The Autonomic Nervous System Regulates the Heart Rate through cAMP-PKA Dependent and Independent Coupled-Clock...

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Computational Biology

Background:

• Sinoatrial nodal cells (SANCs) control heart rate via spontaneous action potentials (APs).
• Autonomic nervous system modulation (adrenergic and cholinergic) influences SANC automaticity through adenylyl cyclase (AC) signaling.
• The precise mechanisms of cholinergic crosstalk and internal pacemaker regulation remain incompletely understood.

Purpose of the Study:

• To investigate the role of AC-cAMP/PKA signaling in mediating both positive and negative chronotropic modulation of SANC automaticity.
• To elucidate the interplay between membrane receptors, intracellular signaling cascades, and internal pacemaker mechanisms in regulating cardiac rate.
• To identify key molecular targets responsible for the crosstalk between cholinergic signaling and SANC firing rate reduction.

Main Methods:

• Utilized cultured adult rabbit pacemaker cells infected with an adenovirus expressing the FRET sensor AKAR3 to monitor PKA activity.
• Developed a mechanistic computational model integrating autonomic receptors, signaling cascades, membrane molecules, and internal pacemaker mechanisms.
• Performed experiments and simulations involving adrenergic (isoproterenol) and cholinergic (carbachol) stimulation, individually and in combination.

Main Results:

• PKA activity was tightly linked to SANC AP firing rate changes under both adrenergic and cholinergic stimulation.
• Computational model simulations accurately reproduced experimental findings, including accentuated antagonism.
• Disabling AC-cAMP-PKA signaling abolished the effect of autonomic receptor stimulation; inhibiting phospholamban modulation of SERCA impaired responses.
• Direct activation of internal pacemaker mechanisms mimicked the effects of autonomic receptor stimulation on AP firing rate.

Conclusions:

• AC-cAMP/PKA signaling is crucial for mediating autonomic nervous system effects on SANC firing rate.
• Both membrane and internal pacemaker mechanisms contribute to chronotropic regulation.
• Ca2+ and cAMP/PKA-dependent phosphorylation critically influence the rate and magnitude of cardiac rate changes.