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Related Concept Videos

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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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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The Role of Actin and Myosin in Non-muscle Cells01:10

The Role of Actin and Myosin in Non-muscle Cells

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Actin and myosin or actomyosin filaments also play a significant role in cells other than those involved in muscle contraction (which occurs within the sarcomere of muscle cells). The mechanism of non-muscle cell contractile bundles was first observed in Dictyostelium and Acanthamoeba. In non-muscle cells, two bundles are commonly found: stress fibers and actomyosin adherence belts. These contractile bundles are smaller and less organized than the ones found in muscle cells. They  are held...
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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.
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...
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Overview of Skeletal Muscle01:15

Overview of Skeletal Muscle

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Skeletal muscles are composed of a bundle of muscle fibers and are attached to bones through tendons. Each skeletal muscle fiber is a single muscle cell. The sarcolemma, the plasma membrane of a skeletal muscle cell, consists of a lipid bilayer and glycocalyx that supports muscle fibers. The sarcolemma extends into the muscle cells to form tubular structures called transverse or T-tubules. Each side of the T-tubules consists of a membrane-bound structure called the sarcoplasmic reticulum,...
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Cross-bridge Cycle01:26

Cross-bridge Cycle

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As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.
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Characterization at the Molecular Level using Robust Biochemical Approaches of a New Kinase Protein
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LKB1/Mo25/STRAD uniquely impacts sarcomeric contractile function and posttranslational modification.

Samantha M Behunin1, Marissa A Lopez-Pier1, Camille L Birch1

  • 1Sarver Molecular Cardiovascular Research Program, Department of Physiology, University of Arizona, Tucson, Arizona.

Biophysical Journal
|March 27, 2015
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Summary
This summary is machine-generated.

The LKB1 complex/AMPK ratio impacts cardiac myofilament function and cross-bridge dynamics. The LKB1 complex alone suppresses myofilament function and alters cardiac Troponin I phosphorylation.

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Area of Science:

  • Cardiovascular Physiology
  • Cellular Energetics
  • Molecular Cardiology

Background:

  • Cardiac disease involves metabolic and energetic remodeling of the myocardium.
  • Changes in adenine nucleotide pools activate AMP-activated protein kinase (AMPK), a key regulator of cellular energy.
  • The LKB1 complex (liver kinase B 1, mouse protein 25, STE-related adaptor protein) phosphorylates and activates AMPK.

Purpose of the Study:

  • To investigate how varying stoichiometric ratios of the LKB1 complex to AMPK affect myofilament function.
  • To determine if the LKB1 complex can modulate AMPK targeting and myofilament function independently of AMPK activation.

Main Methods:

  • Demembranated rat cardiac trabeculae were incubated with different ratios of the LKB1 complex and AMPK, or with the LKB1 complex alone.
  • Measurements included Ca(2+) sensitivity of tension, tension redevelopment rate, maximum tension, length-dependent activation, cooperativity, and sarcomeric protein phosphorylation.
  • Phospho-proteomic analysis identified changes in cardiac Troponin I (cTnI) and myosin-binding protein C phosphorylation.

Main Results:

  • Myofilament Ca(2+) sensitivity and cross-bridge dynamics were dependent on the LKB1 complex/AMPK ratio.
  • The LKB1 complex suppressed myofilament function independently of AMPK.
  • LKB1 complex treatment alone increased myosin-binding protein C phosphorylation but did not alter cTnI phosphorylation or phosphospecies distribution.

Conclusions:

  • The LKB1/AMPK signaling axis alters cardiac muscle function through multiple mechanisms.
  • The ratio of LKB1 complex to AMPK influences myofilament properties.
  • The LKB1 complex exerts effects on myofilament function independent of its role in AMPK activation.