摘要:

Palmitoylation as incorporation of [3H] palmitic acid into proteins occurred in platelets as in other cell systems. The linkage of palmitic acid to platelet proteins was stable to SDS and organic solvents but was sensitive to hydroxylamine, consistent with oxyester or thioester bond(s). Non-reduced SDS PAGE analysis revealed that the most prominantly labelled proteins were a quadruplet of proteins of 30–38 kDa. Under reducing conditions, these proteins appeared as a doublet of 38 kDa proteins. Thrombin or PMA enhanced the incorporation of label into these proteins, suggesting the involvement of palmitoylation in platelet activation. In prelabelled platelets, A23187 led to a E-64d-sensitive decrease of label associated with a 35 kDa protein while PMA caused a stuarosporine-sensitive shift of the same protein in a non-reduced gel. Some of the palmitoylated proteins were associated with the cytoskeleton. Thrombin appeared to have different effects on these labelled cytoskeletal proteins. While the identity of most of the palmitoylated platelet proteins remains unknown, a few palmitoylated proteins have been identified to be CD9, glycoproteins IIIa, Ib and IX.

ISSN:0953-7104    

DOI:10.3109/09537109409005515

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

Under physiological conditions human blood platelets play a beneficial role in fibrinolysis and regulate the balance with prostacyclin and other factors derived from the endothelium. In response to endothelial injury, adherence of platelets to the denuded arterial surface, platelet aggregation, release of mitogens and subsequent cell proliferation characterize early fibrous plaque lesions.‘Native’atherogenic plasma lipoproteins which are abundant in hypercholesterolemia have been found to play a subtle role in the development of atherosclerosis. In addition, lipoproteins modulate platelet function and alter the susceptibility of platelets to different stimulating agents. The properties of‘modified’atherogenic lipoproteins also seem to be well documented with respect to atherogenesis. After uptake by macrophages, modified atherogenic plasma lipoproteins are thought to contribute to formation of fatty streak lesions. On the other hand, modified atherogenic lipoproteins may directly promote endothelial injury and thus favour enhanced endothelial-platelet interactions. However, the direct effects of modified atherogenic lipoproteins on platelet function have not been revealed in detail. Recent findings have documented that activated platelets themselves may promote modification of atherogenic plasma lipoproteins and thus contribute to enhanced foam cell formation. Therefore stimulation of thrombocytes, and their interaction with native and modified lipoproteins must be considered an important factor in the current concept of atherogenesis.

ISSN:0953-7104    

DOI:10.3109/09537109409005516

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

Adding adenosine diphosphate (ADP) to platelet-rich plasma (PRP) results in a fall in the level of platelet monomeric globular (G)-actin indicative of actin polymerization. There is an immediate fall in G-actin associated with shape change which is reversible, and a second phase or sustained response associated with second phase or irreversible aggregation. Previous studies suggested that platelet aggregation is a prerequisite for second phase or sustained actin polymerization.Here we have examined further the relationship between platelet aggregation and actin polymerization in ADP-stimulated platelets by studying the effects of M148, a monoclonal antibody that inhibits aggregation by combining with the glycoprotein (Gp) IIb/IIIa complex, and the effects of dissociating GpIIb/IIIa by incubating platelets with EGTA at 37°C. We also assessed the contribution of thromboxane A2(TXA2) by inhibiting its synthesis with aspirin.The results show that GpIIb/IIIa is involved in mediating the second phase or sustained actin polymerization that occurs after activating platelets with ADP and confirm the requirement for platelet aggregation. TXA2synthesis is not required for second phase or sustained actin polymerization, but TXA2contributes to second phase or sustained actin polymerization, probably via promotion of further platelet-platelet contact.

ISSN:0953-7104    

DOI:10.3109/09537109409005517

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

Pregnancy is marked by the placental production of vasopressinase, an enzyme which accelerates the metabolic clearance of arginine vasopressin (AVP), and serum vasopressinase is reported to be abnormally elevated in hypertensive pregnancy. Since platelet AVP binding capacity is influenced by the plasma AVP concentration, we sought to determine whether alterations in vasopressinase and AVP concentrations affect platelet responsiveness to AVP in normotensive and hypertensive pregnancy. Four groups of 10 women were studied: non-pregnant subjects, normotensive pregnancy, hypertensive pregnancy, and pre-eclampsia (PE). AVP-induced platelet aggregation was measured turbidometrically, serum vasopressinase by chromogenic assay and plasma AVP by radioimmunoassay. Platelet responses to AVP were similar in all groups, as were plasma concentrations of AVP. Vasopressinase was raised in all pregnant patients compared with non-pregnant subjects, and levels were significantly higher in pregnancy-induced hypertension than in either the normotensive or PE groups (p<0.05). No significant correlation was observed between platelet responsiveness to AVP and circulating concentrations of either AVP or vasopressinase. Thus circulating vasopressinase is increased in pregnancy and abnormally so in hypertensive pregnancy. This does not, however, appear to influence ex vivo platelet responsiveness to AVP.

