Abstract
The human ether-a-go-go-related gene (hERG) encodes a channel that conducts the rapidly activating delayed rectifier K+ current (IKr), which is important for cardiac repolarization. Mutations in hERG reduce IKr and cause congenital long QT syndrome (LQTS). More frequently, common medications can reduce IKr and cause LQTS as a side effect. Protein trafficking abnormalities are responsible for most hERG mutation-related LQTS and are recently recognized as a mechanism for drug-induced LQTS. Whereas hERG trafficking has been studied in recombinant expression systems, there has been no reported study on cardiac IKr trafficking at the protein level. In the present study, we identified that IKr is present in cultured neonatal rat ventricular myocytes and can be robustly recorded using Cs+ as the charge carrier. We further discovered that 4,4′-(isopropylidenedithio)-bis-(2,6-di-t-butylphenol) (probucol), a cholesterol-lowering drug that induces LQTS, disrupted IKr trafficking and prolonged the cardiac action potential duration. Probucol did not directly block IKr. Probucol also disrupted hERG trafficking and did not block hERG channels expressed in human embryonic kidney 293 cells. We conclude that probucol induces LQTS by disrupting ether-a-go-go-related gene trafficking, and that primary culture of neonatal rat cardiomyocytes represents a useful system for studying native IKr trafficking.
Footnotes
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The project was supported by operating grants from the Canadian Institutes of Health Research and the Heart and Stroke Foundation of Manitoba to Shetuan Zhang, who is 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.107.120931.
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ABBREVIATIONS: hERG, human ether-a-go-go-related gene; IKr, cardiac rapidly activating delayed rectifier K+ current; LQTS, long QT syndrome; probucol, 4,4′-(isopropylidenedithio)-bis-(2,6-di-t-butylphenol); HEK, human embryonic kidney; PBS, phosphate-buffered saline; TBS, Tris-buffered saline; TBST, Tris-buffered saline/Tween 20; ERG, ether-a-go-go-related gene; siRNA, small inhibitory RNA; E-4031, 1-[2-(6-methyl-2-pyridyl)ethyl]-4-(methylsulfonyl-aminobenzoyl) piperidine; I-V, current-voltage; ER, endoplasmic reticulum; GFP, green fluorescent protein; HA, hemagglutinin.
- Received February 3, 2007.
- Accepted March 20, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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