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Okadaic acid and cyclosporin A modulate [(3)H]GABA release from rat brain synaptosomes
Authors:Storchak L G  Kravchuk M V  Himmelreich N H
Institution:Department of Neurochemistry, Palladin Institute of Biochemistry, National Academy of Science of Ukraine, St. Leontovich 9, Kiev 01601, Ukraine.
Abstract: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.
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