Sodium channel selectivity filter regulates antiarrhythmic drug binding

Area of Science:

• Molecular Pharmacology
• Ion Channel Physiology
• Drug Discovery

Background:

• Local anesthetic antiarrhythmic drugs are crucial for treating cardiac arrhythmias.
• The precise molecular mechanism of sodium channel (Na+) blockade by these drugs remains unclear.
• These drugs possess a charged amino group and a hydrophobic tail, suggesting specific interaction sites.

Purpose of the Study:

• To elucidate the molecular mechanism of Na+ channel blockade by local anesthetics.
• To investigate the role of the Na+ channel selectivity filter in drug interaction.
• To identify specific residues within the channel pore involved in drug binding and access.

Main Methods:

• Site-directed mutagenesis of the adult rat skeletal muscle Na+ channel (micro1).
• Assessment of Na+ channel block using lidocaine and its derivatives (QX314, QX222).
• Utilized neurotoxins (neo-saxitoxin, tetrodotoxin) to probe channel pore accessibility.

Main Results:

• Mutations in the selectivity filter (e.g., K1237E) altered resting lidocaine block, indicating electrostatic interactions.
• External application of charged lidocaine derivatives (QX314, QX222) was enabled by mutations in selectivity filter residues (D400A, E755A, A1529D).
• The selectivity filter and adjacent S6 segments are critical for drug access and binding within the Na+ channel pore.

Conclusions:

• The Na+ channel selectivity filter directly interacts with the charged portion of local anesthetic drugs.
• The selectivity filter regulates the access and egress of drugs to their binding site within the pore.
• This study reveals the structural basis for Na+ channel blockade by local anesthetics, implicating the selectivity filter and S6 segments.