Mutant voltage-gated Na⁺ channels can exert a dominant negative effect through coupled gating

Area of Science:

• Molecular Biology
• Neuroscience
• Cardiology

Background:

• Mutations in voltage-gated sodium channels (Na_v) are linked to channelopathies like cardiac arrhythmias and epilepsy.
• Previously, dominant negative effects of Na_v mutants were attributed to impaired trafficking of wild-type (WT) channels.
• Na_v channels are known to form dimers with coupled gating properties.

Purpose of the Study:

• To investigate if coupled gating of Na_v channel dimers contributes to the dominant negative effect of mutations.
• To differentiate the mechanisms of dominant negative effects: trafficking deficiency versus altered gating.

Main Methods:

• Cell surface biotinylation to assess channel trafficking.
• Single channel recordings to analyze gating probability and coupled gating of Na_v channel dimers.
• Coexpression of WT Na_v1.5 with a trafficking-competent mutant (Na_v1.5-L325R).

Main Results:

• The Na_v1.5-L325R mutant trafficked to the cell surface, but coexpression with WT channels reduced Na⁺ current by 75% without altering total surface expression.
• Single channel recordings revealed impaired gating probability and coupled gating in WT:L325R dimers.
• The L325R mutation exerted a dominant negative effect at the gating level, not solely through trafficking interference.

Conclusions:

• Dominant negative effects of Na_v1.5 mutants can arise from impaired WT channel gating probability due to altered coupled gating of dimers.
• This mechanism, involving dimerization and coupled gating, provides a new understanding of dominant negative suppression in Na_v channelopathies.
• This finding supports the role of coupled gating in Na_v channelopathies like Brugada syndrome.