title: Modulation of the Ca++-evoked release of [3H]dopamine from striatal synaptosomes by dopamine (D2) agonists and antagonists.
abstract: Release of [3H]dopamine ([3H]DA) from striatal synaptosomes is evoked most commonly by elevating potassium levels in the presence of calcium. However, it has been difficult to show that DA agonists or antagonists can modify K+-evoked release of [3H]DA. DA. In this study [3H]DA release evoked by exposure of synaptosomes (isolated and superfused previously with 0.0 mM Ca++ and 0.1 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid) to 1.25 mM Ca++ can be modulated by the DA (D2) agonists apomorphine, pergolide and quinpirole and antagonists l-sulpiride and domperidone. The release was evoked under low potassium (6 mM or less) concentrations and the potassium concentration in the superfusion medium was not elevated before or during Ca++ exposure. Analysis of the superfusates obtained during Ca++ exposure revealed that approximately 80% of the tritium released was [3H]DA. The ability of DA (D2) agonists to inhibit the Ca++-evoked release from synaptosomes superfused with 9 mM K+ was greatly reduced. Therefore, prolonged depolarization may block DA (D2) regulation of [3H]DA release from synaptosomes. The Ca++-evoked release of [3H]DA was reduced greatly when 1 microM tetrodotoxin was present indicating sodium channels play a role in triggering the processes involved in Ca++-evoked [3H]DA release.
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D003342:Corpus Striatum / Q000166:cytology*; D004294:Domperidone / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D004873:Ergolines / Q000494:pharmacology; D010479:Pergolide / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D019257:Quinpirole; D051381:Rats; D013469:Sulpiride / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D004873:Ergolines; D015102:3,4-Dihydroxyphenylacetic Acid; D019257:Quinpirole; D010479:Pergolide; D013779:Tetrodotoxin; D004294:Domperidone; D013469:Sulpiride; D001058:Apomorphine; D011188:Potassium; D002118:Calcium; D004298:Dopamine