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Related Concept Videos

Cardiac Action Potential01:30

Cardiac Action Potential

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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
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Electrophysiology of Normal Cardiac Rhythm01:19

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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...
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Conduction System of the Heart01:19

Conduction System of the Heart

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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.
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Conduction System of the Heart01:20

Conduction System of the Heart

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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.
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Action Potential: Phases of Stimulation01:28

Action Potential: Phases of Stimulation

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The action potential is a complex electrical event that occurs in excitable cells, such as neurons and muscle cells. It consists of several distinct phases, each with specific characteristics.
Resting Phase:
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The Cardiac Cycle01:13

The Cardiac Cycle

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The heart beats rhythmically in a sequence called the cardiac cycle—a rapid coordination of contraction (systole) and relaxation (diastole).
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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...
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Related Experiment Video

Updated: Nov 1, 2025

Methods for the Isolation, Culture, and Functional Characterization of Sinoatrial Node Myocytes from Adult Mice
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Methods for the Isolation, Culture, and Functional Characterization of Sinoatrial Node Myocytes from Adult Mice

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HCN4 current during human sinoatrial node-like action potentials.

Maaike Hoekstra1, Antoni C G van Ginneken1, Ronald Wilders1

  • 1Department of Medical Biology, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands.

Progress in Biophysics and Molecular Biology
|June 21, 2021
PubMed
Summary
This summary is machine-generated.

The hyperpolarization-activated funny current (If) contributes to human sinoatrial node (SAN) cell depolarization. Its amplitude is finely tuned by heart rate, beta-adrenergic stimulation, and atrial load.

Keywords:
Action potential clampHeart rateHumanHyperpolarization-activated currentSinoatrial nodeβ-adrenergic stimulation

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Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents
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Area of Science:

  • Cardiovascular Physiology
  • Cardiac Electrophysiology

Background:

  • The role of the hyperpolarization-activated funny current (If), mediated by HCN4 channels, in human sinoatrial node (SAN) pacemaker activity remains debated.
  • Previous studies have not fully elucidated the precise contribution of If to SAN function.

Purpose of the Study:

  • To investigate the contribution of If to diastolic depolarization in human SAN cells.
  • To determine the dependence of If on heart rate, cAMP levels (simulated by forskolin), and atrial load.

Main Methods:

  • HCN4 channels were expressed in human cardiac myocyte progenitor cells (CMPCs).
  • Perforated patch-clamp technique was used in voltage-clamp and action potential clamp modes with human SAN-like waveforms (500-1500 ms cycle length).
  • Experiments were conducted with and without forskolin and with a voltage offset to simulate atrial load.

Main Results:

  • Forskolin increased HCN4 current density by 14% and shifted activation by +7.4 mV, accelerating activation and slowing deactivation.
  • HCN4 current amplitude increased with longer cycle lengths and was enhanced by forskolin and a negative voltage offset.
  • The If current did not fully deactivate during the diastolic depolarization phase.

Conclusions:

  • The If current is active during human SAN action potential waveforms.
  • If amplitude is dynamically modulated by heart rate, beta-adrenergic stimulation, and diastolic voltage, indicating delicate physiological control.