Nitric oxide applications prior and simultaneous to potentially excitotoxic NMDA-evoked calcium transients: cell death or survival.
Nitric oxide (NO) is a molecule that plays a prominent role in neurotoxic as well as neuroprotective pathways. Here, we investigated the effects of NO on potentially excitotoxic glutamate-induced intracellular calcium ([Ca2+]i) dynamics. Our hypothesis was that pre- and coexposure to NO in conjunction with glutamate receptor stimulation modulates [Ca2+]i responses differentially. [Ca2+]i transients, assessed by the fluorescent cytosolic Ca2+ indicator dye fluo-4, were elicited in mouse striatal neurons by consecutive NMDA applications (200 microM for 100 s each). Subgroups of neuronal cultures were additionally exposed to a NO donor (S-nitroso-N-acetyl-d,l-penicillamine, SNAP, 50-500 microM), either by pre- (for 6 h prior to NMDA) or cotreatment (for 30 min during NMDA). Pretreatment with NO led to dramatically decreased NMDA-evoked [Ca2+]i rises in comparison to controls (NMDA alone). Annexin V/propidium iodide staining showed consistently that NO pretreatment is protective against NMDA-induced cell death. In contrast, NO/NMDA cotreatment caused a potentiation of [Ca2+]i rises, whereby the duration of [Ca2+]i transients following NMDA application was prolonged and remained at an increased plateau level. Simultaneous application of the mitochondrial permeability transition pore (mtPTP) blocker cyclosporin A (2 microM) during the NO/NMDA cotreatment prevented the deregulation of [Ca2+]i. The observed [Ca2+]i deregulation was accompanied by a decrease in the mitochondrial membrane potential as indicated by tetramethylrhodamine methylester (TMRM) fluorescence. These findings suggest that NO can act in a protective way due to preconditioning or can have a possibly detrimental impact in case of acute release. They provide a possible explanation for the ambivalence of NO in neurodegenerative processes where glutamate receptor stimulation and mitochondrial [Ca2+]i sequestration are causally involved.
Schröter
Aileen
A
Institute for Medical Neurobiology, Otto-von-Guericke University, Leipziger Str. 44, D-39120 Magdeburg, Germany.
Andrabi
Shaida A
SA
Wolf
Gerald
G
Horn
Thomas F W
TF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology*; D051379:Mice; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D016166:Free Radical Scavengers; D009569:Nitric Oxide; D016202:N-Methylaspartate; D016572:Cyclosporine; D002118:Calcium