 min period thereafter. Furthermore, antagonists of the Ca(2+)-activated enzymes nitric oxide synthase and calpain significantly reduced the KA-induced cell death. These results show that non-NMDA receptor activation can cause excitotoxicity in cerebellar Purkinje neurons by mechanisms not involving Na+ influx, but rather depending on direct Ca2+ permeation and activation of Ca(2+)-dependent enzymatic processes.
authors.affiliation: Department of Neurology, University of Chicago, Illinois 60637.
authors.forename: J R
authors.initials: JR
authors.lastname: Brorson
authors.forename: P A
authors.initials: PA
authors.lastname: Manzolillo
authors.forename: R J
authors.initials: RJ
authors.lastname: Miller
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D007608:Kainic Acid / Q000494:pharmacology*; D011689:Purkinje Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D018091:Receptors, AMPA / Q000378:metabolism*; D018092:Kainic Acid Receptors / Q000378:metabolism*
chemical_list: D002118:Calcium; D005971:Glutamates; D018698:Glutamic Acid; D007608:Kainic Acid; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors