Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intracellular Ca2+ mobilization in the resting platelets undergoing Ca2+ influx and in the activated platelets stimulated by thrombin and phorbol ester (TPA) was investigated by measuring cytosolic Ca2+ concentration: [Ca2+]cyt (fura-2, aequorin), membrane-bound Ca2+ (chlortetracycline) and Ca2+ flux across the plasma membrane (45Ca2+ tracer). Some modified methods employed in this study concerning 45Ca2+ flux measurement and aequorin loading into platelets were very useful to elucidate the details of platelet Ca2+ mobilization in the combination with other Ca2+ assay methods. These combined and integrated assays on platelet Ca2+ showed some new interesting findings as follows; (1) The difference of the obtained values of [Ca2+]cyt and of the reaction pattern between fura-2 and aequorin method was responsible to the difference of the distribution of probe molecules in platelet. This was confirmed by the higher sensitivity of aequorin molecules to [Ca2+]cyt elevation induced by Ca2+ influx than by that of fura-2 molecules in thrombin- and TPA-activated platelets. (2) The membrane-bound Ca2+ release in activated platelets was found to be another intracellular Ca2+ movement distinct from organelle Ca2+ release and CTC molecules not to bind to the organelle membranes. (3) The plasma membrane Ca2+ pump was found to exist in both unstimulated platelets and stimulated platelets suggested by its specific time course of 45Ca2+ binding and [Ca2+]cyt increase in platelets. (4) There existed biphasic increase of [Ca2+]cyt in thrombin-stimulated platelets consisted of biphasic Ca2+ influx and biphasic intracellular Ca2+ release with alternating point at 10 seconds after activation. The initial changes seemed to be correlated with receptor operated Ca2+ channel and receptor-linked phospholipase C activation respectively, while both second phase increase seemed to be correlated with the plasma membrane phospholipid metabolisms evoked by phospholipase A2 activation.
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PMID:[Significance of multiple analysis of platelet Ca2+ mobilization by using some available methods measuring cytosolic Ca2+ concentration, membrane-bound Ca2+ and Ca2+ flux across the plasma membrane]. 276 17

Generation of reactive oxygen species (ROS) by platelets was detected by a cyano-tetrazolium dye (CTC) which forms fluorescent formazan on the cell surface upon reduction. Fluorescence was quantitated by a densitometric device. Resting platelets in plasma produced significant fluorescence (P < 0.0001), and addition of thrombin enhanced the fluorescence of the coagulated platelet mass even further (by 2 h, a 6- and 8-fold increase over fluorescence of platelet-free plasma was measured, respectively). Blood containing CTC was perfused through a glass capillary tubing and the action of shear forces resulted in the formation of an occlusive platelet thrombus. Such thrombi (formed either from whole blood or platelet-rich plasma) were intensely fluorescent, indicating formation of ROS in the platelet mass (a 10- and 8-fold increase in fluorescence over coagulated plasma, respectively). Lipid peroxide content of resting platelets in platelet-rich plasma was doubled over 24 h storage, while addition of thrombin caused a 7.4-fold increase (P < 0.0001) of lipid peroxides in the retracted platelet-rich plasma-clot. Transition metal chelator and antioxidant prevented lipid peroxidation by platelets in response to thrombin. Thrombin activation of (washed) platelets in plasma-free medium caused only 1.4-fold increase in oxidation of added low density lipoprotein (LDL). In contrast, thrombin activation of platelets suspended in de-lipidated autologous plasma resulted in a 5.25-fold increase (P < 0.0001) in LDL oxidation. Generation of ROS and lipid peroxides by platelets can be an important mechanism through which thrombotic events contribute to atherogenesis.
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PMID:Lipid peroxidation by activated platelets: a possible link between thrombosis and atherogenesis. 766 82

