Role of Adenosine Diphosphate in the Aggregation of Human Blood-Platelets by Thrombin and by Fatty Acids

Nature ◽  
1964 ◽  
Vol 202 (4934) ◽  
pp. 765-768 ◽  
Author(s):  
R. J. HASLAM
Keyword(s):  
Fatty Acids ◽  
Human Blood ◽  
Blood Platelets ◽  
Adenosine Diphosphate ◽  
Human Blood Platelets

scholarly journals The synthetic RGDS peptide inhibits the binding of fibrinogen lacking intact alpha chain carboxyterminal sequences to human blood platelets

Blood ◽  
1987 ◽  
Vol 69 (3) ◽  
pp. 950-952 ◽  
Author(s):  
EI Peerschke ◽  
DK Galanakis
Keyword(s):  
Platelet Aggregation ◽  
Human Blood ◽  
Blood Platelets ◽  
Adenosine Diphosphate ◽  
Competitive Inhibitor ◽  
Minor Role ◽  
Solution Ph ◽  
Alpha Chain ◽  
A Minor ◽  
Human Blood Platelets

Abstract The alpha chain 572–574 Arg-Gly-Asp sequence of fibrinogen appears to play only a minor role in platelet aggregation based on the ability of fibrinogen preparations lacking alpha chain carboxyterminal segments to support platelet aggregation, but synthetic Arg-Gly-Asp-Ser (RGDS) peptides are capable of inhibiting platelet aggregation and fibrinogen binding. The present study thus examined the ability of RGDS peptides to inhibit platelet interactions with a plasmic degradation product of fibrinogen (8D–50) that resembles an intermediate fragment X. Gel- filtered, human blood platelets suspended in 0.01 mol/L HEPES-buffered modified Tyrode's solution, pH 7.5, were stimulated with 20 mumol/L adenosine diphosphate and the binding of 125I-labeled 8D–50 or intact fibrinogen (0.01 to 0.6 mg/mL) assessed in the presence of 0 to 117 mumol/L RGDS. The data revealed that RGDS decreased the apparent affinity of 8D–50 and intact fibrinogen for platelets but did not affect the maximum number of binding sites. RGDS thus appears to be a competitive inhibitor not only of intact fibrinogen (Ki = 12 +/- 2 mumol/L) but also of 8D–50 (Ki = 15 +/- 3 mumol/L) (mean +/- SD, n = 3).

Cytoskeletal ultrastructure and motility of cells

1980 ◽  
Vol 58 (7) ◽  
pp. 745-749 ◽  
Author(s):  
Robert Day Allen
Keyword(s):  
Human Blood ◽  
Blood Platelets ◽  
Contractile Proteins ◽  
Detailed Account ◽  
Dynamic Changes ◽  
Motile Cells ◽  
Human Blood Platelets

A brief review of the role of contractile proteins in dynamic changes in the cytoskeletons of motile cells is followed by a more detailed account of cytoskeletal ultrastructure in the motility of the giant amoeba, Chaos carolinensis and of human blood platelets.

The Use of a Chelating Ion-Exchange Resin to Evaluate the Effects of the Extracellular Calcium Concentration on Adenosine Diphosphate Induced Aggregation of Human Blood Platelets

1976 ◽  
Vol 36 (01) ◽  
pp. 208-220 ◽  
Author(s):  
Stanley Heptinstall
Keyword(s):  
Platelet Aggregation ◽  
Ion Exchange ◽  
Human Blood ◽  
Calcium Concentration ◽  
Exchange Resin ◽  
Blood Platelets ◽  
Adenosine Diphosphate ◽  
Ion Exchange Resin ◽  
Extracellular Calcium ◽  
Human Blood Platelets

Summary1. An ion-exchange resin, Chelex 100, has been used to prepare suspensions of human blood platelets in calcium and magnesium depleted plasma.2. Extracellular calcium is required for platelet aggregation when induced by adenosine diphosphate (ADP). Magnesium only supports aggregation provided that a small amount of calcium is present in the plasma.3. The extent of platelet aggregation depends upon the concentration of calcium in the plasma. There is an optimum concentration of calcium with which the maximum amount of aggregation is obtained in response to any single concentration of ADP. This optimum calcium concentration is below the physiological level. Higher calcium concentrations reduce the extent of aggregation by enhancing the rate of disaggregation and high magnesium concentrations have the same effect. It is possible that free ADP levels are reduced as a result of ADP-divalent cation complex formation.4. Platelets were found to contain 18.6 (S.D. ±1.1) × 10–6 mol Ca and 9.3 (S.D. ±1.0) × 10–6 mol Mg per 1011 cells.

