Nitric oxide enhances MPP +-induced hydroxyl radical generation via depolarization activated nitric oxide synthase in rat striatum

Abstract

We examined the effect of N G-nitro- l-arginine methyl ester ( l-NAME), a nitric oxide synthase (NOS) inhibitor, on extracellular potassium ion concentration ([K +] o)-enhanced hydroxyl radical ( ·OH) generation due to 1-methyl-4-phenylpyridinium ion (MPP +) was examined in the rat striatum. Rats were anesthetized, and sodium salicylate in Ringer’s solution (0.5 nmol/μl per min) was infused through a microdialysis probe to detect the generation of ·OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Induction of KCl (20, 70 and 140 mM) increased MPP +-induced ·OH formation trapped as 2,3-dihydroxybenzoic acid (DHBA) in a concentration dependent manner. However, the application of l-NAME (5 mg/kg i.v.) abolished the [K +] o depolarization-induced ·OH formation with MPP +. Dopamine (DA; 10 μM) also increased the levels of DHBA due to MPP +. However, the effect of DA after application of l-NAME did not change the levels of DHBA. On the other hand, the application of allopurinol (20 mg/kg i.v., 30 min prior to study), a xanthine oxidase (XO) inhibitor was abolished the both [K +] o- and DA-induced ·OH generation. Moreover, when iron(II) was administered to MPP + then [K +] o (70 mM)-pretreated animals, a marked increase in the level of DHBA. However, when corresponding experiments were performed with l-NAME-pretreated animals, the same results were obtained. Therefore, NOS activation may be no relation to Fenton-type reaction via [K +] o depolarization-induced ·OH generation. The present results suggest that [K +] o-induced depolarization augmented MPP +-induced ·OH formation by enhancing NO synthesis.