The cytoskeleton of the resting human blood platelet: structure of the membrane skeleton and its attachment to actin filaments.
We used high-resolution EM and immunocytochemistry in combination with different specimen preparation techniques to resolve the ultrastructure of the resting platelet cytoskeleton. The periphery of the cytoskeleton, an electron-dense subplasmalemmal region in thin section electron micrographs, is a tightly woven planar sheet composed of a spectrin-rich network whose interstices contain GPIb/IX-actin-binding protein (ABP) complexes. This membrane skeleton connects to a system of curved actin filaments (F-actin) that emanate from a central oval core of F-actin cross-linked by ABP. The predominant interaction of the radial actin filaments with the membrane skeleton is along their sides, and the strongest connection between the membrane skeleton and F-actin is via ABP-GPIb ligands, although there is evidence for spectrin attaching to the ends of the radial actin filaments as well. Since a mechanical separation of the F-actin cores and radial F-actin-GPIb-ABP complexes from the underlying spectrin-rich skeleton leads to the latter's expansion, it follows that the spectrin-based skeleton of the resting cell may be held in a compressed form by interdigitating GPIb/IX complexes which are immobilized by radial F-actin-ABP anchors.
Hartwig
J H
JH
Department of Medicine, Massachusetts General Hospital.
DeSisto
M
M
D000199:Actins / Q000097:blood* / Q000648:ultrastructure; D001792:Blood Platelets / Q000648:ultrastructure*; D003599:Cytoskeleton / Q000648:ultrastructure*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron; D010980:Platelet Membrane Glycoproteins / Q000032:analysis / Q000648:ultrastructure; D011485:Protein Binding
D000199:Actins; D010980:Platelet Membrane Glycoproteins