Abstract
The inhibition of nitric oxide synthase byN-nitro-l-arginine methyl ester (0.03–3 mM) dose-dependently reduced nitric oxide (NO⋅) levels and enhanced the outward currents carried by human ether-a-gogo-related gene-1 (hERG1) K+ channels expressed inXenopus laevis oocytes, whereas the increase in NO⋅ levels achieved by exposure to l-arginine (0.03–10 mM) inhibited these currents. Furthermore, four NO⋅donors belonging to such different chemical classes as sodium nitroprusside (1–1000 μM), 3-morpholino-sydnonimine (100–1000 μM), (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (NOC-18; 1–300 μM), and S-nitrosoN-acetylpenicillamine (1–300 μM) dose-dependently inhibited hERG1 outward K+ currents. By contrast, the NO⋅ donor NOC-18 (0.3 mM) did not affect other cloned K+ channels such as rat neuroblastoma-glioma K+ channel 2, rat delayed rectifier K+ channel 1, bovine ether-a-gogo gene, rat ether-a-gogo-related gene-2, and rat ether-a-gogo-related gene-3. The inhibitory effect of NO⋅ donors on hERG1 K+ channels was prevented by the NO⋅ scavengers 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide and hemoglobin. The membrane permeable analog of cGMP, 8-bromo-cGMP (1 mM), failed to reproduce the inhibitory action of NO⋅ donors onhERG1 outward currents; furthermore, the specific inhibitor of the NO⋅-dependent guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (50 μM), neither interfered with outward hERG1K+ currents nor prevented their inhibition by 0.3 mM NOC-18. Both l-arginine (10 mM) and NOC-18 (0.3 mM) counteracted the stimulatory effect on hERG1 outward currents induced by the radical oxygen species-generating system FeSO4 (25 μM)/ascorbic acid (50 μM; Fe/Asc). Finally,l-arginine (10 mM) and NOC-18 (0.3 mM) inhibited both basal and Fe/Asc (0.1 mM/0.2 mM)-stimulated lipid peroxidation in X. laevis oocytes. Collectively, the present results suggest that NO⋅, both endogenously produced and pharmacologically delivered, may exert in a cGMP-independent way an inhibitory effect onhERG1 outward K+ currents via an interaction with radical oxygen species either generated under resting conditions or triggered by Fe/Asc.
Footnotes
- Received July 26, 1999.
- Accepted September 8, 1999.
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Send reprint requests to: Dr. Maurizio Taglialatela, Section of Pharmacology, Department of Neuroscience, School of Medicine, Via. S. Pansini 5, 80131 Naples, Italy. E-mail:mtaglial{at}unina.it
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The study was supported by Telethon Grant 1058 (to M.T.); National Research Council (CNR) Grants 97.04512.CT04, 97.01230.PF49, and 98.03149.CT04 (to M.T.) and CNR Grants 95.02857.CT04, 98.01048.CT04, and 98.00062.PF31 (PS Biotecnologie 5%) (to L.A.); MURST 60% and 40% (to L.A.); and grants from the Regione Campania (P.O.P. and Legge 41) (to L.A.).
- The American Society for Pharmacology and Experimental Therapeutics
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