Endothelin downregulates the glutamate transporter GLAST in cAMP-differentiated astrocytes in vitro.
Endothelin (ET) is a putative pathogenetic mediator associated with brain trauma and ischemia. Because a link between neuronal damage after these injuries and glial Na(+)-dependent L-glutamate transporter activity has been suggested, we investigated the effect of ET on the glutamate clearance ability of astrocytes. Dibutyryl cyclic adenosine monophosphate (dBcAMP), which is widely used to induce differentiation of cultured astrocytes, markedly increased [(3)H]glutamate transport activity in a concentration- and time-dependent manner. In the presence of ET, however, dBcAMP decreased the glutamate uptake. This effect was efficiently prevented by an antagonist of ET(B) receptor, but not of ET(A) receptor. ET per se was virtually ineffective. Eadie-Hofstee analysis demonstrated that dBcAMP increased the V(max) value of glutamate uptake activity by 43.4% in the absence of ET, but decreased it by 41.4% in the presence of ET, without apparent changes in the K(m) value. Accordingly, Western blot analysis indicated that the change in transport activity correlated closely with that in expression level of the glial glutamate transporter GLAST. These results may represent the mechanisms by which ET aggravates trauma- and ischemia-elicited neuronal damage.
Matsuura
Sigeru
S
Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan.
Ikegaya
Yuji
Y
Yamada
Maki K
MK
Nishiyama
Nobuyoshi
N
Matsuki
Norio
N
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D027322:Amino Acid Transport System X-AG / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001930:Brain Injuries / Q000378:metabolism / Q000503:physiopathology; D003994:Bucladesine / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000378:metabolism* / Q000494:pharmacology; D005904:Glial Fibrillary Acidic Protein; D018698:Glutamic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D007150:Immunohistochemistry; D009410:Nerve Degeneration / Q000378:metabolism / Q000503:physiopathology; D051381:Rats; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000378:metabolism
D027322:Amino Acid Transport System X-AG; D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D005904:Glial Fibrillary Acidic Protein; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D018698:Glutamic Acid; D003994:Bucladesine