K(+)-evoked dopamine release depends on a cytosolic Ca2+ pool regulated by N-type Ca2+ channels.

Membrane depolarization evoked by 25-40 mM K+ elicited an immediate increase of somatic and neuritic [Ca2+]i in cultured dopaminergic neurons as measured by digital fluorescence microscope imaging. The rise of neuritic [Ca2+]i was inhibited by N-type but not L-type Ca2+ channel blockers, while the rise of somatic [Ca2+]i was prevented by both L- and N-type Ca2+ channel blockers. Similarly, depolarization-induced [3H]dopamine release was selectively attenuated by N-type Ca2+ channel blockers. The present results suggest that [3H]dopamine release from mesencephalic neuronal cell cultures relates to a Ca(2+)-dependent mechanism regulated by N-type channels located in the vicinity of the exocytotic sites within neuritic processes.