Nitric oxide blocks hKv1.5 channels by S-nitrosylation and by a cyclic GMP-dependent mechanism

Objective: This study was undertaken to analyze whether nitric oxide (NO) modulates the human potassium channel hKv1.5, which generates the ultrarapid delayed rectifier current (I-Kur) that determines the height and duration of atrial action potentials. Methods: Currents were recorded using the whole-cell patch-clamp in Ltk(-) cells expressing hKv1.5 channels. Results: The NO donors (+/-)-S-Nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprusside, a NO solution, and L-Arginine inhibited hKv1.5 currents in a concentration-dependent manner. The NO concentration in the cell chamber was monitored using a sensor, and the IC50 for NO-induced hKv1.5 block was 340 +/- 70 nM. SNAP also inhibited the I-Kur recorded in mouse ventricular myocytes. The NO effects were partially mediated by the activation of the soluble guanylate cyclase (sGC)/cGMP/cGMP-dependent protein kinase (PKG) pathway. The biotin-switch assay demonstrated the presence of S-nitrosylated cysteines (Cys) on the hKv1.5 protein in SNAP-treated cells. Molecular modeling of hKv1.5 channel structure suggests that S-nitrosylation of Cys331 (segment 2, S2) and Cys346 (S2) would be stabilized by hydrogen bridge bonds with Ile262 (S1) and Arg342 (S2), respectively. Conclusions: NO inhibits the hKv1.5 current by a cGMP-dependent mechanism and by the S-nitrosylation of the hKv1.5 protein, an effect that contributes to shaping the human atrial action potentials. (c) 2006 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.