Related Experiment Video
Updated: Aug 12, 2026
12:10
Measuring Fast Calcium Fluxes in Cardiomyocytes
Published on: November 29, 2011
Large currents generate cardiac Ca2+ sparks
L T Izu1, J R Mauban, C W Balke
1Department of Medicine, University of Maryland, Baltimore, Baltimore, Maryland 21201, USA. lizu@umaryland.edu
Biophysical Journal
|February 13, 2001
Summary
Cardiac calcium (Ca2+) sparks are larger than previously modeled, requiring significantly higher Ca2+ currents (10-20 pA) through calcium release units (CRUs) to explain observed spark sizes and durations.
Area of Science:
- Cardiovascular Physiology
- Calcium Signaling
- Biophysics
Background:
- Previous models of cardiac Ca2+ sparks assumed low Ca2+ currents (1-2 pA) and smaller spark amplitudes (F/F(0) ~2.0, FWHM ~1 µm).
- These models did not fully account for the observed characteristics of experimentally measured Ca2+ sparks.
Purpose of the Study:
- To present actual cardiac Ca2+ spark data with larger amplitudes and widths.
- To develop a mathematical model that explains these larger sparks.
- To determine the necessary Ca2+ currents through calcium release units (CRUs) to generate observed spark properties.
Main Methods:
- Analysis of experimentally recorded cardiac Ca2+ sparks.
- Development of a mathematical model incorporating Ca2+ dynamics and CRU currents.
- Simulation of spark generation under varying current densities and buffering conditions.
Main Results:
- Observed Ca2+ sparks exhibited peak fluorescence ratios (F/F(0)) >6 and full-width at half maximum (FWHM) ~2 µm.
- The mathematical model indicated a lower bound of ~11 pA for CRU current under ideal conditions.
- Realistic conditions necessitate CRU currents of approximately 20 pA to generate 2-µm Ca2+ sparks.
- Spark amplitudes (F/F(0)) were significantly larger (6-12) for currents ≥5 pA.
- Simulations showed that clustered CRUs, each producing ~10 pA, could also generate wider sparks.
Conclusions:
- Cardiac Ca2+ sparks possess significantly larger peak amplitudes than previously assumed.
- The observed spark dimensions (FWHM ~2 µm) are consistent with larger underlying Ca2+ currents (10-20 pA).
- The findings necessitate a revision of existing models of calcium release unit function in cardiac cells.
Related Concept Videos
01:13The 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...
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...
01:27Specialized 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...
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...
01:19Electrophysiology 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...
01:28Mechanism of Cardiac Arrhythmias
Arrhythmias are irregular heart rhythms occurring when the heart's electrical impulses become abnormal. These disturbances can lead to various symptoms, depending on their severity and the underlying cause. Some common factors contributing to arrhythmias include hypoxia, ischemia, electrolyte imbalances, excessive catecholamine exposure, drug toxicity, and muscle overstretching. Arrhythmias can be classified into two main types based on the rate and site of origin of abnormal heart rhythms.
01:25Correlation between ECG and Cardiac Cycle
The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac cycle.
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...
01:30Cardiac 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
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