Effect of Ca<SUP>2&#8290;</SUP>-channel Blockers on Norepinephrine Release in the Rat Hippocampal Slice and Synaptosome

Effect of Ca<SUP>2&#8290;</SUP>-channel Blockers on Norepinephrine Release in the Rat Hippocampal Slice and Synaptosome

The aim of this study was to investigate the role of Ca<SUP>2&#8290;</SUP>-channel blockers in norepinephrine (NE) release from rat hippocampus. Slices and synaptosomes were incubated with [<SUP>3</SUP>H]-NE and the releases of the labelled products were evoked by 25 mM KCl stimulation. Nifedipine, diltiazem, nicardipine, flunarizine and pimozide did not affect the evoked and basal release of NE in the slice. But, diltiazem, nicardipine and flunarizine decreased the evoked NE release with a dose-related manner without any change of the basal release from synaptosomes. Also, a large dose of pimozide produced modest decrement of NE release. ω-conotoxin (CTx) GVIA decreased the evoked NE release in a dose-dependent manner without changing the basal release. And ω-CTxMVIIC decreased the evoked NE release in the synaoptosomes without any effect in the slice, but the effect of decrement was far less than that of ω-CTxGVIA. In interaction experiments with ω-CTxGVIA, ω-CTxMVIIC slightly potentiated the effect of ω-CTxGVIA on NE release in the slice and synaptosomal preparations. These results suggest that the NE release in the rat hippocampus is mediated mainly by N-type Ca<SUP>2&#8290;</SUP>-channels, and that other types such as L-, T- and/or P/Q-type Ca<SUP>2&#8290;</SUP>-channels could also be participate in this process.