Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phosphoinositide hydrolysis was studied in primary cultures of rat cerebellar astrocytes prelabeled with [3H]myo-inositol. Among the agonists examined, the rank order of efficacies in causing phosphoinositide hydrolysis was bradykinin > endothelin-1 > ATP > norepinephrine. The bradykinin response was robust (24-fold increase) with EC50 value of 30 nM and saturating concentration of 1 microM. Preincubation of cells with pertussis toxin did not affect the activation of phosphoinositide turnover by bradykinin. Although short-term (within 90 min) treatment of cells with phorbol dibutyrate attenuated bradykinin-induced phosphoinositide breakdown, the inhibitory effect was lost after 3-6 h of phorbol dibutyrate treatment. Extended (24 h) preincubation resulted in a potentiation of bradykinin response. Homologous desensitization of bradykinin response was observed in cells prestimulated with bradykinin for up to 6 h. However, similar to the effect of phorbol dibutyrate, 24-h pretreatment with bradykinin selectively sensitized the response to bradykinin. Up-regulation of the bradykinin response was also observed in cells prestimulated with endothelin-1 or norepinephrine for 24 h, although these treatments resulted in only homologous desensitization to their own response. Our results suggest that cultured cerebellar astrocytes express bradykinin receptors coupled to phospholipase C and in these cells protein kinase C plays a more prominent role in the negative-feedback regulation of bradykinin-evoked phosphoinositide response.
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PMID:Regulation of bradykinin-induced phosphoinositide turnover in cultured cerebellar astrocytes: possible role of protein kinase C. 133 44

The mitogenic effect of extracellular ATP on porcine aortic smooth muscle cells (SMC) was examined. Stimulation of [3H]thymidine incorporation by ATP was dose-dependent; the maximal effect was obtained at 100 microM. ATP acted synergistically with insulin, IGF-1, EGF, PDGF, and various other mitogens. Incorporation of [3H]thymidine was correlated with the fraction of [3H]thymidine-labeled nuclei and changes in cell counts. The stimulation of proliferation was also determined by measurement of cellular DNA using bisbenzamide and by following the increase of mitochondrial dehydrogenase protein. The effect of ATP was not due to hydrolysis to adenosine, which shows synergism with ATP. ATP acted as a competence factor. The mitogenic effect of ATP, but not adenosine, was further increased by lysophosphatidate, phosphatidic acid, or norepinephrine. The inhibitor of adenosine deaminase, EHNA, stimulated the effect of adenosine but not ATP. The adenosine receptor antagonist theophylline depressed adenosine-induced mitogenesis. ADP and the non-hydrolyzable analogue adenosine 5'-[beta, gamma-imido]triphosphate (AMP-PNP) were equally mitogenic. Thus extracellular ATP stimulated mitogenesis of SMC via P2Y purinoceptors. The mechanism of ATP acting as a mitogen in SMC was further explored. Extracellular ATP stimulated the release of [3H]arachidonic acid (AA) and prostaglandin E2 (PGE2) into the medium, and enhanced cAMP accumulation in a dose-dependent fashion similar to ATP-induced [3H]thymidine incorporation. Inhibitors of the arachidonic acid metabolism pathway, quinacrine and indomethacin, partially inhibited the mitogenic effect of ATP but not of adenosine. Pertussis toxin inhibited ATP-stimulated DNA synthesis, AA release, PGE2 formation, and cAMP accumulation. Down-regulation of protein kinase C (PKC) by long-term exposure to phorbol dibutyrate (PDBu) partially prevented stimulation of DNA synthesis and activation of the AA pathway by ATP. The PKC inhibitor, staurosporine, antagonized mitogenesis stimulated by ATP. No synergistic effect was found when PDBu and ATP were added together. Therefore, a dual mechanism, including both arachidonic acid metabolism and PKC, is involved in ATP-mediated mitogenesis in SMC. In addition, ATP acted synergistically with angiotensin II, phospholipase C, serotonin, or carbachol to stimulate DNA synthesis. Finally, the possible physiological significance of ATP as a mitogen in SMC was further studied. The effect of endothelin and heparin, which are released from endothelial cells, on ATP-dependent mitogenesis was investigated. Extracellular ATP acted synergistically with endothelin to stimulate a greater extent of [3H]thymidine incorporation than was seen with PDGF plus endothelin. Heparin, believed to have a regulatory role, partially inhibited the stimulation of DNA synthesis caused both by ATP and PDGF.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Extracellular ATP and ADP stimulate proliferation of porcine aortic smooth muscle cells. 135 98

The role of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) in mediating various Ca2+ signaling pathways was examined in PC12 cells. Conversion of the kinase to a Ca(2+)-independent form was used to monitor which neurotransmitters activate the enzyme in situ. CaM kinase responds to Ca2+ influx elicited by ligand-gated Ca2+ channels for ATP and acetylcholine. It also responds to Ca2+ mobilization of IP3-sensitive stores elicited by phospholipase C-linked receptors for ATP and acetylcholine as well as by caffeine. CaM kinase mediates the actions of many neurotransmitters and Ca2+ signaling pathways.
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PMID:Multiple Ca2+ signaling pathways converge on CaM kinase in PC12 cells. 137 43

