Structural and Functional Characterization of a Na_v1.5-Mitochondrial Couplon.

Area of Science:

• Cardiology
• Cell Biology
• Molecular Biology

Background:

• The cardiac sodium channel Na_V1.5 is crucial for heart excitability and conduction.
• Sodium channels form clusters in specific cardiac myocyte subdomains, but their association with organelles is unclear.

Purpose of the Study:

• To characterize the subcellular domain of Na_V1.5 clusters and associated subsarcolemmal mitochondria.
• To investigate the functional consequences of this association on mitochondrial activity.

Main Methods:

• Super-resolution and electron microscopy to identify Na_V1.5 and mitochondrial proximity.
• Assessment of mitochondrial calcium (Ca²⁺) and reactive oxygen species (ROS) production.
• Transcriptional analysis of SCN5A and SLC8B1 correlation.

Main Results:

• Identified a Na_V1.5 subpopulation near subsarcolemmal mitochondria, which host the NCLX exchanger.
• Mitochondria near Na_V1.5 channels showed increased Ca²⁺ accumulation and ROS production upon tetrodotoxin (TTX) exposure.
• SCN5A and SLC8B1 expression were negatively correlated in human datasets.

Conclusions:

• Described a novel cardiac 'couplon' formed by Na_V1.5 clusters and mitochondria.
• Demonstrated functional coupling where Na_V1.5 activity influences mitochondrial Ca²⁺ extrusion via NCLX.
• Provided mechanistic insight into the interplay between cardiac electrical and mitochondrial functions.