Increased Ca²⁺ Sequestration by the Sarco-/Endoplasmic Reticulum in Cardiac Purkinje Cells After Myocardial...

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Molecular Cardiology

Background:

• Ischemia during acute coronary occlusion is a primary driver of ischemia-reperfusion injury (IRI).
• Ischemic arrhythmias, particularly ventricular arrhythmias, originate in Purkinje cells (Pcells) due to abnormal calcium (Ca2+) dependent depolarizations.
• Increased sarcoplasmic reticulum (SR) Ca2+ release in Pcells is implicated in these arrhythmias, potentially linked to augmented SERCA2 pump expression.

Purpose of the Study:

• To investigate the impact of ischemia on SR Ca2+ uptake dynamics in live Pcells.
• To test the hypothesis that increased SERCA2 expression enhances SR Ca2+ sequestration and release in Pcells during ischemia.
• To elucidate the role of altered intracellular Ca2+ handling in the conduction system during myocardial infarction (MI) and its contribution to arrhythmogenicity.

Main Methods:

• Utilized high-resolution confocal microscopy in a canine model of LAD coronary ligation to assess SR Ca2+ uptake in Pcells.
• Compared Ca2+ events (peripheral Ca2+ wavelets and central cell-wide waves) in Pcells from normal hearts versus hearts 48 hours post-coronary occlusion.
• Employed computational modeling to validate experimental findings on Ca2+ uptake rates and their effect on SR Ca2+ release.

Main Results:

• Forty-eight hours post-ischemia, SR Ca2+ spark firing rate increased by 60% at individual release sites, indicating accelerated intra-SR Ca2+ cycling.
• Resting Ca2+ restoration in peripheral Pcells (Wlets) accelerated by 37%, consistent with enhanced SR Ca2+ uptake at the cell periphery.
• Computational modeling confirmed that a 35% increase in Ca2+ uptake rate sufficiently explains the pro-arrhythmic SR Ca2+ release observed in Pcells after MI.

Conclusions:

• Augmented SERCA activity and increased SR Ca2+ uptake in the periphery of Pcells contribute to the arrhythmogenicity of Purkinje fibers in ischemic hearts.
• Ischemia-induced pro-arrhythmic remodeling of intracellular Ca2+ handling in the cardiac conduction system likely promotes triggered activity during subsequent reperfusion.
• Understanding these ischemia-mediated alterations in Ca2+ dynamics is crucial for elucidating the mechanisms underlying ischemia-reperfusion injury and developing therapeutic strategies.