ISSN:0953-7104    

DOI:10.3109/09537109509013255

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Collagens belong to the constituents that determine the thrombogenicity of the vessel wall. Seven genetically distinct collagens—type I, III, IV, V, VI, VIII and XIII—have been identified in the vessel wall. The interaction of platelets with collagens is a complex process since collagens are not only potent platelet agonists but also adhesive proteins. In recent years several platelet membrane glycoproteins have been shown to be involved in platelet-collagen interactions. The mechanisms of platelet-collagen interaction can be divided into primary, direct interactions and secondary, indirect interactions. A number of direct receptors for the collagens have been proposed. The glycoprotein complex Ia/IIa, also called VLA2,α2β1integrin or CD49b/CD29, meets several criteria as the major platelet receptor for different types of collagens. There is some evidence that glycoprotein IIIb, also called glycoprotein IV or CD36, functions at the earliest stages of collagen adhesion as a platelet collagen receptor. CD36 seems to be essential for type V collagen-induced platelet aggregation and adhesion. Another putative platelet-collagen receptor is P62, a glycoprotein with a molecular weight of 62 kDa under reducing conditions.

ISSN:0953-7104    

DOI:10.3109/09537109509013256

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

The level of phosphorylation of any cellular protein depends on the balance of the activities of protein kinases and protein phosphatases that act on the protein. In this study, we have characterized, in intact human blood platelets, the activity of protein phosphatase (s) that reverse the action of protein kinase C (PKC), using as a substrate, endogenous 42 kDa protein which has been previously phosphorylated by PKC. In this study 1,2-dihexanoyl-sn-glycerol (DHG) was used to stimulate PKC, diacylglycerol kinase inhibitor-R59022 was used to maintain the activity of PKC and staurosporine and okadaic acid were used to inhibit PKC and protein phosphatases respectively. Our observations indicate that: (1) protein phosphatase 1 (PP1) and/or protein phosphatase 2A (PP2A) are likely to be the enzymes that reverse the phosphorylation activity of PKC on the 42 kDa protein; (2) PP1 and/or PP2A dephosphorylate sites which have been previously phosphorylated by PKC; and (3) PP1 and/or PP2A dephosphorylate, on the 42 kDa protein, both serine and threonine residues, which have been previously phosphorylated by PKC.

ISSN:0953-7104    

DOI:10.3109/09537109509013257

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Terminal megakaryocytic development is characterized by nuclear poly ploidization, appearance of specific granules, and enhanced expression of membrane platelet glycoproteins. We utilized a human GM-CSF-dependent cell line, MB-02, which is capable of under going megakaryocytic differentiation, to examine the molecular events underlying this process. The responses of MB-02 to the protein kinase C (PKC) agonist, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were examined. GM-CSF dependent proliferation of MB-02, as measured by3H-thymidine uptake, was greater than 95% inhibited by TPA (16 nM), but was not affected by the inactive stereoisomer, 4-α-phorbol-12,13-didecanoate (4-αPDD). Transient exposure of cells to GM-CSF after growth factor deprivation led to rapid, high-level expression of normal-sized c-myc mRN A transcripts above baseline. C-myc expression was turned off by TPA (16 nM) stimulation of cells within 2-4 h. This TPA-mediated effect likely occurred at the transcriptional level since the half life of c-myc mRN A induced by GM-CSF was less than 30 min. Treatment of cells with TPA was associated with induction of c-jun and junB mRN A within 1-4 h. The protein products of these transcription factors are known to be part of the transcription factor complex Activator protein 1 (AP-1). Indeed, our data prove a rapid induction of AP-1 protein after TPA stimulation, as shown by mobility shift assays. In addition, TPA treatment resulted in expression of platelet surface glycoprotein IIb/IIIa complex (gpIIb/IIIa). These studies suggest a link between PKC stimulation by TPA and AP-1 activation with downregulation of c-myc transcription on a molecular level. At the cellular level, PKC activation was related to the acquisition of several features of the megakaryocyte development programme associated with the switch from cell proliferation to maturation.

ISSN:0953-7104    

DOI:10.3109/09537109509013258

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Washed human platelets incubated in different concentrations of fibrinogen were activated by thrombin and aggregated in the presence of Ca2+or did not aggregate when EDTA was present. They were analyzed by transmission electron microscopy and computer-aided three-dimensional reconstruction. The volumes and surface areas of the reconstructed models were calculated. The quotients of the values calculated for the whole platelet and the surface-connected canalicular system were taken as measures of the degree of surface invagination. Increasing the concentrations of fibrinogen reduced the values of the quotients indicating enhanced internalization of surface membranes, and tended to smoothen the outer surfaces to obtain spherical shapes. The invaginations are much more pronounced in platelets that did not aggregate in the presence of EDTA suggesting that aggregation fixes some membrane areas that otherwise would be redistributed to the platelet's inner compartments.

ISSN:0953-7104    

DOI:10.3109/09537109509013259

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

It has been shown that gangliosides exert an influence on serotonin (5-HT) binding and uptake by human platelets. The effect depends on ganglioside structure. In particular, GT1b increases the number of 5-HT binding sites by 40 to 60%, and GM1, GM3 and GD3 decrease it by 20 to 40%. None of the gangliosides tested influences the affinity of the 5-HT binding sites with KD= 60±10 nM. It has been found that loading platelets with GT1b increases the rate of 5-HT uptake and increases the capacity of platelets for this monoamine. It is concluded that gangliosides incorporated into platelet membranes influence the number of 5-HT binding sites on the serotonin transporter.

ISSN:0953-7104    

DOI:10.3109/09537109509013260

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0953-7104    

DOI:10.3109/09537109509013261

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Leukocyte - Depleted Blood Products Editors: T.A. Lane, G. Myllyla. (Part of Current Studies in Hematology and Blood Transfusion. Editors: J. Leikola, P. Lundsgaard- Hansen). Karger, Basel, 1994. 143 pages. Price DM206, US $137.75

ISSN:0953-7104    

DOI:10.3109/09537109509013262

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor