Platelet clearance has already been studied in physiological and pathological conditions and shown its occurrence mainly in the liver and the spleen. It is still not clear what mechanisms are responsible for recognition and removal of either aged or damaged platelets by the scavenging system. So study of the clearance mechanism will be useful to prolong the survival time of platelets in vivo. And it may be related to a new strategy to store platelets. This article focuses on the advances in studies of the clearance mechanism of transfused platelet concentrates, including roles of P-selectin, GPI balpha and its receptor Mac-1 in platelet clearance, and effect of endogenous metalloproteinase in platelet clearance.
Blood Platelets ; physiology ; Blood Preservation ; Cellular Senescence ; Humans ; Macrophage-1 Antigen ; physiology ; Metalloproteases ; physiology ; P-Selectin ; physiology ; Platelet Activation ; Platelet Glycoprotein GPIb-IX Complex ; physiology ; Platelet Transfusion

In pancreatic acinar cells Ca(2+)-dependent secretagogues promote the fusion of zymogen granules (ZG) with the apical plasma membrane (PM) and exocytosis of digestive enzymes. In addition to exocytotic fusion complexes between SNARE proteins in the ZG membrane (ZGM) and the apical PM, enzyme secretion elicited by Ca(2+)-dependent secretagogues requires cytosolic Cl and K+ and is inhibited by blockers of Cl- and K+-channels. We have identified a Cl-conductance activated by ATP, and a K+-conductance (with properties similar to ATP-sensitive K+-channels), regulated by the granule matrix protein Zg-16p in the ZGM. Both conductances are inversely regulated by a 65-kD mdr1 gene product. We have also identified a novel Ca(2+)-activated anion conductance in ZGM, the Ca(2+)-sensitivity of which increases 50-fold when Cl is replaced by 1. This conductance is blocked by micromolar H2-DIDS or DTT, reminiscent of a family of epithelial Ca(2+)-activated Cl -channels (CaCC). Expression of a CaCC in exocrine pancreas has been confirmed by RT-PCR analysis, and by immunoblotting and immunogold labeling of ZG membranes. These data suggest that ion channels in the ZGM are essential elements in pancreatic exocytosis.
Animal ; Chloride Channels/metabolism* ; Chloride Channels/genetics ; Exocytosis/physiology* ; Gene Expression/physiology ; P-Glycoprotein/metabolism ; P-Glycoprotein/genetics ; Pancreas/secretion* ; Pancreas/cytology ; Potassium Channels/metabolism* ; Potassium Channels/genetics ; Secretory Vesicles/secretion ; Secretory Vesicles/metabolism* ; Support, U.S. Gov't, P.H.S.

A depressed level of natural killer (NK) activity is one of the various immunologic abnormalities in human immunodeficiency virus (HIV) infection. Interleukin-15 (IL-15), an immunotherapeutic candidate in HIV infection, increases NK activity and induces the excretion of CC-chemokines from divergent immune cells, but the mechanisms of NK activity enhancement by IL-15 stimulation is not clearly established in HIV infection. This study examined whether CC-chemokines, which are known to increase NK activity, are secreted adequately in HIV-infected individuals, and also investigated whether P-glycoprotein is involved in NK activity enhancement after IL-15 administration. NK activity increased with IL-15 stimulation in NK cells of HIV-infected individuals, as it does in normal NK cells. IL-15 stimulates NK cells to secrete CC-chemokines, such as, macrophage inflammatory protein-1alpha (MIP-1alpha), macrophage chemotactic protein-1alpha (MCP-1alpha) and regulated upon activation, normal T cells expressed and secreted (RANTES) in both HIV-infected individuals and controls with no significant difference. P-glycoprotein expression and function is decreased in HIV-infected individuals and restored only in NK cells of HIV-infected individuals after IL-15 stimulation. P-glycoprotein may play a role in the mechanism of increased NK cell activity in HIV-infected individuals after IL-15 stimulation.
HIV Infections/physiopathology* ; HIV Infections/pathology ; Human ; Interleukin-15/pharmacology* ; Killer Cells, Natural/physiology* ; Killer Cells, Natural/drug effects* ; P-Glycoprotein/physiology* ; Recombinant Proteins/pharmacology

