Beta-receptor activation increases sodium current in guinea pig heart

Area of Science:

• Cardiology
• Electrophysiology
• Molecular Pharmacology

Background:

• Sympathetic excitation increases cardiac output via beta-adrenergic signaling.
• The precise role of sodium channel modulation in this response requires further elucidation.

Purpose of the Study:

• To investigate the impact of beta-receptor activation on cardiac sodium channel currents.
• To determine the physiological significance of altered sodium current in sympathetic-induced increases in cardiac output.

Main Methods:

• Utilized guinea pig hearts and isolated ventricular myocytes.
• Employed ECG, microelectrode action potential recordings, whole-cell and single-channel current measurements, and pumping-force assessments.

Main Results:

• Isoprenaline dose-dependently shortened QRS waves and increased action potential amplitude and Vmax.
• Augmented fast sodium current and altered sodium channel gating modes (long-open, burst) were observed.
• Increased cAMP levels mimicked these effects; TTX reversed isoprenaline-induced pumping force increase in the presence of a calcium channel blocker.

Conclusions:

• Beta-adrenergic stimulation enhances inward sodium current by modifying sodium channel gating.
• Accelerated ventricular conduction velocity and improved cardiac pumping function are potential consequences.
• Synchronous cardiac contraction may be facilitated by these electrophysiological changes.