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Related Concept Videos

Structure of Cardiac Muscles01:13

Structure of Cardiac Muscles

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Cardiac muscle, or myocardium, is a specialized type of muscle found exclusively in the heart. Its unique structural and functional characteristics enable the heart to perform its vital role of pumping blood throughout the body continuously and rhythmically. The cardiac muscle cells, or cardiomyocytes, possess an endomysium and perimysium but do not have an epimysium.
Compared to skeletal muscles, cardiac muscle cells are small and mostly have a single nucleus. Additionally, they are usually...
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The Sarcomere01:08

The Sarcomere

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A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each...
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Specialized Characteristics of Cardiac Muscles01:27

Specialized Characteristics of Cardiac Muscles

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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...
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Smooth Muscle Contraction01:25

Smooth Muscle Contraction

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Smooth muscle contraction is a complex process vital for various bodily functions, from maintaining blood vessel tension to facilitating the movement of food through the digestive tract. Unlike striated muscles, smooth muscle contraction begins more slowly and lasts longer.
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Excitation-Contraction Coupling in Skeletal Muscles01:20

Excitation-Contraction Coupling in Skeletal Muscles

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Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at the triad, a structure found in skeletal muscle fibers that comprise a T-tubule and terminal cisternae of the sarcoplasmic reticulum on each side. These triads are visible in longitudinally sectioned muscle fibers. They are typically located at the A-I junction — the junction between the A and I bands of the sarcomere.
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Actin and Myosin in Muscle Contraction01:16

Actin and Myosin in Muscle Contraction

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Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...
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Updated: Jul 24, 2025

Sarcomere Shortening of Pluripotent Stem Cell-Derived Cardiomyocytes using Fluorescent-Tagged Sarcomere Proteins.
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Sarcomere Shortening of Pluripotent Stem Cell-Derived Cardiomyocytes using Fluorescent-Tagged Sarcomere Proteins.

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Stretch Harmonizes Sarcomere Strain Across the Cardiomyocyte.

Jia Li1,2, Joakim Sundnes3, Yufeng Hou1,2

  • 1Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Norway (J.L., Y.H., M.L., M.R., T.R.K., M.F., P.A.N., I.E.S., O.M.S., I.G.L., W.E.L.).

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Cardiomyocyte contraction increases with stretch by recruiting more sarcomeres to shorten. Titin protein regulates this process, and its reduced expression impairs heart muscle contractility.

Keywords:
connectinmyocytes, cardiacsarcomeres

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In Vitro Assessment of Cardiac Function Using Skinned Cardiomyocytes

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Area of Science:

  • Cardiovascular Physiology
  • Muscle Biology
  • Cellular Mechanics

Background:

  • The Frank-Starling mechanism describes increased cardiomyocyte contraction with myocardial stretch.
  • The precise sarcomere-level mechanisms driving this phenomenon remain incompletely understood.
  • Investigating intersarcomere dynamics during cell lengthening is crucial.

Purpose of the Study:

  • To elucidate how sarcomere contractile synchrony and intersarcomere dynamics enhance cardiomyocyte contractility during stretch.
  • To determine the role of titin in regulating these dynamics.

Main Methods:

  • Simultaneous recording of sarcomere strain and intracellular calcium (Ca2+) in isolated cardiomyocytes.
  • Experiments conducted at resting length and following stepwise cell lengthening.
  • Utilized rat and titin-haploinsufficient mouse models.

Main Results:

  • Unstretched cardiomyocytes exhibit nonuniform sarcomere deformation, with some sarcomeres stretching or remaining stationary.
  • Cell lengthening recruits additional shortening sarcomeres, improving contractile efficiency.
  • Titin haploinsufficiency leads to increased sarcomere length variability, reduced recruitment of shortening sarcomeres, and impaired contractility.

Conclusions:

  • Sarcomere recruitment and strain harmonization are key to increased contractility during cell stretch.
  • Titin plays a critical role in setting sarcomere dimensions and controlling sarcomere recruitment.
  • Reduced titin expression impairs cardiomyocyte contractility through altered intersarcomere dynamics.