Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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1A4; actin; alpha smooth muscle actin; alpha-smooth-muscle-actin; SMA; Smooth muscle actin

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Actin (from Greek actis = ray), a structural protein, is an essential component of the cytoskeleton. Actin forms a dense, stiff, three-dimensional cortical network of dynamic microfilaments that serve to stabilize the outer shape of a cell. At certain specific points of the cell, this network becomes increasingly dense, e.g. in membrane bulges (microvilli, pseudopodia, synapses) and at certain cell contacts (adherens junctions, tight junctions).

Together with other structural proteins such as myosin, troponin and tropomyosin, actin forms the central components for muscle contraction. In muscle cells, the proportion of actins is about 10%; in other cells, it is 1-5%. Actin contains bound ATP, which is hydrolyzed to ADP and inorganic phosphate during the polymerization of the microfilaments to become ADP and inorganic phosphate.

In humans 6 different isoforms are distinguished, differing only in a few amino acids. They are expressed in different tissue types.

  • alpha-actin
  • beta-actin
  • gamma actin

There is also an alpha heart muscle, an alpha and gamma smooth muscle, as well as a beta and a gamma non-muscular actin

Changes in the genes coding for actin can lead to muscle and other diseases.

Smooth muscle actin is found in the walls of blood vessels, the intestinal muscularis mucosae, the muscularis propria and in the stroma of various tissues.

Smooth muscle actin is also expressed in myofibroblasts and myoepithelial cells. It is used to identify leiomyomas, leiomyosarcomas.

Furthermore, various fibroblastically differentiated tumors, angiofibromas, various tumors of the body, and various tumor types are expressed in myofibroblasts and myoepithelial cells. angiomas, angiomas and various types of sarcoma express smooth muscle actin.

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Antibodies against smooth muscle (SMA) are used in chronically active hepatitis, polymyositis and as an accompanying phenomenon in various types of hepatitis. Virus infections.


Last updated on: 29.10.2020