Both 3,4-dihydroxyphenylalanine and dopamine releases are regulated by Ca2+-induced Ca2+ releasing system in rat striatum.

To clarify the striatal Ca2+-dependent monoaminergic exocytosis mechanisms, this study determined the effects of the Ca2+-induced Ca2+ releasing system (CICR), containing inositol-trisphosphate-receptor (IP3R) and ryanodine-receptor (RyR), on striatal releases of dopamine and its precursor, 3,4-dihydroxyphenylalanine (DOPA), using microdialysis. The basal dopamine release is regulated by IP3R but not by RyR, whereas basal DOPA release does not require CICR. The K+-evoked releases of DOPA and dopamine were enhanced by IP3R agonist, whereas RyR agonist reduced it. Additionally, inhibition of dopamine release induced by RyR hyperactivation was prevented by inhibition of L-type voltage-sensitive Ca2+-channel activity. These present results suggest that CICR-associated regulation of striatal releases of DOPA and dopamine is restrictive during the resting stage, whereas CICRs play an important role as a reserve mechanism of exocytosis of striatal DOPA and dopamine during the hyperexcitable stage.