Increased Risk for Atrial Alternans in Rabbit Heart Failure: The Role of Ca²⁺/Calmodulin-Dependent Kinase II and...

Area of Science:

• Cardiology
• Molecular Biology
• Electrophysiology

Background:

• Heart failure (HF) is a known risk factor for atrial fibrillation (AF), but the underlying molecular mechanisms remain unclear.
• Understanding the link between HF and AF is crucial for developing targeted therapies to prevent cardiac arrhythmias.

Purpose of the Study:

• To investigate the disturbances in calcium (Ca2+) signaling and electrophysiology in atrial myocytes from failing hearts.
• To identify the specific mechanisms contributing to the increased risk of atrial arrhythmias in HF.

Main Methods:

• Studied Ca2+ signaling and electrophysiology in rabbit atrial myocytes from normal and failing hearts.
• Utilized Ca2+ transient (CaT) alternans as an indicator of arrhythmogenicity.
• Investigated the roles of Ca2+/calmodulin-dependent kinase II (CaMKII) and IP3 signaling pathways.

Main Results:

• HF atrial myocytes exhibited increased susceptibility to CaT alternans, indicating higher arrhythmogenicity, despite unchanged action potential duration and only moderate decrease in L-type Ca2+ current.
• CaMKII inhibition effectively suppressed CaT alternans.
• While acute activation of IP3 signaling by endothelin-1 (ET-1) and angiotensin II (Ang II) transiently reduced CaT amplitude and sarcoplasmic reticulum (SR) Ca2+ load, prolonged exposure enhanced SR Ca2+ release and increased alternans. Inhibition of IP3 receptors mimicked these detrimental effects.

Conclusions:

• Activation of CaMKII and IP3 signaling pathways plays a significant role in promoting atrial arrhythmogenesis in the context of heart failure.
• These findings provide novel insights into the mechanisms linking HF to AF and suggest potential therapeutic targets.