Platelet activation begins with conversion of a quiescent, disc-shaped cell to a more-rounded form possessing multiple pseudopodia. Secretion of granule contents active in hemostasis takes place, and the platelets aggregate to form white thrombi. These processes must occur within seconds or fractions of a second to ensure efficient hemostasis in rapidly-flowing blood. Present research is only beginning to consider the initiation and regulation of these important early events. Some evidence exists for activation of nucleotide, lipid and protein metabolism within 5 seconds of platelet activation. However, partly because of methodology, knowledge is limited and sometimes contradictory when correlating chemical and functional events. Our proposed research is therefore directed to understanding the mechanisms by which platelet function is initiated, especially in the critical first 5 seconds. Platelet function will be evaluated by new quenched-flow techniques which provide control of second or sub-second reaction times.
Aims are to assess the significance of the phosphatidyl inositol (PI) cycle in normal platelet activation, and whether fibrinogen interaction with platelets occurs in primary aggregation via the glycoproteins GPIIb/IIIa, or whether this takes place much later during aggregate stabilization. The role of inositol trisphosphate (1P3) as a product of the PI cycle will be evaluated, especially in terms of its ability to increase intracellular calcium levels. Specific inhibitors such as lithium or colchicine will be employed to test effects of regulation of the cycle on efficiency of platelet function. Formation of certain phosphoproteins will also be evaluated. Monoclonal antibodies to GPIIb/IIIa will be prepared and used to test specific association of bound fibrinogen to these glycoproteins. The kinetics and nature of fibrinogen association with platelets during the first few seconds of their aggregation and shape change will be measuerd, and compared to much later when aggregate stabilization occurs.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL027014-05
Application #
3338862
Study Section
Hematology Subcommittee 2 (HEM)
Project Start
1981-09-01
Project End
1988-03-31
Budget Start
1986-04-01
Budget End
1987-03-31
Support Year
5
Fiscal Year
1986
Total Cost
Indirect Cost
Name
University of Virginia
Department
Type
Schools of Medicine
DUNS #
001910777
City
Charlottesville
State
VA
Country
United States
Zip Code
22904
Polanowska-Grabowska, R; Gear, A R (2000) Heat-shock proteins and platelet function. Platelets 11:22-Jun
Polanowska-Grabowska, R; Gear, A R (1999) Activation of protein kinase C is required for the stable attachment of adherent platelets to collagen but is not needed for the initial rapid adhesion under flow conditions. Arterioscler Thromb Vasc Biol 19:3044-54
Simon Jr, C G; Holloway, P W; Gear, A R (1999) Exchange of C(16)-ceramide between phospholipid vesicles. Biochemistry 38:14676-82
Simon Jr, C G; Gear, A R (1999) Sphingolipid metabolism during human platelet activation. Thromb Res 94:13-23
Polanowska-Grabowska, R; Simon Jr, C G; Gear, A R (1999) Platelet adhesion to collagen type I, collagen type IV, von Willebrand factor, fibronectin, laminin and fibrinogen: rapid kinetics under shear. Thromb Haemost 81:118-23
Simon Jr, C G; Chatterjee, S; Gear, A R (1998) Sphingomyelinase activity in human platelets. Thromb Res 90:155-61
Simon Jr, C G; Gear, A R (1998) Membrane-destabilizing properties of C2-ceramide may be responsible for its ability to inhibit platelet aggregation. Biochemistry 37:2059-69
Polanowska-Grabowska, R; Simon Jr, C G; Falchetto, R et al. (1997) Platelet adhesion to collagen under flow causes dissociation of a phosphoprotein complex of heat-shock proteins and protein phosphatase 1. Blood 90:1516-26
Dittmar, S; Polanowska-Grabowska, R; Gear, A R (1994) Platelet adhesion to collagen under flow conditions in diabetes mellitus. Thromb Res 74:273-83
Polanowska-Grabowska, R; Gear, A R (1994) Role of cyclic nucleotides in rapid platelet adhesion to collagen. Blood 83:2508-15

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