Bernard-Soulier syndrome (BSS) is a rare hereditary bleeding disorder and macrothrombocytopenia which is caused by a defect in the platelet glycoprotein Ib/IX/V (GP Ib/IX/V) complex, the receptor for von Willebrand factor and thrombin. Here we report the molecular basis of the classical form of BSS in two unrelated Finnish patients, both with a life-long history of severe bleeding. Flow cytometry and immunoblotting showed no expression of GP Ib/IX, GP Ib alpha, GP Ib beta or GP IX (less than 10%) in the patients' platelets. No expression of GP V (< 10%) was observed in propositus 1, but a residual amount was found in propositus 2 (24%). DNA sequencing analysis revealed that propositus 1 was compound heterozygous for a two-base-pair deletion at Tyr505(TAT) and a point mutation Leu129(CTC)Pro(CCC) in the GP Ib alpha gene. Propositus 2 was homozygous for the Tyr505(TAT) deletion. The nine relatives who were heterozygous for either of the mutations also had low levels of GP Ib alpha (74-90%). Hence, Bernard-Soulier patients homozygous or compound heterozygous for Tyr505(TAT) are severely affected. Interestingly, both mutations have independently been found in three other families in previous reports, suggesting their ancient age or mutational 'hot spot'.
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PMID:Molecular characterization of two mutations in platelet glycoprotein (GP) Ib alpha in two Finnish Bernard-Soulier syndrome families. 1008 93

Protein C (PC) is the zymogen of an anticoagulant serine protease and is converted to its active form (activated protein C: APC) by thrombin in the presence of thrombomodulin. APC plays an important role in regulating blood coagulation and fibrinolysis by inhibiting not only blood coagulation factors Va and VIIIa but also type-1 plasminogen activator inhibitor (PAI-1). In this study, it was reported that the antithrombotic effect of a human APC product (designated as CTC-111) compared with that of heparin and human PC on the deep venous thrombosis (DVT) model induced in mice by stasis caused by inferior vena cava ligation and operative invasion. Drugs were injected into a tail vein at -2, 30, 60, and 120 min after the inferior vena cava ligation. One-fifth amount of the total dosage of a given drug was injected at each time point. The wet weight of thrombus formed was reduced by APC or heparin administration, however, PC, which was equal to APC in protein amount, did not show any antithrombotic effect. To confirm whether human PC could be activated by mouse thrombin, PC was treated with mouse or human thrombin to measure the amount of APC formed. Mouse thrombin could activate human PC at a similar activation rate as human thrombin. These results suggest that externally administrated PC cannot exhibit antithrombotic effect in this DVT model due to slow activation rate to APC and that APC is a better antithrombic agent than PC for treating thrombotic diseases.
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PMID:Effect of activated human protein C on experimental venous thrombosis induced by stasis with operative invasion in mice. 1099 52

Protein C is the zymogen of an anticoagulant serine protease and is converted to its active form (activated protein C: APC) by thrombin in the presence of thrombomodulin. APC plays an important role in regulating coagulation and fibrinolysis by inactivating not only blood coagulation factors Va and VIIIa but also type-1 plasminogen activator inhibitor (PAI-1). The aim of the present study was to examine the effect of a human APC product (designated as CTC-111), compared with that of heparin, on the disseminated intravascular coagulation (DIC) induced by lipopolysaccharide (LPS) in rats. LPS (1 mg/kg/h) infusion was performed through a femoral vein for 4 h. One-fifth amount of the total dosage of CTC-111 or heparin was injected into the other femoral vein, followed by a 4-h infusion of the remainder. Both CTC-111 (10,000-100,000 U/kg) and heparin (400-800 IU/kg) inhibited the decrease in platelet count and fibrinogen level equally. The prolonged activated partial thromboplastin time and prothrombin time observed in DIC rats were further elongated in both CTC-111- and heparin-treated rats. But, this prolongation was less in CTC-111-treated rats than in the heparin-treated ones. Heparin inhibited the increase in fibrin and fibrinogen degradation products more prominently than CTC-111. On the other hand, CTC-111 strongly inhibited the increase in PAI-1 activity but heparin did not. These results suggest that CTC-111 may enhance fibrinolysis through its direct inhibitory effect on PAI-1. The parameters for liver or renal damage, i.e., plasma glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), creatinine (Cre) and blood urea nitrogen (BUN), were significantly increased by LPS infusion. Both CTC-111 (100,000 U/kg) and heparin (800 IU/kg) decreased the increase in GOT and GPT levels significantly, whereas neither affected the increase in Cre or BUN. From these results, the activation of the blood coagulation system might partially contribute to the progression of liver damage caused by LPS, and might be less involved in the progression of renal damage in this model. In conclusion, CTC-111 showed both anticoagulant and profibrinolytic activity in the LPS-induced DIC model without excessive prolongation of coagulation time. From these results, CTC-111 is expected to be a useful remedy for DIC without the risk of bleeding.
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PMID:Effect of activated human protein C on disseminated intravascular coagulation induced by lipopolysaccharide in rats. 1105 Jun 97