ISSN:0953-7104    

DOI:10.3109/09537109409005518

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

A major challenge in the use of artificial materials for implant devices, artificial organs, and extra-corporeal circulation systems, is the adhesion of platelets and the subsequent formation of platelet aggregates on the non-biological surface. The mechanism of platelet attachment to artificial surfaces is not completely understood. Using an enzyme immunoassay, we examined platelet deposition to the polystyrene plastic of microtiter plate wells under static conditions. Following thrombin stimulation, platelets adhered to the wells. This adhesion process was suppressible by the use of different substances known to interfere with the function of the platelet surface glycoprotein IIb/IIIa complex (GPIIb/IIIa). The substances we used wereethylenediaminetetraacetic acid (EDTA), tetrapeptide RGDS (Arg-Gly-Asp-Ser), and a monoclonal antibody directed against the IIIa moiety of the GPIIb/IIIa complex. Our results indicate that the GPIIb/IIIa complex is the platelet receptor which mediates platelet adhesion to polystyrene plastic under such static conditions. The GPIIb/IIIa complex should consequently be regarded as a multifunctional platelet regulator which, depending on the circumstances, may support platelet adhesion as well as platelet aggregation. By contrast, a monoclonal antibody directed against the platelet surface glycoprotein complex Ib/IX (GPIb/IX) did not under the same static conditions inhibit platelet deposition to the polystyrene plastic.In the microtiter wells, platelet alpha-granular proteins were detected either on the surface of adherent platelets or, when platelet deposition was inhibited by EDTA directly on the polystyrene plastic. In the latter case, fibrinogen and thrombospondin were definitely the dominating proteins. The presence of platelet-derived proteins in the microtiter wells significantly enhanced the adhesion of thrombin-stimulated platelets but not of non-stimulated platelets.

ISSN:0953-7104    

DOI:10.3109/09537109409005519

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

Platelet-derived growth factor (PDGF) andβ-thromboglobulin (β-TG) are released from platelet alpha-granules during platelet activation. PDGF is a potent chemoattractant and mitogen for human vascular smooth muscle cells, and may be important in the development of late restenosis following angioplasty and in atherogenesis. In recent studies, where PDGF release into serum was evaluated indirectly by measuring3H-thymidine incorporation into fibroblasts, it was reported that the antiplatelet drug dipyridamole (DPM) decreased serum levels of PDGF. Such selective inhibition of the PDGF-release would have potential important implications for patients with atherosclerosis and for patients undergoing angioplasty. We therefore measured platelet content of PDGF andβ-TG as well as platelet release of PDGF using a newly developed radioimmunoassay in healthy volunteers before and immediately after ingestion of DPM 100 mg t.i.d. for 3 days. We found no significant differences in platelet content of PDGF orβ-TG before and after DPM. PDGF release from platelets isolated from plasma by gel filtration and stimulated with thrombin as well as platelet release of PDGF into serum was also unaffected by DPM. In conclusion, treatment with DPM does not affect platelet content of PDGF orβ-TG. The treatment did not inhibit the platelet-release of PDGF as previously reported, neither via direct effects on platelets nor on inhibitory plasma components. DPM may, however, inhibit3H-thymidine incorporation into fibroblasts.

ISSN:0953-7104    

DOI:10.3109/09537109409005520

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

Shedding of cytoplasm from circulating megakaryocytes (MKs) within the pulmonary vasculature suggests the lungs are an important site for normal platelet production. Fetal lungs receive only a minor fraction of the circulating blood volume. The placenta may act as a site for intrauterine platelet formation. Isolation of MKs from fetal vessels within the placenta has not been previously reported. Immediately after delivery, 3 human placentae were subjected to forward and retrograde perfusion across the placental capillary bed on the fetal side. MKs in perfusates were harvested by‘whole blood filtration’and identified by morphological and immunochemical methods. All perfusates yielded MKs. Qualitatively MKs with copious cytoplasm were more commonly found in perfusates collected from fetal arteries compared with those from fetal veins. This is consistent with filtration of MKs and fragmentation of their cytoplasm within the placental microcirculation to produce platelets. Perfusion of human placentae followed by filtration of perfusates is a useful technique for harvesting fetal MKs and permitting further elucidation of their physiological role.

ISSN:0953-7104    

DOI:10.3109/09537109409005521

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

There is still disagreement about the presence of receptors for low density lipoproteins (LDL) in human platelets. Therefore, washed human platelets in suspension were incubated with gold-labelled LDL, and the binding sites for LDL were revealed by transmission electron microscopy on ultrathin sections and on surface replicas. The LDL-gold complexes bound to the platelet membrane and appeared in the open canalicular system. Gold particles were also found within the coated vesicles. The predominant labelling pattern, showed by the surface replicas, was that of scattered single gold particles randomly distributed over the platelet surface. Some small clusters of gold particles were also observed, uniformly distributed between the individual particles. Competitive experiments using an excess of unlabelled LDL suggested that the binding was due to specific binding sites for LDL on the platelet membrane, possibly the LDL receptor. However, the binding sites are not expected to be the classical apolipoprotein B/E receptor, since the binding was inhibited by preincubating the platelets with anti-glycoprotein IIb-IIIa.

ISSN:0953-7104    

DOI:10.3109/09537109409005522

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor