Signaling pathways in the nitric oxide and iron-induced dopamine release in the striatum of freely moving rats: Role of extracellular Ca²⁺ and L-type Ca²⁺ channels

We showed previously that exogenous iron potentiated nitric oxide (NO) donor-induced release of striatal dopamine (DA) in freely moving rats, using microdialysis. In this study, the increase in dialysate DA induced by intrastriatal infusion of the NO-donor 3-morpholinosydnonimine (SIN-1, 1.0 mM for 180 min) was scarcely affected by Ca²⁺ omission. N-methyl-d-glucamine dithiocarbamate (MGD) is a thiol compound whose NO trapping activity is potentiated by iron(II). Intrastriatal co-infusion of MGD either alone or associated with iron(II), however, potentiated SIN-1-induced increases in dialysate DA. In contrast, co-infusion of the NO trapper 4-(carboxyphenyl)-4, 4,5,5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO) significantly attenuated the increase in dialysate DA induced by SIN-1 (5.0 mM for 180 min). SIN-1+MGD+iron(II)-induced increases in dialysate DA were inhibited by Ca ²⁺ omission or co-infusion of either deferoxamine or the L-type (Ca_v 1.1-1.3) Ca²⁺ channel inhibitor nifedipine; in contrast, the increase was scarcely affected by co-infusion of the N-type (Ca_v 2.2) Ca²⁺ channel inhibitor ω-conotoxin GVIA. These results demonstrate that exogenous NO-induced release of striatal DA is independent on extracellular Ca²⁺; however, in presence of the NO trapper MGD, NO may preferentially react with either endogenous or exogenous iron to form a complex which releases striatal DA with an extracellular Ca ²⁺-dependent and nifedipine-sensitive mechanism.