Related Experiment Video
Updated: Aug 12, 2026

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice
Published on: September 17, 2015
NO-cGMP pathway increases the hyperpolarisation-activated current, I(f), and heart rate during adrenergic stimulation
N Herring1, L Rigg, D A Terrar
1University Laboratory of Physiology, University of Oxford, Parks Road, OX1 3PT, Oxford, UK.
The nitric oxide (NO)-cGMP pathway transiently increases heart rate (HR) via the I(f) current during adrenergic stimulation. This effect is limited by phosphodiesterase 2 (PDE2) activity.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Cardiac Electrophysiology
Background:
- The autonomic nervous system modulates heart rate (HR) through complex signaling pathways.
- The role of the nitric oxide (NO)-cGMP pathway in cardiac pacemaking, particularly its interaction with the L-type calcium current (I(CaL)) and hyperpolarization-activated current (I(f)), remains controversial.
- Understanding this pathway is crucial for comprehending cardiac autonomic control.
Purpose of the Study:
- To investigate the hypothesis that the NO-cGMP pathway, following adrenergic stimulation, activates phosphodiesterase 2 (PDE2) to attenuate cAMP-dependent stimulation of I(f) and HR.
- To elucidate the specific role of the NO-cGMP pathway in the autonomic modulation of sinoatrial node (SAN) function.
Main Methods:
- Experiments were conducted on guinea pig SAN/atria preparations and isolated SAN cells in the presence of norepinephrine (NE).
- The effects of the NO donor sodium nitroprusside (SNP) and 8Br-cGMP were assessed.
- Pharmacological agents including guanylyl cyclase inhibitor (ODQ), I(f) blockers (CsCl, ZD7288), and PDE2 inhibitor (EHNA) were utilized.
- RT-PCR was employed to confirm the presence of relevant phosphodiesterase (PDE) isoforms.
Main Results:
- Contrary to the hypothesis, SNP and 8Br-cGMP caused a transient increase in HR.
- This stimulatory effect on HR was dependent on the I(f) current, as it was abolished by I(f) blockers.
- SNP also increased I(f) in isolated SAN cells, and inhibition of PDE2 augmented and prolonged the SNP-induced HR increase.
- RT-PCR confirmed the expression of PDE2 and cGMP-inhibited PDE3 in SAN tissue.
Conclusions:
- Activation of the NO-cGMP pathway during adrenergic stimulation leads to a transient, I(f)-dependent increase in HR, not a decrease.
- The magnitude and duration of this stimulatory effect are regulated by PDE2 activity.
- These findings clarify the role of the NO-cGMP pathway in cardiac pacemaking under adrenergic influence.
Related Concept Videos
G-Protein Gated Ion Channels
Sensory organs,...
GPCRs Regulate Adenylyl Cylase Activity
Two...
cAMP-dependent Protein Kinase Pathways
Nitric Oxide Signaling Pathway
Adrenergic Receptors (Adrenoceptors): Classification
α-Adrenoceptors
α-Adrenoceptors are classified into two main subtypes: α1 and α2. The α1 adrenoceptors, which are found on postsynaptic...
Adrenergic Receptors: β Subtype
Isoprenaline > Adrenaline > Noradrenaline
Neurotransmitter binding to these receptors causes activation of adenylyl cyclase resulting in increased concentrations of cAMP and modulation of calcium ion channels within the cell. They are further classified into β1, β2, and β3 subtypes.
β1-adrenoceptors: β1-adrenoceptors have equal affinities for...

