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CARDIOVASCULAR

Identification of I_Kr and Its Trafficking Disruption Induced by Probucol in Cultured Neonatal Rat Cardiomyocytes

Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada

The human ether-a-go-go-related gene (hERG) encodes a channel that conducts the rapidly activating delayed rectifier K⁺ current (I_Kr), which is important for cardiac repolarization. Mutations in hERG reduce I_Kr and cause congenital long QT syndrome (LQTS). More frequently, common medications can reduce I_Kr 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 I_Kr trafficking at the protein level. In the present study, we identified that I_Kr 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 I_Kr trafficking and prolonged the cardiac action potential duration. Probucol did not directly block I_Kr. 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 I_Kr trafficking.

Address correspondence to: Shetuan Zhang, Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre and Department of Physiology, Faculty of Medicine, University of Manitoba, 351 Tache Avenue, Winnipeg, MB, Canada R2H 2A6. E-mail: szhang{at}sbrc.ca