Protein Phosphatase 2A Regulates Cardiac Na⁺ Channels

Area of Science:

• Cardiovascular physiology
• Molecular cardiology
• Ion channel regulation

Background:

• Voltage-gated sodium channels (Na_v1.5) are crucial for cardiac excitability.
• The late sodium current (I_Na,L) is implicated in life-threatening arrhythmias.
• Ca²⁺/calmodulin-dependent kinase II (CaMKII) enhances I_Na,L, but regulatory pathways are unknown.

Purpose of the Study:

• To identify phosphatase pathways regulating I_Na,L in vivo.
• To investigate the role of protein phosphatase 2A (PP2A) in cardiac sodium channel function.

Main Methods:

• Utilized a B56α knockout (KO) mouse model lacking a key PP2A regulatory subunit.
• Performed computational modeling and direct I_Na,L recordings in B56α KO myocytes.
• Examined CaMKII-dependent phosphorylation of Na_v1.5 and PP2A/B56α localization with Na_v1.5.

Main Results:

• B56α KO myocytes exhibited altered action potentials and reduced arrhythmogenic I_Na,L.
• PP2A/B56α was found to co-localize and co-immunoprecipitate with Na_v1.5.
• B56α KO myocytes showed decreased sensitivity to isoproterenol-induced I_Na,L and reduced Na_v1.5 phosphorylation.

Conclusions:

• PP2A, specifically the PP2A/B56α complex, negatively regulates Na_v1.5 activity in cardiomyocytes.
• This PP2A-mediated regulation is critical for controlling pathogenic I_Na,L.
• B56α represents a novel therapeutic target for managing cardiac arrhythmias.