Lateral Membrane-Specific MAGUK CASK Down-Regulates NaV1.5 Channel in Cardiac Myocytes

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Ion Channel Physiology

Background:

• Cardiac myocyte function relies on precise membrane protein localization.
• The NaV1.5 sodium channel is critical for cardiac action potentials.
• NaV1.5 localizes to various membrane domains and interacts with multiple proteins.

Purpose of the Study:

• To investigate the interaction between CASK and NaV1.5 in cardiac myocytes.
• To determine if CASK regulates NaV1.5 localization and function.

Main Methods:

• Immunostaining to determine CASK localization.
• Whole-cell patch clamp electrophysiology to measure sodium current (INa).
• CASK knockdown (silencing) in vitro and in vivo.
• Pull-down assays for protein interaction analysis.
• Total Internal Reflection Fluorescence microscopy and biotinylation assays for surface expression.
• Brefeldin-A treatment to assess protein transport.

Main Results:

• CASK localizes to the lateral membranes of cardiac myocytes, associated with dystrophin.
• CASK silencing increased INa and NaV1.5 surface expression at the lateral membrane.
• CASK directly interacts with the C-terminus of NaV1.5.
• CASK silencing reduced syntrophin but not NaV1.5 or dystrophin levels.
• Increased NaV1.5 surface expression was linked to altered ion channel trafficking.

Conclusions:

• CASK directly binds to NaV1.5.
• CASK regulates NaV1.5 surface expression at the lateral membrane.
• This interaction controls cardiac sodium channel trafficking and function.