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- Title
Coexistence of hERG current block and disruption of protein trafficking in ketoconazole-induced long QT syndrome.
- Authors
Takemasa, H.; Nagatomo, T.; Abe, H.; Kawakami, K.; Igarashi, T.; Tsurugi, T.; Kabashima, N.; Tamura, M.; Okazaki, M.; Delisle, B. P.; January, C. T.; Otsuji, Y.
- Abstract
<bold>Background and Purpose: </bold>Many drugs associated with acquired long QT syndrome (LQTS) directly block human ether-a-go-go-related gene (hERG) K(+) channels. Recently, disrupted trafficking of the hERG channel protein was proposed as a new mechanism underlying LQTS, but whether this defect coexists with the hERG current block remains unclear. This study investigated how ketoconazole, a direct hERG current inhibitor, affects the trafficking of hERG channel protein.<bold>Experimental Approach: </bold>Wild-type hERG and SCN5A/hNa(v) 1.5 Na(+) channels or the Y652A and F656C mutated forms of the hERG were stably expressed in HEK293 cells. The K(+) and Na(+) currents were recorded in these cells by using the whole-cell patch-clamp technique (23 degrees C). Protein trafficking of the hERG was evaluated by Western blot analysis and flow cytometry.<bold>Key Results: </bold>Ketoconazole directly blocked the hERG channel current and reduced the amount of hERG channel protein trafficked to the cell surface in a concentration-dependent manner. Current density of the hERG channels but not of the hNa(v) 1.5 channels was reduced after 48 h of incubation with ketoconazole, with preservation of the acute direct effect on hERG current. Mutations in drug-binding sites (F656C or Y652A) of the hERG channel significantly attenuated the hERG current blockade by ketoconazole, but did not affect the disruption of trafficking.<bold>Conclusions and Implications: </bold>Our findings indicate that ketoconazole might cause acquired LQTS via a direct inhibition of current through the hERG channel and by disrupting hERG protein trafficking within therapeutic concentrations. These findings should be considered when evaluating new drugs.
- Subjects
KETOCONAZOLE; ANTIFUNGAL agents; PHARMACOLOGY; CELL membranes; MEDICAL sciences; MUSCLE protein metabolism; BINDING sites; FLOW cytometry; RESEARCH; GENETIC mutation; WESTERN immunoblotting; TIME; BIOLOGICAL transport; RESEARCH methodology; LONG QT syndrome; MEDICAL cooperation; EVALUATION research; ELECTROPHYSIOLOGY; COMPARATIVE studies; DOSE-effect relationship in pharmacology; MEMBRANE transport proteins; CYTOLOGY; MEMBRANE proteins; CELL lines; CARRIER proteins; PHARMACODYNAMICS; CHEMICAL inhibitors
- Publication
British Journal of Pharmacology, 2008, Vol 153, Issue 3, p439
- ISSN
0007-1188
- Publication type
journal article
- DOI
10.1038/sj.bjp.0707537