Disturbed atrio-ventricular conduction and normal contractile function in isolated hearts from Cav1.3-knockout mice

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Ion Channel Function

Background:

• Cardiac L-type calcium channels (Cav1.2 and Cav1.3) regulate heart function.
• Cav1.3 channels are highly expressed in the sino-atrial node (SAN) and atria, unlike Cav1.2.
• Cav1.3 knockout mice exhibit bradycardia, suggesting a role in cardiac rhythm.

Purpose of the Study:

• To investigate the functional role of Cav1.3 channels in the working heart.
• To determine the impact of Cav1.3 suppression on ventricular contractility and cardiac electrophysiology.
• To explore Cav1.3 as a potential pharmacological target for bradycardic agents.

Main Methods:

• Utilized isolated working hearts from wild-type and Cav1.3 knockout mice.
• Performed histological analysis to assess cardiac pathology.
• Recorded electrocardiograms (ECGs) and measured ventricular contractility.
• Assessed the effects of isoproterenol on cardiac function and electrophysiology.

Main Results:

• Cav1.3 knockout hearts showed no pathological changes and maintained normal ventricular contractility.
• Severe sinus bradycardia and ventricular extrasystoles were observed in Cav1.3 knockout hearts, partially improved by isoproterenol.
• Delayed atrio-ventricular (AV) conduction and a decoupling of heart rate and PR interval were evident.
• Isoproterenol did not ameliorate the AV conduction disturbances.

Conclusions:

• Cav1.3 channel suppression does not impair ventricular contractile function.
• Reduced sinus node frequency is compensated by adrenergic stimulation, but AV node dysfunction persists.
• Bradyarrhythmia in Cav1.3 deficient hearts involves intrinsic AV node dysfunction resistant to adrenergic effects.
• Findings predict the clinical presentation of selective Cav1.3 blockade.