L-Type Ca_v1.3 and HCN Channels Mediate Heart Rate Acceleration by Catecholamines.

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Ion Channel Function

Background:

• The precise ionic mechanisms driving catecholamine-induced heart rate increases remain unclear.
• Key players include sinoatrial node L-type Ca_v1.3 Ca²⁺ channels, Rad protein phosphorylation, and HCN channel regulation.

Purpose of the Study:

• To elucidate the roles of Ca_v1.3 channels, Rad phosphorylation, and HCN channel regulation in β-adrenergic heart rate control.
• To investigate the ionic basis of catecholamine-mediated acceleration of heart rate.

Main Methods:

• Studied mice lacking Ca_v1.3 channels or expressing modified Ca_v1.2 and HCN4 channels.
• Utilized pharmacological inhibition of cAMP-dependent HCN4 regulation and PKA-dependent Rad phosphorylation.
• Examined sinoatrial pacemaker myocyte activity and heart rate responses to sympathomimetics.

Main Results:

• Mice lacking Ca_v1.3 and cAMP-insensitive HCN4 showed no diurnal heart rate variation or response to catecholamines.
• Pharmacological inhibition of Ca_v1.3 blocked pacemaker enhancement when HCN regulation was silenced.
• Ca_v1.3 and HCN-mediated currents fully explained diastolic current changes upon β-adrenoceptor activation.

Conclusions:

• PKA phosphorylation of Rad disinhibits Ca_v1.3 channels and activates HCN channels, crucial for β-adrenergic heart rate regulation.
• Rad-mediated regulation of Ca_v1.3 and HCN channels explains catecholamine-induced heart rate acceleration.