Turnover and release of GABA in rat cortical slices: effect of a GABA-T inhibitor, gabaculine.
The turnover and release of endogenous and labeled GABA were followed in rat cortical slices after incubation with [3H]GABA. High performance liquid chromatography was used to measure endogenous GABA and to separate [3H]GABA from its metabolites. During superfusion with 3 mM K+ the slices rapidly lost their [3H]GABA content while maintaining constant GABA levels. Exposure to 50 mM K+ for 25 min caused an initial rapid rise in the release of both endogenous and [3H]GABA followed by a more rapid decline in the release of the latter. The specific activity of released GABA was two to four times higher than that in the slices. Depolarization lead to a net synthesis of GABA. The GABA -T inhibitor, gabaculine, (5 micrometers) in vitro arrested the metabolism of [3H]GABA and rapidly doubled the GABA content but did not significantly increase the high K+ evoked release of endogenous GABA. In vivo pretreatment with 0.5 mM/kg gabaculine quadrupled GABA content and increased both the spontaneous and evoked release of endogenous GABA but while its Ca2+ -dependent release increased by 50%, the Ca2+ -independent release was enhanced sevenfold. This large Ca2+ -independent release of GABA is likely to have different functional significance from the normal Ca2+ -dependent release.
D000612:4-Aminobutyrate Transaminase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D046508:Culture Techniques; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology*; D009457:Neuroglia / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D003509:Cyclohexanecarboxylic Acids; D014316:Tritium; C012987:gabaculine; D005680:gamma-Aminobutyric Acid; D000612:4-Aminobutyrate Transaminase; D011188:Potassium; D002118:Calcium