Trafficking and localisation to the plasma membrane of Na 1.5 promoted by the β2 subunit is defective due to a β2 mutation associated with Brugada syndrome.

Background Information: Cardiac channelopathies arise by mutations in genes encoding ion channel subunits. One example is Brugada Syndrome (BrS), which causes arrhythmias and sudden death. BrS is often associated with mutations in SCN5A, encoding Na 1.5, the α subunit of the major cardiac voltage-gated sodium channel. This channel forms a protein complex including one or two associated β subunits as well as other proteins.

Results: We analysed regulation of Na 1.5 localisation and trafficking by β2, specifically, Na 1.5 arrival to the cell surface. We used polarised Madin-Darby canine kidney (MDCK) cells and mouse atria-derived HL-1 cells, which retain phenotypic features of adult cardiomyocytes. In both, Na 1.5 was found essentially intracellular, mainly in the endoplasmic reticulum, whereas β2 localised to the plasma membrane, and was restricted to the apical surface in MDCK cells. A fraction of β2 interacted with Na 1.5, despite their limited overlap. Importantly, β2 promoted Na 1.5 localisation to the cell surface. Both β2 WT and the BrS-associated mutation D211G (substitution of Asp for Gly) effectively reached the plasma membrane. Strikingly, however, β2 D211G was defective in promoting Na 1.5 surface localisation.

Conclusions: Our data sustain that β2 promotes surface localisation of Na 1.5, which can be affected due to β2 mutations associated with channelopathies.

Significance: Our findings add to the understanding of β2 role in Na 1.5 trafficking and localisation, which must influence cell excitability and electrical coupling in the heart. This study will contribute to knowledge on development of arrhythmias.