Effects of Aggregating Agents, Cytochalasin B (CB) and Neuraminidase (N) on the Ultrastructure of Freeze Dried (FD) Human blood Platelets

1975 ◽  
Author(s):  
R. B. Davis
Keyword(s):  
Human Blood ◽  
Plasma Membranes ◽  
Platelet Rich Plasma ◽  
Blood Platelets ◽  
Adenosine Diphosphate ◽  
Surface Complexes ◽  
Release Reaction ◽  
Cryoprotective Agents ◽  
Freeze Dried ◽  
Human Blood Platelets

Frozen and freeze dried human blood platelets remain intact morphologically when preserved by cryoprotective agents. These studies have investigated effects of 1) the release reaction, 2) discoid stabilization by CB, and 3) N on platelet morphology in FD specimens. Platelets were collected in 1/10 volume of acid citrate and platelet rich plasma (PRP) obtained by centrifugation. Aggregating agents (adenosine diphosphate, 2 × 10-6 M, epinephrine, 5 × 10-5 M, collagen, 30 μg/ml, thrombin 0.2 U/ml) CB (25 μg/ml), trypsin (3 mgs/ml), and N (20 U/ml), then cryoprotective agents, were added. Platelets were FD and the ultrastructure examined. Aggregating agents were associated with 1 ) the appearance of amorphous electron dense material within platelets extending via channels to the exterior; 2) membranous complexes contiguous to plasma membranes; 3) numerous organelles adjacent to the plasma membrane. Platelets in artificial thrombi also showed homogeneous electron opaque areas and membrane rich surface complexes. CB caused vacuolization and previously reported concentric membranous structures were noted in trypsinized platelets. N did not prevent interplatelet bridging. In conclusion, aggregated FD platelets differ from platelets fixed by traditional means, providing morphologic support that platelet organelles and membrane systems relate structurally to the platelet exterior as well as the canalicular system to provide a catalytic lipoprotein surface during the release reaction.

scholarly journals Incorporation and turnover of eicosapentaenoic and docosahexaenoic acids in human blood platelets in vitro

1992 ◽  
Vol 281 (2) ◽  
pp. 309-316 ◽  
Author(s):  
M Croset ◽  
Y Bayon ◽  
M Lagarde
Keyword(s):  
Fatty Acids ◽  
Human Blood ◽  
Molecular Species ◽  
Blood Platelets ◽  
Blood Platelet ◽  
Total Radioactivity ◽  
Significant Release ◽  
Subsequent Activation ◽  
Human Blood Platelets

Mass changes in the incorporation of linoleic (C18:2), eicosapentaenoic (C20:5) and docosahexaenoic (C22:6) acids in human blood platelet phospholipids were induced by incubating the cells and these fatty acids complexed to albumin. The remodelling of [14C]C18:2, [14C]C20:5 and [14C]C22:6 in classes, subclasses and molecular species of platelet phospholipids was studied in resting and thrombin-stimulated cells. More than 85% of the incorporation was located in phospholipids, representing 5-fold and 2.5-fold increases in the phospholipid C20:5 and C22:6 endogenous content respectively. Thrombin stimulation induced a 30% degradation of 1-acyl-2-C20:5-glycerophosphocholine (GPC) and 1-acyl-2-C22:6-GPC, but did not induce significant release of C18:2 from 1-acyl-2-C18:2-GPC. There was no change in the [14C]fatty acid composition of 1-alkyl-2-acyl-GPC. Thrombin-dependent increases in 1-alkenyl-2-C20:5-glycerophosphoethanolamine (GPE) and 1-alkenyl-2-C22:6-GPE of 2.1-fold and 2.5-fold respectively accounted for the rise in GPE radioactivity and partly compensated for the loss of these fatty acids from 1,2-diacyl-GPC: transfer to 1-alkenyl-2-acyl-GPE was 0.4 and 1.5 nmol/10(9) platelets for C20:5 and C22:6 respectively. [14C]C20:5 and [14C]C22:6 were incorporated into six different species of 1,2-diacyl-GPC, with acylation in the major endogenous forms (C18:1 +C16:0 and C18:0 species) representing 76% and 66% respectively of the total radioactivity present in 1,2-diacyl-GPC. Stimulation by thrombin induced significant release of these fatty acids from the main molecular species of 1,2-diacyl-GPC, but significantly stimulated the synthesis of alkenyl forms of GPE containing C18:1/C22:6 +C16:0/C22:6, C18:0/C22:6 and C18:0/C20:5. C18:0/C18:2, the major endogenous C18:2 molecular species, represented only 10.5% of the incorporation; none of the [14C]C18:2 molecular species was a substrate for transfer towards 1-alkenyl-2-acyl-GPE. It is concluded that when C20:5 and C22:6, but not C18:2, are acylated in 1,2-diacyl-GPC, they participate in thrombin-dependent phospholipid remodelling, and might compete with the turnover and release of arachidonic acid from platelet phospholipids and the subsequent activation of the cells.

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