Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.86 (clotting enzyme)
 176 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The action of the blood clotting enzyme thrombin on single channel and whole cell Ca(2+)-currents was studied in isolated mammalian cardiac myocytes. Thrombin, at a concentration of 10(-8) mol/l, increased the Ca(2+)-channel activity in cell-attached patches. The mean open probability of the channel was enhanced, while the number of sweeps without openings, which reflects the availability of the channel, was significantly reduced. Neither the single channel conductance nor the activation curve were affected by thrombin. Thrombin was added to the bath solution, and its effect is therefore indirect and probably mediated via a second messenger. However, thrombin did not affect whole-cell Ca(2+)-currents, whereas a beta-adrenergic stimulation in the same cell increased the Ca(2+)-current. It is concluded that thrombin affects an intracellular mechanism for Ca2+ channel current regulation, which is still unknown and which is rapidly lost during conventional whole-cell Ca2+ current measurements.
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PMID:Thrombin stimulates L-type calcium channels of guinea pig cardiomyocytes in cell-attached patches but not after intracellular dialysis. 131 2

The clotting enzyme thrombin induces not only blood coagulation but it also receptor-mediated cellular events. In our studies, thrombin at nanomolar concentrations caused irreversible aggregation of washed human platelets which was inhibited by the naturally occurring tight-binding inhibitor hirudin. Thrombin within the same concentration range caused concentration-dependent transient relaxation of PGF2 alpha-precontracted pig coronary artery ring segments with intact endothelium. The relaxant response was neither affected by indomethacin nor by verapamil and was only slightly inhibited by exposure to calcium-free medium. Methylene blue enhanced the PGF2 alpha-induced contraction and diminished the thrombin-induced relaxation. Hirudin inhibited the relaxant effect of thrombin in a concentration-dependent manner. After removal of the endothelium by mechanical rubbing the thrombin-induced relaxation was absent. The present studies suggest that thrombin generated during coagulation is able to modify the vascular smooth muscle tone.
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PMID:Studies on thrombin-induced endothelium-dependent vascular effects. 320 49

Adrenomedullin recently has been found to potently stimulate cAMP formation in cultured rat vascular smooth muscle cells (VSMCs). In the present study, we examined the effect of adrenomedullin on the production of a vasoconstrictive and growth-promoting peptide, endothelin-1, after stimulation with a clotting enzyme, thrombin, and a potent mitogen, platelet-derived growth factor (PDGF), in cultured rat VSMCs. Thrombin and PDGF stimulated endothelin-1 production in a dose-dependent manner. Rat adrenomedullin significantly inhibited thrombin- and PDGF-stimulated endothelin-1 production in a dose-dependent manner between 10(-7) and 10(-9) mol/L. Inhibition by rat adrenomedullin of thrombin- and PDGF-stimulated endothelin-1 production was paralleled by an increase in the cellular level of cAMP. Human adrenomedullin also inhibited thrombin- and PDGF-stimulated endothelin-1 production and increased cAMP levels. The addition of 8-bromo-cAMP, a cAMP analogue, reduced thrombin- and PDGF-induced endothelin-1 production. Furthermore, forskolin, a potent activator of adenylate cyclase, reduced thrombin- and PDGF-induced endothelin-1 production. In contrast, basal production of endothelin-1 was not altered by rat or human adrenomedullin. These results indicate that adrenomedullin inhibits not basal but thrombin- and PDGF-induced ET-1 production in cultured VSMCs probably through a cAMP-dependent process. Taken together with the finding that adrenomedullin is synthesized in and secreted from vascular endothelial cells, adrenomedullin may modulate vascular tone as a paracrine regulator partially through the inhibition of VSMC endothelin-1 production in some pathophysiological states.
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PMID:Inhibition of endothelin production by adrenomedullin in vascular smooth muscle cells. 776 61

Endothelium is a multifunctional organ which can directly influence circulating blood components as well as other cells within the vessel wall. The clotting enzyme thrombin, generated at the surface of damaged endothelium, induces blood coagulation but also exerts a variety of functional effects on the endothelium itself. Thrombin acts on endothelial cells to stimulate synthesis and release of various agents, such as inflammatory mediators, vasoactive substances and growth factors. It causes leukocyte adhesion to the endothelium by triggering expression of adhesion molecules on the cell surface and causes disruption of endothelial permeability properties. The majority of thrombin effects on endothelial cells are mediated by its receptor and require its lytic activity. Differences have been observed among the response to thrombin of endothelial cells of different origin. In general microvascular endothelial cells appear to be particularly sensitive to this enzyme. Thrombin induced microvascular dysfunction can have pathological consequences and contribute to organ reactions to inflammation and ischaemia.
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PMID:Thrombin-induced endothelial cell dysfunction. 780 40

Thrombin, the blood-clotting enzyme, is a serine proteinase with trypsin-like specificity and is able to cleave Arg-Xaa peptide bonds but only in a very limited number of substrates (and sites therein). For the prevention and treatment of thrombosis the control of thrombin activity is a key target, and a variety of synthetic inhibitors have been introduced recently, all of which have a positive charge at the P1 site. We report the synthesis of the first example of a new class of inhibitor containing a neutral side chain at the P1 site, the peptide benzyloxycarbonyl-D-Phe-Pro- methoxypropylboroglycine. The peptide is a potent inhibitor of thrombin [Ki (limiting) = 7 nM] and is highly selective for its target enzyme in respect of other serine proteinases. This may be expected to confer considerable advantage in terms of specificity of action and reduced toxicity over conventional, positively charged, inhibitors.
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PMID:Benzyloxycarbonyl-D-Phe-Pro-methoxypropylboroglycine: a novel inhibitor of thrombin with high selectivity containing a neutral side chain at the P1 position. 845 16

Thrombin is a key blood clotting enzyme; therefore, developing of its inhibitors has become a mainstream in antithrombotic pharmacology. As a result, a wide variety of proteins, peptides, peptidomimetics, DNA, RNA, and carbohydrates were reported to be effective inhibitors of thrombin activities. The majority of described inhibitors were characterized kinetically with amidolytic assay only; though some of them inhibit fibrinogen binding rather than amidolytic activity, e.g. hirugen and nucleic acid aptamers. Per contra, studying the inhibition kinetics of fibrinogen hydrolysis might reveal essential peculiarities of mechanism of action of thrombin inhibitors. In this paper the effect of thrombin inhibitors on fibrinogen hydrolysis has been investigated using improved turbidimetric assay. This technique is highly productive versus fibrinopeptide determination allowing elucidation of inhibition type and apparent constant for different types of thrombin inhibitors. The protein (recombinant hirudin, antithrombin III), peptide (bivalirudin, hirugen), and peptidomimetic (argatroban, PPACK) inhibitors were characterized in terms of inhibition types for the first time. Unexpectedly, for others: heparin, RNA aptamer Toggle-25t, partial inhibition has been shown indicating allosteric interplay between exosites. Improved turbidimetric assay is also applicable for studying the fibrin association inhibitors. Hence, GPRP-peptide was characterized kinetically for the first time. The kinetic study revealed a repertoire of different inhibition types and also close allosteric interplay within the thrombin. The results are undoubtedly important for understanding the enzyme activity regulation, as well as for the rational development of new antithrombotic substances.
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PMID:Multiple inhibitory kinetics reveal an allosteric interplay among thrombin functional sites. 2546 79