Ca2+-dependent and -independent mechanisms of ischaemia-evoked release of [3H]-dopamine from rat striatal slices.

1. Ischaemia was induced by 5 min of deprivation of glucose and an additional 5 min of deprivation of glucose and oxygen from Mg(2+)-free artificial cerebrospinal fluid in vitro. 2. During the ischaemic period, 11 +/- 1.5% of the total [3H]-dopamine ([3H]-DA) was released into the incubation medium. 3. Ischaemia-evoked release of [3H]-DA from striatal slices was attenuated by tetrodotoxin (TTX), MgSO4, dizocilpine, ketamine, 6,7-dinitroquinoxaline-2,3-dione (DNQX) or carbetapentane. 4. Release of [3H]-DA was attenuated by verapamil, omega-conotoxin GVIA and dantrolene. 5. Nomifensin inhibited the ischaemia-induced release of [3H]-DA. 6. Omission of Ca(2+) from incubation media potentiated ischaemia-evoked [3H]-DA release. The inhibitory effect of nomifensin was potentiated in Ca(2+)-free incubation media. 7. These results suggest that ischaemia induces release of [3H]-DA by dual mechanisms; one is Ca(2+)-dependent exocytosis and the other is reversal of transporter.