Vol. 56, Issue 6, 1298-1308, December 1999

Modulation of the K⁺ Channels Encoded by the Human Ether-a-Gogo-Related Gene-1 (hERG1) by Nitric Oxide

Maurizio Taglialatela, Anna Pannaccione, Silvana Iossa, Pasqualina Castaldo, and Lucio Annunziato

Section of Pharmacology, Department of Neuroscience, School of Medicine, University of Naples Federico II, Naples, Italy

The inhibition of nitric oxide synthase by N-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 in Xenopus 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-nitroso N-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 on hERG1 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 hERG1 K⁺ 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 on hERG1 outward K⁺ currents via an interaction with radical oxygen species either generated under resting conditions or triggered by Fe/Asc.