Nadolol block of Nav1.5 does not explain its efficacy in the long QT syndrome

Area of Science:

• Cardiovascular Pharmacology
• Molecular Cardiology
• Ion Channel Physiology

Background:

• Beta-adrenergic receptor antagonists (β-blockers) are primary treatments for long QT syndrome.
• Efficacy varies among β-blockers; propranolol and nadolol are more effective than metoprolol.

Purpose of the Study:

• To investigate the effects of propranolol, nadolol, and metoprolol on cardiac sodium channels (Nav1.5).
• To explore the hypothesis that nadolol's efficacy is due to a membrane-stabilizing effect, similar to propranolol.

Main Methods:

• Whole-cell patch-clamp recordings were used to assess drug effects on wild-type and mutant Nav1.5 channels.
• The study examined the impact of β-blockers on peak and persistent sodium currents.
• Biophysical properties, including voltage dependence of activation and inactivation, were analyzed.

Main Results:

• Nadolol exhibited a non-use-dependent block of peak sodium current but did not affect the persistent current in the LQT3 mutant.
• Propranolol demonstrated use-dependent block of peak current and reduced the persistent current in the LQT3 mutant.
• Metoprolol had no significant effect on either peak or persistent sodium current.

Conclusions:

• Nadolol and propranolol, but not metoprolol, alter the biophysical properties of Nav1.5 channels.
• These findings partially explain the differing clinical efficacy of nadolol and metoprolol.
• The study does not fully elucidate the similar clinical effectiveness of nadolol and propranolol.