Abstract
The use of cocaine causes cardiac arrhythmias and sudden death. Blockade of the cardiac potassium channel human ether-á-go-go-related gene (hERG) has been implicated as a mechanism for the proarrhythmic action of cocaine. hERG encodes the pore-forming subunits of the rapidly activating delayed rectifier K+ channel (IKr), which is important for cardiac repolarization. Blockade of IKr/hERG represents a common mechanism for drug-induced long QT syndrome. The mechanisms for many common drugs to block the hERG channel are not well understood. We investigated the molecular determinants of hERG channels in cocaine-hERG interactions using site-targeted mutations and patch-clamp method. Wild-type and mutant hERG channels were heterologously expressed in human embryonic kidney 293 cells. We found that there was no correlation between inactivation gating and cocaine block of hERG channels. We also found that consistent with Thr-623, Tyr-652, and Phe-656 being critical for drug binding to hERG channels, mutations in these residues significantly reduced cocaine-induced block, and the hydrophobicity of the residues at position 656 dictated the cocaine sensitivity of the channel. Although the S620T mutation, which removed hERG inactivation, reduced cocaine block by 21-fold, the S620C mutation, which also completely removed hERG inactivation, did not affect the blocking potency of cocaine. Thus, Ser-620 is another pore helix residue whose mutation can interfere with cocaine binding independently of its effect on inactivation.
Footnotes
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This work was supported by a grant-in-aid from the Heart and Stroke Foundation of Manitoba and from Manitoba Health Research Council to S.Z., a recipient of the New Investigator Award from the Heart and Stroke Foundation of Canada.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.105.098103.
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ABBREVIATIONS: LQTS, long QT syndrome; IKr, cardiac rapidly activating delayed rectifier K+ current; hERG, human ether-á-go-go-related gene; MK-499, (+)-N-[1′-(6-cyano-1,2,3,4-tetrahydro-2(R)-naphthalenyl)-3,4-dihydro-4(R)-hydroxyspiro(2H-1-benzopyran-2,4′-piperidin)-6-yl]methanesulfonamide] monohydrochloride; EAG, ether-á-go-go; bEAG, bovine ether-á-go-go; WT, wild-type; HEK, human embryonic kidney; PCR, polymerase chain reaction; E-4031, 1-[2-(6-methyl-2-pyridyl)ethyl]-4-(methylsulfonyl-aminobenzoyl) piperidine; I-V, current-voltage.
- Received November 3, 2005.
- Accepted January 4, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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