Résumé :
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Communication n° 259 Introduction : A number of inherited ion channelopathies are characterized by a trafficking defect of the channel protein toward the plasma membrane, resulting in a loss-of-function. A few studies have shown that the mutant channels may be rescued by drugs that bind to the channel protein, likely acting as pharmacological chaperones. The mechanisms as well as the molecular requisites for such an effect remain elusive. Objective : To define the molecular requisites in class I antiarrhythmic drugs to increase plasma membrane expression of voltage-gated sodium channels. Methods : Human skeletal muscle sodium channels (hNav1.4) were stably expressed in HEK293 cells. The cells were incubated for 24 or 48 hours with the drugs and sodium channel density was assayed with the whole-cell patch clamp technique by measuring the maximum sodium current normalized by the cell membrane capacitance (INa in pA/pF). Results : The cloned HEK293 cells presented a quite constant sodium channel density, being 308.9 Æ 12.5 pA/pF (n=116). Incubation with 30 µM mexiletine had no effect on INa but, with 100-300 µM mexiletine, INa was increased by 88-46 % after 24 hours and 66-103% after 48 hours. Incubation with flecainide increased INa by 95-143 % after 24 hours and by 90-72 % after 48 hours with 100-300 µM flecainide. However, flecainide was more potent than mexiletine, since 30 µM flecainide increased significantly INa by 91 % after 48 hours incubation, but not after 24 hours. The membrane-impermeant tetrodotoxin reversibly blocks sodium current by ~95 % when applied acutely at 1 µM. However, INa was not modified after 24-48 hours incubation with 1 µM tetrodotoxin. Discussion : The results show that incubation with class I antiarrhythmic drugs increase sodium channel density, most probably through a chaperone-like effect. Conclusion : This study provides the basis for a detailed investigation of the mechanisms and molecular requisites needed to obtain chaperone-like compounds able to rescue mutant channels in inherited sodium channelopathies including the hypokalemic periodic paralysis type 2 and the Brugada syndrome, both characterized by a loss-of-function of the sodium channel. (supported by Italian MIUR-FIRB RBNE01XMP4 and Telethon-Italy #GGP04140)
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