This study was designed to compare the effects of protease-activated receptor 1 (PAR-1) and protease-activated receptor 4 (PAR-4) to the expression of platelet surface GPIbalpha and cytoskeleton reorganization, then to investigate the role of PARs in platelet signal transmission. PAR1 (25 micromol/L) and PAR4 (250 micromol/L) were used to stimulate platelet at different time points (0 - 60 minutes), and the platelet surface GPIbalpha, actin and myosin and P-selectin were detected with flow cytometry, the alteration of GPIbalpha, actin and myosin in cytoskeleton was compared by Western blot, the membrane cytoskeleton followed GPIbalpha immunoprecipitation was analyzed. The results showed that an increase of P-selectin and reversible decrease of GPIbalpha expression were obtained after platelet activation by PAR1 o r PAR4, and a different kinetics of redistribution of GPIbalpha was found for the two peptides all over the time course (P < 0.05). PAR1 acted more potently and rapidly than PAR4, but the effect of PAR4 persisted longer in the course of platelet activation. Meanwhile, there was a transient change of actin, myosin and GPIbalpha in cytoskeleton proteins. Similar redistribution was also found in GPIbalpha/myosin and GPIbalpha/actin association. It is concluded that PAR1 and PAR4 possess an important role in platelet signal transmission. Either of the receptors can mediate platelet activation and GPIbalpha redistribution, which is correlated with cytoskeleton reorganization. PAR1 acts more rapidly, and effect of PAR4 persists longer.
Cytoskeleton ; chemistry ; Flow Cytometry ; Humans ; Myosins ; analysis ; P-Selectin ; analysis ; Platelet Activation ; Platelet Glycoprotein GPIb-IX Complex ; Receptor, PAR-1 ; physiology ; Receptors, Thrombin ; physiology

It is generally accepted that tissue factor plays an important role in coagulation and intravascular thrombus formation. Tissue factor is not only found primarily on the surface of certain cells that are located outside the vasculature, but also found in circulating cells. Monocyte express tissue factor induced by endotoxin. Recently, many researches indicate that P-selectin, CD40 ligand and GPIIb/IIIa receptor of platelet can also affect expression of tissue factor by monocyters. In addition, a lot of studies showed that tissue factor exist in the circulation including contained platelet. Tissue factor in the platelet releases under certain condition, and initiates coagulation. In this review the relation between platelet and tissue factor was elaborated.
Blood Platelets ; drug effects ; metabolism ; physiology ; CD40 Ligand ; physiology ; Humans ; Monocytes ; drug effects ; metabolism ; P-Selectin ; physiology ; Peptides ; pharmacology ; Platelet Glycoprotein GPIIb-IIIa Complex ; physiology ; Thromboplastin ; biosynthesis ; drug effects ; physiology

MDR1 promoter has been shown to contain heat shock elements (HSE), and it has been reported that FM3A/M and P388/M MDR cells show a constitutively activated heat shock factor (HSF), suggesting that HSF might be an important target for reversing the multidrug resistance. Therefore, it was examined whether quercetin, which has been shown to interfere with the formation of the complex between HSE and HSF, and to downregulate the level of HSF1, can sensitize MDR cells against anticancer drugs by inhibition of HSF DNA-binding activity. In this study, quercetin appeared to inhibit the constitutive HSF DNA-binding activity and the sodium arsenite-induced HSF DNA-binding activity in the MDR cells. The basal and sodium arsenite-induced MDRCAT activities were remarkably suppressed by the treatment of quercetin. These results were well consistent with the finding that the treatment of quercetin decreased the expression level of P-gp, MDR1 gene product, in dose-dependent manner, and markedly increased the sensitivity of MDR cells to vincristine or vinblastine. These results suggest that quercetin can decrease the expression of P-gp via inhibition of HSF DNA-binding activity, and might be useful as a chemosensitizer in MDR cells.
Animal ; Antineoplastic Agents/pharmacology ; Arsenites/pharmacology ; Carcinoma/drug therapy ; Drug Resistance, Multiple/physiology* ; Drug Resistance, Neoplasm/physiology ; Heat-Shock Proteins/metabolism ; Heat-Shock Proteins/drug effects* ; Heat-Shock Proteins/antagonists & inhibitors ; Leukemia, Experimental/drug therapy ; Mice ; P-Glycoprotein/genetics ; P-Glycoprotein/drug effects ; Quercetin/pharmacology* ; Sodium Compounds/pharmacology ; Tumor Cells, Cultured ; Vinblastine/pharmacology ; Vincristine/pharmacology

<p>OBJECTIVETo detect the redistribution of platelet surface glycoprotein (GP)Ib alpha and cytoskeleton reorganization in the course of thrombin receptor activation, and investigate the mechanism of GPIb alpha re-translocation and the role of thrombin receptors in platelet signal transduction.p><p>METHODSThe thrombin receptor activating peptide (PAR1-AP, TRAP) was used for stimulating platelet at different time points (0 - 60 min), then the platelet surface GPIb alpha and P-selectin were examined with flow cytometry, and the alterations of GPIb alpha, actin and myosin were analyzed in cytoskeleton by Western blot and GPIb alpha immunoprecipitation. Cytochalasin D and/or Apyrase VII were used for investigating their inhibitory effect on platelet activation.p><p>RESULTSAn increase of P-selectin and reversible internalization of GPIb alpha were observed within platelets upon TRAP activation, and transient changes of actin, myosin and GPIb alpha/myosin, GPIb alpha/actin association were also found in this course. These changes were apparently blocked by cytochalasin D, which inhibited the incorporation of GPIb alpha, actin and myosin into cytoskeleton. Apyrase VII had a weak effect on GPIb alpha internalization, although it accelerated the return of GPIb alpha to platelet surface. In addition, Apyrase VII also quickened the GPIb alpha disappearance in cytoskeleton and the dissociation of GPIb/myosin or GPIb/actin during activation.p><p>CONCLUSIONThrombin receptor activation takes part in platelet signal transduction, inducing a reversible redistribution of GPIb alpha. This process is related to cytoskeleton reorganisation and ADP.p>
Actins ; metabolism ; Blood Platelets ; cytology ; drug effects ; metabolism ; Blotting, Western ; Cells, Cultured ; Cytoskeleton ; metabolism ; Humans ; Myosins ; metabolism ; P-Selectin ; metabolism ; Peptide Fragments ; pharmacology ; Platelet Activation ; drug effects ; physiology ; Platelet Glycoprotein GPIb-IX Complex ; metabolism ; Receptors, Thrombin ; metabolism ; physiology

