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Related Concept Videos

The Cardiac Cycle01:13

The Cardiac Cycle

The heart beats rhythmically in a sequence called the cardiac cycle—a rapid coordination of contraction (systole) and relaxation (diastole).
The Process
Electrical signals—sent from the sinoatrial (SA) node in the right atrial wall to the atrioventricular (AV) node between the right atrium and right ventricle—cause both atria to simultaneously contract. When the signal reaches the AV node, it pauses for approximately a tenth of a second, allowing the atria to contract and empty blood into the...
Electrophysiology of Normal Cardiac Rhythm01:19

Electrophysiology of Normal Cardiac Rhythm

The normal cardiac rhythm is a synchronized electrical activity that facilitates the regular and coordinated contraction of the heart muscle. This process is essential for efficient blood circulation throughout the body. The fundamental elements involved in establishing and maintaining this rhythm include the unique electrical properties of cardiac muscle cells, the sinoatrial (SA) node's pacemaker function, the specialized conducting system, and the ionic mechanisms underlying each phase of...
Conduction System of the Heart01:19

Conduction System of the Heart

Autorhythmicity is a term that refers to the heart's inherent ability to generate electrical signals and instigate muscle contractions. This self-regulating conduction system within the heart consists of two key components: the pacemaker cells and specialized conducting cells.
The pacemaker cells are located in two primary nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node pacemaker cells can autonomously depolarize, triggering an action potential that leads to the...
Conduction System of the Heart01:20

Conduction System of the Heart

The cardiac conduction system produces and transmits electrical impulses that prompt myocardial contraction, ensuring efficient heart function. This intricate system ensures that the heart beats in a coordinated and efficient manner, beginning with the atria and then the ventricles. The conduction system optimizes cardiac output by maintaining this precise sequence, which is crucial for adequate blood circulation.
This system relies on the unique properties of nodal and Purkinje cells:...
Cardiac Action Potential01:30

Cardiac Action Potential

Cardiac action potentials are essential for proper heart function, enabling the rhythmic contractions needed for adequate blood circulation. Nodal cells and Purkinje fibers, specialized for electrical conduction, generate these action potentials.
The cardiac action potential process involves a series of phases characterized by the movement of ions across the cardiac cell membranes, leading to the depolarization and repolarization of the cardiac myocytes.
Ionic Basis of Cardiac Action Potentials
ECG Interpretation of Arrhythmias I: Sinus Arrhythmias01:16

ECG Interpretation of Arrhythmias I: Sinus Arrhythmias

Arrhythmias are disturbances in the heart's rhythm that lead to abnormal heartbeats. These irregularities can originate from different parts of the heart and are classified based on their origin and nature.
Types of Arrhythmias
Sinus Node Arrhythmias
Sinus Bradycardia: Originating from the sinoatrial (SA) node, sinus bradycardia involves slower impulses, resulting in a heart rate of less than 60 beats per minute (bpm). Causes include sleep, vagal stimulation, beta-blockers, hypothyroidism, and...

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Related Experiment Video

Updated: Jun 22, 2026

Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection
08:52

Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection

Published on: February 17, 2015

The pacemaker current in the sinus node.

D DiFrancesco1

  • 1Dipartimento di Fisiologia e Biochimica Generali, Elettrofisiologia, Milano, Italy.

European Heart Journal
|December 1, 1987
PubMed
Summary
This summary is machine-generated.

The cardiac pacemaker current (if) generates heart rhythm. Surprisingly, acetylcholine inhibits this current, challenging the view that potassium channels solely slow heart rate.

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Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice
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Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice
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Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

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Area of Science:

  • Cardiac electrophysiology
  • Ion channel function
  • Autonomic regulation of heart rate

Background:

  • The sino-atrial (SA) node generates the heart's electrical rhythm.
  • The hyperpolarization-activated current (if) is crucial for diastolic depolarization in SA node cells.
  • Catecholamines accelerate heart rate by modulating the if current.

Purpose of the Study:

  • To investigate the role of the if current in cardiac pacemaker activity.
  • To examine the effect of acetylcholine on the if current.
  • To re-evaluate the mechanism of acetylcholine-induced heart rate slowing.

Main Methods:

  • Recording of the if current in isolated sino-atrial node cells.
  • Application of hyperpolarizing voltage stimuli.
  • Pharmacological manipulation using acetylcholine.

Main Results:

  • The if current was recorded during hyperpolarization in the diastolic voltage range.
  • The if current, carried by Na+ and K+, is inward in the pacemaker potential range.
  • Low doses of acetylcholine were found to strongly inhibit the if current.

Conclusions:

  • The if current is a key determinant of the pacemaker depolarization phase.
  • Acetylcholine's inhibitory action on the if current provides a novel mechanism for heart rate regulation.
  • This finding challenges the traditional understanding of acetylcholine's effect on cardiac pacing, suggesting a direct modulation of the if current, not solely K+ channel activation.