Three‐dimensional organization of the platelet cytoskeleton during adhesion in vitro: Observations on human and nonhuman primate cells

Abstract

Adhesion of platelets in vitro resulted in rapid polymerization of the amorphous cytoplasmic ground substance into an organized cytoskeletai superstructure. This cytoskeleton, characterized through the use of whole-mount and stereo (3-D), high-voltage microscopy in conjunction with morphometrics and cytochemistry, comprised four major size classes of filaments organized in distinctive zones. The central matrix, or granulomere, at the center of the cell mass, was an ill-defined meshwork of 80-100-A filaments which enshrouded granules, dense bodies, and elements of the dense tubular system as identified through peroxidase cytochemistry. Demarcating this central matrix was a trubeculur zune containing 30-50, 80-100, and 150-170A filaments in an open.and rigid-appearing lattice. Circumscribing the trabecular zone and extending to the margins of the hyalomere was the third region, the peripheral web, in which 70-A filaments were arranged in a tight honeycomb lattice. This organizational pattern was retained in cytoskeletons prepared by Triton x-100 extraction of the adherent cells, and was observed in basally located cells of aggregates which formed subsequent to adhesion. Our observations are consistent with biochemical studies of cytoskeletons prepared from suspended platelets and suggest a contractile protein composition for the superstructure during adhesion.

Distribution and movement of membrane‐associated platelet glycoproteins: Use of colloidal gold with correlative video‐enhanced light microscopy, low‐voltage high‐resolution scanning electron microscopy, and high‐voltage transmission electron microscopy

“…This sequence of adhesion and spreading involves a morphologic change from a disc shape through spherical and several pseudopodial stages and finally culminates in a flattened, circular, fully spread stage. We, and others, have shown with correlative SEM and HVEM that major cytoskeletal reorganization occurs concomitant with this shape change process Albrecht and Lewis, 1982;Goodman et al, 198913;Lewis, 1983Lewis, , 1984Nachmias et al, 1979;White, 1987;Mosher et al, 1985). Briefly, discoid forms have no or little polymerized actin, but do possess a peripheral microtubular band.…”

Animal models for the assessment of novel vascular conduits

“…Baboons exhibit a high degree of genetic similarity with humans, 61 so it is unsurprising that the hemostatic system of humans is most closely approximated by the baboon and other Old World primates. [62][63][64] In a comparative study, Feingold et al 65 found that baboons demonstrate a similar fibrinogen level and thrombin time to humans, and the prothrombin time (PT) and activated partial thromboplastin time (APTT) are only slightly increased, whereas they are significantly shorter in canines. Baboon factor VIII activity is also similar to humans, and factor VIII antigen cross-reacts with human factor VIII antibodies.…”

Platelet adhesion: Structural and functional diversity of short dystrophin and utrophins in the formation of dystrophinassociated-protein complexes related to actin dynamics

“…Platelets are cellfragmentswith striking dynamic propertiesinvolved in clot formation after blood vesseli njury. Platelets becomeactivatedafter exposure to several agonistssuch as adenosine diphosphate (ADP), collagen, thrombin or after adhesion to surfaces such as glass (1).During activation, platelets undergo dramatic shape changes from discoid shape in the blood circulation to arounded shape projecting filopodia and to aspread shape associated with aconsequent increase of the plateletsurface. Thesemodifications of shape do not onlyfacilitate efficient adhesion to the substrate, butalso the aggregation to otherplatelets (2,3).…”