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Related Concept Videos

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...
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
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:...
Specialized Characteristics of Cardiac Muscles01:27

Specialized Characteristics of Cardiac Muscles

The primary role of cardiac muscles is to propel blood throughout the cardiovascular system. The cardiac muscle cells, or cardiomyocytes, exhibit specialized characteristics that allow them to perform this function.
Cardiac muscle cells are smaller than skeletal muscles, averaging 10–20 mm in diameter and 50–100 mm in length. However, they have large energy demands for continuous contraction and relaxation. This energy is almost exclusively derived from aerobic metabolism of energy reserves in...
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...

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Related Experiment Video

Updated: Jun 21, 2026

Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice
09:20

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

Published on: July 5, 2021

The cardiac pacemaker current.

Mirko Baruscotti1, Andrea Barbuti, Annalisa Bucchi

  • 1Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, Università degli Studi di Milano, Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata (CIMMBA), via Celoria 26, 20133 Milano, Italy. mirko.baruscotti@unimi.it

Journal of Molecular and Cellular Cardiology
|July 14, 2009
PubMed
Summary
This summary is machine-generated.

The pacemaker current I(f), carried by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, primarily controls heart rate. HCN4 channels are crucial for sinoatrial node pacemaking and are targeted by heart rate-reducing drugs.

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Area of Science:

  • Cardiology
  • Molecular Biology
  • Electrophysiology

Background:

  • Cardiac rate in mammals is dictated by the diastolic depolarization duration in sinoatrial node (SAN) cells.
  • This depolarization is mainly governed by the pacemaker I(f) current, mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (HCN1-4).
  • HCN4 is the predominant isoform in the SAN, and its role in pacemaking is evidenced by loss-of-function mutations causing cardiac rate disturbances.

Purpose of the Study:

  • To review recent findings on the contribution of f/HCN channels to cardiac pacemaking.
  • To highlight the significance of the I(f) current as a pharmacological target for heart rate modulation.
  • To discuss the role of HCN proteins in both physiological pacemaking and pathological conditions.

Main Methods:

  • Literature review focusing on recent research findings.
  • Analysis of the role of HCN channel isoforms in cardiac conduction system cells.
  • Examination of the pharmacological targeting of the I(f) current.

Main Results:

  • HCN4 is the most abundant HCN isoform in the SAN and is critical for normal heart rate.
  • Mutations in HCN genes can lead to cardiac rate disturbances.
  • The I(f) current is a validated target for drugs like ivabradine, used to reduce heart rate.
  • HCN channels are expressed at low levels in working myocytes but can be arrhythmogenic when overexpressed pathologically.

Conclusions:

  • HCN channels, particularly HCN4, are fundamental to cardiac pacemaking.
  • Dysregulation of HCN channel function can result in cardiac arrhythmias.
  • Targeting the I(f) current offers a therapeutic strategy for managing heart rate.