Effects of ammonia on glutamate transporter (GLAST) protein and mRNA in cultured rat cortical astrocytes.
Ammonia is a neurotoxic substance which accumulates in brain in liver failure and it has been suggested that ammonia plays a key role in contributing to the astrocytic dysfunction characteristic of hepatic encephalopathy. In particular, the effects of ammonia may be responsible for the reduced astrocytic uptake of neuronally-released glutamate and high extracellular glutamate levels consistently seen in experimental models of hepatic encephalopathy. To further address this issue, [(3)H]-D-aspartate uptake was examined in primary rat cortical astrocyte cultures exposed to 5 mM ammonium chloride for a period of 7 days. In addition, reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot studies were performed to examine the mRNA and protein expression respectively of the glutamate transporter GLAST in ammonia-treated cells. Studies revealed a 57% (p<0.05) decrease in [(3)H]-D-aspartate uptake and a concomitant significant decrease in GLAST transporter protein (43%, p<0.05) and mRNA (32%, p<0.05) expression. The reduced capacity of astrocytes to reuptake glutamate following ammonia exposure may result in compromised neuron-astrocyte trafficking of glutamate and could thus contribute to the pathogenesis of the cerebral dysfunction characteristic of hyperammonemic syndromes such as hepatic encephalopathy.
Chan
H
H
Neuroscience Research Unit, CHUM (Campus Saint-Luc), Montreal, Canada.
Hazell
A S
AS
Desjardins
P
P
Butterworth
R F
RF
D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001253:Astrocytes / Q000378:metabolism*; D015153:Blotting, Western; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D012333:RNA, Messenger; D000643:Ammonium Chloride; D001224:Aspartic Acid