Resting platelets

CD62P or P-selectin, which is a component of the platelet a granule membrane of resting platelets. It is expressed on the platelet surface membrane only after a granule secretion. P-selectin mediates the adhesion of activated platelets to neutrophils and monocytes. 

Resting platelets exhibit a discoid shape in the circulation. This shape is maintained by the presence of circumferential coils of microtubules arranged just beneath the surface membrane. Upon platelet activation, however, microtubules de-polymerize and platelets change their shape to spheres with spiny pseudopodia containing actin filaments. 

The effect with which PPT modulate the response of platelets is also pertinent to vascular disease, in particular, thrombosis. Resting platelets inhibit the respiratory burst of neutrophils whereas thrombin-activated platelets increase the respiratory burst. Quercetin and resveratrol at picomolar concentrations attenuate this response by preserving endothelial CD39/ATP-dase," " and on present evidence (see above) such concentrations might be achieved locally following deglucuronidation at a site of inflammation. 

Bengtsson, T., Zalavary, S., Stendahl, O., and Grenegard, M. (1996) Release of oxygen metabolites from chemoattractant-stimulated neutrophils is inhibited by resting platelets Role of extracellular adenosine and actin polymerization. Blood 10,4411 1423. 

Figure 1. Scanning electronmio-ograph of resting platelets The characteristic shape of circulating discoid datelets is critical for their passage in the vessel wall with smooth blood flow (Courtesy Janies G. White, MD).

Dorahy J, Bemdt MC, Shafien DR, Bums GF CD36 is spatially associated with glycoprotein Ilb-IBa (alpha lib beta 3) on the surface of resting platelets. Biochem Biopiqrs Res Commun 218 575-581, 1996... 

Woods VL, Wolf LE, Keller DM. Resting platelets contain a substantial centrally located pool of glycoprotein Hb-HIa ccmplex whidi may be accessible to some but not other extra lular prdeins. J Biol Chem 1986 261 15242-15251. 

Plasma VWF does not interact with resting platelets unless ristocetin is added [30]. VWF... 

Circulating resting platelets do not stick to healthy endothelium or each other but if a vessel wall is... 

The incubated resting platelets fixed and adhered to mica were relatively flat and exhibit discoid shape with the width of 2.5-3.0 pm and height of 200-300 nm (Fig. 1). 

Figure 1. SFM image of human resting platelet on mica.

ADP added to resting platelets induced a sudden rise in Na uptake, an increase in platelet Na+, and a decrease in K+ (Figure 4) (37J. Earlier studies had shown that platelet water volume does not increase after ADP-induced aggregation (38), and using 6C1, we found no increase in C1 uptake (37). An uptake of Na+ was not seen after GDP addition. 

In healthy blood vessels, resting platelets do not adhere to the non-thrombogenic surface of intact endothelium. However, platelets can adhere... 

Immunoblotting-based experiments using an anti-phosphotyrosine antibody showed that incubation of platelets with ajoene enhanced the phosphorylation of at least four proteins (estimated molecular weights 76, 80, 84 and 120 kDa), both in resting platelets and in platelets subsequently stimulated with thrombin (0.1 U/ml). This effect was both dose- and incubation-time-dependent. High concentrations of ajoene (50 pM) or long periods of incubation (10 min) led to nonselective hyperphosphorylation of numerous proteins. Also, protein tyrosine phosphatase activity was inhibited when platelets were incubated with ajoene before lysis, but not when ajoene was added to lysates of platelets which had not been pre-exposed to ajoene [99],... 

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