The molecular basis of high-affinity binding of the antiarrhythmic compound vernakalant (RSD1235) to Kv1.5 channels.

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Eldstrom J, Wang Z, Xu H, Pourrier M, Ezrin A, Gibson K, Fedida D

The molecular basis of high-affinity binding of the antiarrhythmic compound vernakalant (RSD1235) to Kv1.5 channels.

Mol Pharmacol. 2007 Dec;72(6):1522-34. Epub 2007 Sep 14.

PubMed ID

17872968 [ View in PubMed

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Abstract

Vernakalant (RSD1235) is an investigational drug recently shown to convert atrial fibrillation rapidly and safely in patients (J Am Coll Cardiol 44:2355-2361, 2004). Here, the molecular mechanisms of interaction of vernakalant with the inner pore of the Kv1.5 channel are compared with those of the class IC agent flecainide. Initial experiments showed that vernakalant blocks activated channels and vacates the inner vestibule as the channel closes, and thus mutations were made, targeting residues at the base of the selectivity filter and in S6, by drawing on studies of other Kv1.5-selective blocking agents. Block by vernakalant or flecainide of Kv1.5 wild type and mutants was assessed by whole-cell patch-clamp experiments in transiently transfected human embryonic kidney 293 cells. The mutational scan identified several highly conserved amino acids, Thr479, Thr480, Ile502, Val505, and Val508, as important residues for affecting block by both compounds. In general, mutations in S6 increased the IC50 for block by vernakalant; I502A caused an extremely local 25-fold decrease in potency. Specific changes in the voltage-dependence of block with I502A supported the crucial role of this position. A homology model of the pore region of Kv1.5 predicted that, of these residues, only Thr479, Thr480, Val505, and Val508 are potentially accessible for direct interaction, and that mutation at additional sites studied may therefore affect block through allosteric mechanisms. For some of the mutations, the direction of changes in IC50 were opposite for vernakalant and flecainide, highlighting differences in the forces that drive drug-channel interactions.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Vernakalant	Potassium voltage-gated channel subfamily A member 5	Protein	Humans	Yes	Blocker	Details