Hypoosmotic swelling increases protein tyrosine nitration in cultured rat astrocytes.
Astrocyte swelling is observed in different types of brain injury. We studied a potential contribution of swelling to protein tyrosine nitration (PTN) by using cultured rat astrocytes exposed to hypoosmotic (205 mosmol/L) medium. Hypoosmolarity (2 h) increases total PTN by about 2-fold in 2 h. The hypoosmotic PTN is significantly inhibited by the NMDA receptor antagonist MK-801, the nitric oxide synthase (NOS) inhibitor L-NMMA, the extracellular Ca2+ chelator EGTA and the calmodulin antagonist W13, suggesting the involvement of NMDA receptor activation, influx of extracellular Ca2+ and Ca2+/calmodulin-dependent NO synthesis. Further, superoxide dismutase plus catalase and uric acid strongly inhibit hypoosmotic PTN, suggesting the involvement of the toxic metabolite peroxynitrite (ONOO-) as a nitrating agent. Hypoosmotic astrocyte swelling rapidly stimulates generation of reactive oxygen intermediates; this process is prevented by MK-801 and EGTA. In addition, MK-801 inhibits the hypoosmotic elevation of [Ca2+]i. The findings support the view that astrocyte swelling as induced, for example, by toxins relevant for hepatic encephalopathy is sufficient to produce oxidative stress and PTN and thus contributes to altered astroglial and neuronal function.
Schliess
Freimut
F
Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany. freimut.schliess@uni-duesseldorf.de
Foster
Natalie
N
Görg
Boris
B
Reinehr
Roland
R
Häussinger
Dieter
D
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D001929:Brain Edema / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002147:Calmodulin / Q000378:metabolism; D048429:Cell Size / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006501:Hepatic Encephalopathy / Q000378:metabolism; D022124:Hyperammonemia / Q000378:metabolism; D007038:Hypotonic Solutions / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis; D009994:Osmolar Concentration; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D030421:Peroxynitrous Acid / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism*
D002147:Calmodulin; D002614:Chelating Agents; D018691:Excitatory Amino Acid Antagonists; D007038:Hypotonic Solutions; D009419:Nerve Tissue Proteins; D009566:Nitrates; D011506:Proteins; D017382:Reactive Oxygen Species; D016194:Receptors, N-Methyl-D-Aspartate; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D014443:Tyrosine