Okadaic acid and cyclosporin A modulate [(3)H]GABA release from rat brain synaptosomes.
Rat brain synaptosomes were used to investigate the effect of okadaic acid, an inhibitor of protein phosphatase 1 and 2A, and cyclosporin A, an inhibitor of protein phosphatase 2B (calcineurin), on [(3)H]GABA release. Release of [(3)H]GABA was evoked by 4-aminopyridine in the presence of calcium and by alpha-latrotoxin in the presence and absence of calcium. Pretreatment of synaptosomes with 1 microM okadaic acid reduced [(3)H]GABA release evoked by 4-aminopyridine by about 40%. The effect of alpha-latrotoxin on [(3)H]GABA release was stimulated by okadaic acid. This stimulation was equal in both media. The stimulating effect of 4-aminopyridine and alpha-latrotoxin on [(3)H]GABA release was activated when synaptosomes were pretreated with cyclosporin A. Activation of 4-aminopyridine-evoked [(3)H]GABA release was observed at 1 microM cyclosporin A, but the toxin effect was enhanced only when concentration of cyclosporin A was increased to 10 microM. The level of cyclosporin A activation depended on alpha-latrotoxin concentrations used - a higher stimulating effect of cyclosporin A was observed with lower toxin concentration. These results suggest that in calcium medium 4-aminopyridine- and alpha-latrotoxin-evoked [(3)H]GABA release was realized by different mechanisms.
Storchak
L G
LG
Department of Neurochemistry, Palladin Institute of Biochemistry, National Academy of Science of Ukraine, St. Leontovich 9, Kiev 01601, Ukraine.
Kravchuk
M V
MV
Himmelreich
N H
NH
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology*; D019319:Okadaic Acid / Q000494:pharmacology*; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D013111:Spider Venoms; D014316:Tritium; D019319:Okadaic Acid; D005680:gamma-Aminobutyric Acid; C020763:alpha-latrotoxin; D016572:Cyclosporine; D015761:4-Aminopyridine; D002118:Calcium