Introduction

The Nav1.5 α-subunit, encoded by SCN5A, together with its associated regulatory and anchoring proteins, constitute a macromolecular complex underlying the cardiac Na⁺ current, I_Na, which is essential for the generation and transmission of the action potential. I_Na dysfunction causes life-threatening arrhythmias. Recently, we demonstrated that the Nav1.5 α subunits interact with each other. Here, we characterized a truncating SCN5A mutation, which was identified in a patient with a mixed clinical phenotype of sick sinus syndrome and atrial fibrillation.

Methods

Wild type (WT) and mutated Nav1.5 channels were transiently expressed in HEK293 cells and their effects studied by biochemical and patch clamp analysis.

Results

The R1860GfsX12 truncating mutation in the Nav1.5 C-terminus causes partial proteasomal degradation of the mutant channel. Nevertheless, some of the mutant channels reach the plasma membrane, as shown by cell surface biotinylation. Patch-clamp recording in cells expressing the mutant channels showed a marked reduction of I_Na density by 70% compared to cells expressing the WT channels, and impaired biophysical properties. Surprisingly, co-transfection of WT with R1860GfsX12 in a 1:1 ratio almost restored the WT I_Na. In addition, co-expression of WT and R1860GfsX12 channels increased cell surface and total expression of the mutant channels, suggesting that WT channels allow mutant proteins to escape proteasomal degradation. Moreover, co-immunoprecipitation studies clearly showed that R1860GfsX12 channels still interact with WT channels. Altogether, our results suggest that WT could interact with mutant α-subunits, thus preventing their proteasomal degradation, and that both channels traffic together to the plasma membrane.

Conclusion

Multiple mechanisms underlie functional consequences of SCN5A mutations, which could explain why some mutations are responsible for ventricular arrhythmias, while others, such as R1860GfsX12, cause a milder atrial phenotype.

 

عنوان المؤتمر

Heart rhythm 2013

دولة المؤتمر

الولايات المتحدة الأمريكية

تاريخ المؤتمر

8 مايو، 2013 - 11 مايو، 2013

راعي المؤتمر

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معلومات إضافية

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