Gamma-glutamyl peptides and related amino acids in rat hippocampus in vitro: effect of depolarization and gamma-glutamyl transpeptidase inhibition.
The concentrations of gamma-glutamylglutamate, gamma-glutamylglutamine, gamma-glutamylcysteine, glutamate, aspartate, glutamine, cyst(e)ine and glutathione (including disulfides) were determined by HPLC analysis of both the tissue and the surrounding medium of incubated rat hippocampal slices. High potassium concentrations (50 mM; 2 x 4 min) increased the medium concentration of gamma-glutamylglutamate (maximal net efflux 0.07 +/- 0.06 pmol/mg protein/min; n = 8 +/- SD) with a relative time delay compared to the increase in glutamate (maximal net efflux 264 +/- 88 pmol/mg protein/min). Release of gamma-glutamylcysteine, the glutathione precursor, demonstrated an immediate response and gradually approached prestimulus levels (maximal net efflux 0.36 +/- 0.13 pmol/mg protein/min). Addition of acivicin (0.2 mM), a gamma-glutamyl transpeptidase (EC 2.3.2.2.) blocker, during preincubation for 45 min reduced the tissue concentrations (pmol/mg protein) of gamma-glutamylglutamate (19.4 +/- 8.2 (control) vs. 5.8 +/- 3.6 (+ acivicin)), gamma-glutamylglutamine (40.3 +/- 6.7 vs. 25.7 +/- 4.2 pmol/mg protein), glutamine (9.9 +/- 2.0 vs. 4.6 +/- 1.2 nmol/mg protein) and cysteine (1.0 +/- 0.2 vs. 0.56 +/- 0.18 nmol/mg protein). Incubation with acivicin (0.2 mM) reduced the net efflux of gamma-glutamylglutamine (0.79 +/- 0.19 vs. 0.21 +/- 0.07 pmol/mg protein/min) whereas that of the glutathione was increased (4.7 +/- 1.0 vs. 20 +/- 3 pmol/mg protein/min). The medium concentrations of glutamate in both low and high potassium were unaffected by acivicin, while the high potassium induced increase in gamma-glutamylglutamate was blocked. The results demonstrate differential efflux patterns of gamma-glutamyl dipeptides from brain slices and show that in vitro the activity of gamma-glutamyl transpeptidase regulates extracellular concentrations of glutathione, gamma-glutamylglutamine and gamma-glutamylglutamate.
Li
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Institute of Anatomy and Cell Biology, University of Göteborg, Sweden.
Orwar
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Revesjö
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Sandberg
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D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D004151:Dipeptides / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000031:analogs & derivatives* / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D007555:Isoxazoles / Q000494:pharmacology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors*
D000596:Amino Acids; D004151:Dipeptides; D004791:Enzyme Inhibitors; D005971:Glutamates; D007555:Isoxazoles; D005973:Glutamine; C082810:gamma-glutamylglutamate; C047442:gamma-glutamylglutamine; D001224:Aspartic Acid; D018698:Glutamic Acid; D005723:gamma-Glutamyltransferase; D005978:Glutathione; D003545:Cysteine; C017341:gamma-glutamylcysteine; C006303:acivicin