To investigate the pathophysiological mechanisms for platelet-neutrophils cross talk mediated by platelet-activating factor (PAF) and to lay a foundation for clinical application, ginkgolides B (GB), a PAF receptor antagonist, was added in the whole blood to block the effects of PAF on activation of platelet-neutrophil; PAF and ADP were respectively added in the whole blood to monitor the expression of CD62P on platelet by flow cytometry; PAF and ADP were added in the whole blood to monitor the expression of CD11b on neutrophil by flow cytometry; PAF and ADP were added in the whole blood to monitor the platelet-leucocyte aggregates (PLA) which were PLA in the total leucocyte population (PLA/L) and the mean fluorescence intensity (MFI) of CD42b. Outcomes were analyzed by t-test, and the differences were statistically significant (P < 0.05). The results showed that the expression of CD62P on platelats, the expression of CD11b on neutrophils and PLA formation were all increased by PAF and ADP; the PAF receptor antagonists (GB) could obviously inhibit the expression of CD62P, CD11b and PLA formation induced by PAF, but could not completely inhibit the activation of platelet and neutrophil, and the platelet-neutrophil cross talk; GB could inhibit the expression of CD62P and CD11b induced by ADP, but could not conpletely inhibit the activation of platelet and neutrophli; GB could not obviously inhibit the platelet-leucocyte aggregates mediated by ADP. It is concluded that the multiligand-receptor systems involved in PLA formation and platelet-netrophils cross talk seem to be regulated by complex mechanisms; the PAF receptor antagonists (GB) obviously inhibit the effect of PAF, and may be widely utilized in the therapy of thrombosis and inflammation.
Adenosine Diphosphate ; pharmacology ; Adult ; Blood Platelets ; cytology ; drug effects ; physiology ; CD11b Antigen ; blood ; Cell Adhesion ; drug effects ; physiology ; Cell Communication ; drug effects ; physiology ; Female ; Flow Cytometry ; Ginkgolides ; pharmacology ; Humans ; Male ; Middle Aged ; Neutrophils ; cytology ; drug effects ; physiology ; P-Selectin ; blood ; Platelet Activating Factor ; pharmacology ; Platelet Activation ; drug effects ; Platelet Glycoprotein GPIb-IX Complex ; analysis ; Platelet Membrane Glycoproteins ; antagonists & inhibitors ; physiology ; Receptors, G-Protein-Coupled ; antagonists & inhibitors ; physiology

To investigate the changes of platelet activated state and platelet activated function by trace whole blood flow cytometry (FCM), and to explore the mechanism of hemorrhage and infiltration in adults with acute leukemia, the expression percentage and changes of these expressions of CD62p and PAC-1 on platelet surface were determined by FCM of trace whole blood after platelet activated by ADP in patients with new diagnosed AL (group I), complete remission (CR, group II) and continuously complete remission (CCR, group III). Healthy adults were used as control group. The result showed that the expression of CD62p in group I and II was higher than that in control group, before and after platelet activated by ADP (P < 0.01). The expression of PAC-1 in group I was higher than that in control group (P < 0.01), the expression of PAC-1 in group II was lower than that in control group (P > 0.01), There was no significant difference in expression of CD62p and PAC-1 between group III and control group (P > 0.01), and no significant difference was found between AL group with megakaryocyte malignant pathological changes and AL group without megakaryocyte malignant pathological changes before platelet activated by ADP (P > 0.01). After platelet activated by ADP, the expression of PAC-1 in the former was lower than that in the latter (P < 0.01). It is concluded that (1) high level activated platelet in peripheral blood of AL patients show that interaction between activated platelet and leukemia cells can be one of reason resulting in widespread hemorrhage and infiltration AL patiens; (2) the decrease of number and activted function of platelet at the first stage of AL patients may be caused by malignant hyperplasia of leukemia cells and damage of megakaryopoiesis in bone marrow.
Acute Disease ; Adenosine Diphosphate ; pharmacology ; Adolescent ; Adult ; Aged ; Blood Platelets ; cytology ; metabolism ; Cell Membrane ; drug effects ; metabolism ; Female ; Flow Cytometry ; Humans ; Leukemia ; blood ; pathology ; Male ; Middle Aged ; P-Selectin ; biosynthesis ; Platelet Activation ; drug effects ; physiology ; Platelet Glycoprotein GPIIb-IIIa Complex ; biosynthesis