Restoration of normal L-type Ca²⁺ channel function during timothy syndrome by ablation of an anchoring protein

Rationale: L-type Ca²⁺ (Ca_V1.2) channels shape the cardiac action potential waveform and are essential for excitation-contraction coupling in heart. A gain-of-function G406R mutation in a cytoplasmic loop of Ca_V1.2 channels causes long QT syndrome 8 (LQT8), a disease also known as Timothy syndrome. However, the mechanisms by which this mutation enhances Ca_V1.2-LQT8 currents and generates lethal arrhythmias are unclear. Objective: To test the hypothesis that the anchoring protein AKAP150 modulates Ca_V1.2-LQT8 channel gating in ventricular myocytes. Methods and Results: Using a combination of molecular, imaging, and electrophysiological approaches, we discovered that Ca_V1.2-LQT8 channels are abnormally coupled to AKAP150. A pathophysiological consequence of forming this aberrant ion channel-anchoring protein complex is enhanced Ca _V1.2-LQT8 currents. This occurs through a mechanism whereby the anchoring protein functions like a subunit of Ca_V1.2-LQT8 channels that stabilizes the open conformation and augments the probability of coordinated openings of these channels. Ablation of AKAP150 restores normal gating in Ca_V1.2-LQT8 channels and protects the heart from arrhythmias. Conclusion: We propose that AKAP150-dependent changes in Ca _V1.2-LQT8 channel gating may constitute a novel general mechanism for Ca_V1.2-driven arrhythmias.