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

The possibility that platelet activation may also involve membrane (Na-K)ATPase was investigated by testing the effects of both proteinases on platelet shape change and aggregation in the absence and presence of the specific (Na-K)ATPase inhibitor ouabain. Ouabain (8 to 80 microM) completely antagonized trypsin-induced platelet shape change and aggregation when it was preincubated with platelet suspension before the addition of trypsin. Unlike trypsin, thrombin-induced platelet activation was significantly enhanced by ouabain. It was also observed that on partially purified beef heart (Na-K)ATPase preparation, thrombin significantly enhanced the enzyme inhibition caused by submaximal inhibitory concentrations of ouabain. Soybean trypsin inhibitor (4 micrograms/ml) employed as the agent capable to counteract proteinase effects on the (Na-K)ATPase, was shown both to prevent and antagonize the platelet activation induced by trypsin (0.3 to 1.5 micrograms/ml), but it failed to modify the responses evoked by thrombin. It is concluded that membrane (Na-K)ATPase is involved differently in platelet activation by trypsin and thrombin probably because receptor sites to which either proteinase on the platelet surface binds, are distinct. Direct enzyme involvement is indeed apparent only in trypsin-induced platelet activation.
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PMID:Differential involvement of membrane (Na-K)ATPase in thrombin- and trypsin-mediated platelet activation. 132 84

Ouabain, a digitalis glycoside and an inhibitor of the Mg2+-dependent Na+-K+ ATPase, was used to probe the role of intracellular Na+ levels in the regulation of platelet reactivity. Platelets preincubated with 10 to 150 microM ouabain exhibited a potentiated aggregation response to collagen (14.4 to 180 micrograms/mL), ADP (4 to 12 microM) and thrombin (0.03 to 0.10 unit/mL). Ouabain markedly decreased the time interval between addition of collagen and the onset of shape change. At submaximal concentrations of collagen, thrombin and ADP, preincubation with ouabain increased the rate and amplitude of the aggregation response. Irreversible aggregation was achieved in ouabain-treated platelets by using concentrations of ADP which induced only reversible aggregation in the absence of ouabain. In addition, chelation of extracellular calcium with EGTA or EDTA (2 mM) failed to block reactivity to collagen, ADP or thrombin in ouabain-treated platelets. These results suggest that ouabain induces a "preactivation state" in platelets, perhaps via modulation of intracellular Na+ levels.
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PMID:Ouabain affects platelet reactivity as measured in vitro. 311 Oct 4

Experiments were designed to analyze the effects of ouabain on the actions of exogenous arachidonic acid on endothelial and vascular smooth muscle cells. Rings or strips were prepared from left circumflex canine coronary arteries and suspended for isometric tension recording in organ chambers filled with oxygenated modified Krebs-Ringer-bicarbonate solution. During contractions evoked by prostaglandin F2 alpha, arachidonic acid caused relaxations both in the presence and the absence of endothelium. However, removal of the endothelium reduced its inhibitory action. Indomethacin prevented the relaxations in rings without endothelium, but did not affect the response to high doses (10(-6) to 10(-5) M) of arachidonic acid in preparations with endothelium. The inhibitor of lipoxygenase, nordihydroguaiaretic acid, had no effect on the inhibitory responses to arachidonic acid in rings with or without endothelium. Ouabain abolished both the endothelium-dependent and the direct relaxations to arachidonic acid. Endothelium-dependent relaxations in response to oleic acid, elaidic acid, adenosine diphosphate and thrombin were not affected by ouabain. In the presence of indomethacin, coronary artery strips without endothelium were relaxed by arachidonic acid only when layered (intimal surface against intimal surface) with a longitudinal strip with endothelium. In layered preparations, treatment of the intact longitudinal strip with ouabain before layering prevented the relaxation, whereas pretreatment of the strip without endothelium had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ouabain inhibits endothelium-dependent relaxations to arachidonic acid in canine coronary arteries. 393 Jul

The precise mechanisms of Ca2+ handling in rat platelets are not fully understood. We sought to determine whether rat platelets possess a Na(+)-Ca2+ exchanger. First, we investigated the time course of the effect of ouabain (10(-4) M) on cytosolic sodium concentration ([Na+]i) and Ca2+ homeostasis in platelets from Wistar rats in comparison with those from humans. Ouabain increased platelet [Na+]i in both rat and human platelets. Whereas ouabain induced a time-dependent increase in basal and thrombin-stimulated (0.3 units/ml) cytosolic calcium concentration ([Ca2+]i) in human platelets, no change was found in rat platelets. Furthermore, 90-min pretreatment of rat platelets with ouabain did not affect the [Ca2+]i response to thrombin (0.1-1.0 units/ml) or a maximal dose of ionomycin (5 microM). Also the decline in [Ca2+]i after the peak response evoked by these agonists in the absence of extracellular Ca2+ was not changed by ouabain pretreatment. Similarly, replacement of extracellular Na+ had no influence on any of these determinations. Thus decreasing the plasma membrane Na+ gradient did not affect basal [Ca2+]i, thrombin-induced mobilization of Ca2+ from intracellular stores, internal Ca2+ discharge capacity, or Ca2+ extrusion from cytosol of rat platelets. In contrast to human platelets, a Na(+)-Ca2+ exchange mechanism does not appear to play a significant role in Ca2+ homeostasis of rat platelets.
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PMID:Lack of effect of ouabain on calcium homeostasis in rat platelets: comparative study with human platelets. 816 Aug 57