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Membrane structure of nonactivated and activated human blood platelets as revealed by freeze-fracture: evidence for particle redistribution during platelet contraction.

Membrane structure of nonactivated and activated human blood platelets as revealed by... The distribution of intramembrane particles of nonactivated and activated human blood platelets was studied by freeze-fracture under various experimental conditions to see whether morphological evidence for a structural coupling between the platelet actomyosin system and the fibrin network in a retracting clot could be established. Membrane particles were evenly distributed in nonactivated platelets; the total number (E + P faces) was approximately 1,500/micrometers 2 of membrane, and there were two to three times more particles present on the E face than on the P face. Transformation of discoid platelets to "spiny spheres" by cooling did not change the particle distribution. Platelet activation and aggregation by serum or ADP caused no change in membrane particle density or distribution. Particle distribution was not changed in Ca2+-activated platelets fixed immediately before fibrin formation, but after fibrin formation and during clot retraction, particles were sometimes most frequent on the P face and tended to form distinct clusters, and aggregates of E face pits were observed. Blood platelets contain contractile proteins that are distinct as filaments in platelets in retracting clots. We suggest that the redistribution of particles seen in activated platelets during clot retraction reflects the esablishment of mechanical transmembrane links between the platelet actomyosin system and the fibrin net. The P-face particle clusters may represent sites of force transmission between actin filaments bonded to the inside of the membrane and the fibrin network at the outside. Thus, whereas membrane particles may not be directly involved in the attachment of actin filaments to membranes, the transmission of the force of the contractile system to an exterior substrate apparently involves the intramembrane particles. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Cell Biology Rockefeller University Press

Membrane structure of nonactivated and activated human blood platelets as revealed by freeze-fracture: evidence for particle redistribution during platelet contraction.

The Journal of Cell Biology , Volume 87 (1): 209 – Oct 1, 1980

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Publisher
Rockefeller University Press
Copyright
© 1980 Rockefeller University Press
ISSN
0021-9525
eISSN
1540-8140
DOI
10.1083/jcb.87.1.209
Publisher site
See Article on Publisher Site

Abstract

The distribution of intramembrane particles of nonactivated and activated human blood platelets was studied by freeze-fracture under various experimental conditions to see whether morphological evidence for a structural coupling between the platelet actomyosin system and the fibrin network in a retracting clot could be established. Membrane particles were evenly distributed in nonactivated platelets; the total number (E + P faces) was approximately 1,500/micrometers 2 of membrane, and there were two to three times more particles present on the E face than on the P face. Transformation of discoid platelets to "spiny spheres" by cooling did not change the particle distribution. Platelet activation and aggregation by serum or ADP caused no change in membrane particle density or distribution. Particle distribution was not changed in Ca2+-activated platelets fixed immediately before fibrin formation, but after fibrin formation and during clot retraction, particles were sometimes most frequent on the P face and tended to form distinct clusters, and aggregates of E face pits were observed. Blood platelets contain contractile proteins that are distinct as filaments in platelets in retracting clots. We suggest that the redistribution of particles seen in activated platelets during clot retraction reflects the esablishment of mechanical transmembrane links between the platelet actomyosin system and the fibrin net. The P-face particle clusters may represent sites of force transmission between actin filaments bonded to the inside of the membrane and the fibrin network at the outside. Thus, whereas membrane particles may not be directly involved in the attachment of actin filaments to membranes, the transmission of the force of the contractile system to an exterior substrate apparently involves the intramembrane particles.

Journal

The Journal of Cell BiologyRockefeller University Press

Published: Oct 1, 1980

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