Modulation of cardiac gap junction expression and arrhythmic susceptibility

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Cardiac Electrophysiology

Background:

• Connexin43 (Cx43) is the primary gap junction protein in the ventricles, essential for normal cardiac electrical conduction.
• Loss of Cx43 in the heart leads to sudden arrhythmic death in mice.
• Mechanisms linking reduced Cx43 and ventricular arrhythmias are not fully understood.

Purpose of the Study:

• To investigate the relationship between progressively decreasing levels of Cx43 and the susceptibility to malignant ventricular arrhythmias.
• To characterize arrhythmic susceptibility in a novel murine model with gradual, heart-specific Cx43 deficiency.

Main Methods:

• Generation of cardiac-restricted Cx43 conditional knockout (CKO) mice with progressively decreasing Cx43 levels (O-CKO mice).
• Assessment of Cx43 protein levels, cardiac conduction velocity, and inducibility of ventricular tachyarrhythmias at different ages.
• Evaluation of hemodynamic measurements and ventricular effective refractory period.

Main Results:

• O-CKO mice exhibited premature death but lived longer than initial CKO mice.
• At 45 days, Cx43 levels dropped to 18% of control, conduction velocity halved, and 80% of mice developed inducible lethal tachyarrhythmias.
• Arrhythmia susceptibility was not linked to altered hemodynamics or refractory period.

Conclusions:

• Gradual reduction in cardiac Cx43 abundance significantly slows impulse propagation.
• Moderately severe Cx43 deficiency dramatically increases susceptibility to inducible ventricular arrhythmias.
• Cx43 levels are critical for maintaining normal cardiac electrical stability and preventing arrhythmias.