Cultured aortic fibroblasts express high affinity Et-1 binding sites that poorly discriminate between Et-1 and Et-3. Both endothelins activate phospholipase C hence indicating the presence of ETB receptors. Fibroblasts respond to bradykinin by large activations of phospholipase C and increases in [Ca2+]i in a manner that was abolished by D-Arg, [Hyp3,Thi5,8,D-Phe7]-bradykinin, thus indicating the presence of B2 kinin receptors. Finally, ATP, UTP and ADP increases [Ca2+]i in aortic fibroblasts via a nucleotide receptor that has a higher affinity for ATP and UTP (3 microM) than for ADP (50 microM) and that is distinct from P2x and P2y purinoceptors.
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PMID:High reactivity of aortic fibroblasts to vasoactive agents: endothelins, bradykinin and nucleotides. 141 43

Rhodopsin kinase activity of Musca domestica was characterized in a reconstitution assay, using urea-treated eye membranes as substrate and a purified fraction of eye cytosol as the enzyme. Analysis of kinase activity in fly eye, brain and abdomen extracts by reconstitution assays revealed that fly rhodopsin kinase is an eye-specific enzyme. It preferentially phosphorylates the light-activated form of rhodopsin (metarhodopsin) and has little activity with other protein substrates. Rhodopsin kinase binds to metarhodopsin and is released from rhodopsin-containing membranes. Metarhodopsin is a poor substrate for kinases from tissues other than the eye, making it a unique substrate for rhodopsin kinase. Rhodopsin kinase is inhibited by heparin, but not by the protein inhibitor of cAMP-dependent protein kinase. Its Km for ATP is 9 microM. Since fly rhodopsin is coupled to phospholipase C, studies of the interaction of rhodopsin with rhodopsin kinase can be useful in analysis of the reactions that lead to termination of the inositol-phospholipid-signaling pathway.
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PMID:Characterization of fly rhodopsin kinase. 142 85

Staphylococcus aureus alpha-toxin is a pore-forming exotoxin that probably represents a significant virulence factor in staphylococcal infections. Previous studies demonstrated that this agent stimulated arachidonate metabolism with subsequent formation of prostacyclin in endothelial cells and leukotriene B4 in granulocytes. We now examined the effect of alpha-toxin on the synthesis of platelet-activating factor (PAF) in cultured porcine pulmonary artery endothelial cells. PAF was labeled by bioincorporation of tritiated acetate and separated/quantitated using thin-layer chromatography, straight-phase-HPLC, or post-HPLC-bioassay. Alpha-toxin induced synthesis of small amounts of PAF in a time- and dose-dependent manner. The maximal amount of PAF elicited by alpha-toxin was approximately 7% of that observed after application of the ionophore A23187. Staphylococcal alpha-toxin but not the ionophore induced a rapid fall in cellular ATP-content. On kinetic grounds, the decrease in ATP-levels did not explain the differences in stimulated PAF-synthesis. Low amounts of PAF induced by the action of alpha-toxin on endothelial cells may contribute to the development of inflammatory lesions in infectious disease.
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PMID:Stimulation of PAF-synthesis in pulmonary artery endothelial cells by Staphylococcus aureus alpha-toxin. 144 May 26

Myocardial cell vulnerability to phospholipase C (PC-PLC) attack was investigated in three different preparations of rat myocardial cells: triacylglycerol (TG)-loaded, hypothermic/rewarmed and energy depleted myocytes. The attack by PC-PLC was evaluated as PC-PLC induced glycerol output due to the combined action of phospholipase C and intracellular lipases. PC-PLC induced glycerol output was significantly higher (p < 0.05) in all three myocyte preparations, compared to their respective controls. Cell morphology (% rod shaped myocytes) of TG-loaded or hypothermic/rewarmed myocytes was not different from their controls, whereas energy depleted myocytes almost exclusively were rounded up, due to hypercontraction of the myofilaments. Hypothermic/rewarmed and energy depleted myocytes showed a significantly higher release of lactate dehydrogenase (LDH), compared to their controls although the difference was much more pronounced in the latter. Finally, the cellular contents of ATP were maintained both in TG-loaded and hypothermic rewarmed myocytes, while energy depleted myocytes contained only about 25% of the normal ATP level. These results demonstrate that attack from exogenously added phospholipases can occur, not only in seriously damaged cardiac myocytes, but in myocytes with a more subtle damage as well.
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PMID:Myocardial cell vulnerability to exogenous phospholipase attack. 148 Jan 54

There is evidence suggesting that fluid shear stress activates phospholipid turnover in endothelial cells, but it is not clear which phospholipids are involved in the transduction of the flow signal. Cultured human umbilical-vein endothelial cells were prelabeled with [14C]-arachidonic acid and subjected to laminar shear stresses of 0.4, 1.4 and 22 dyn/cm2 for times up to 30 min, after which the distribution of the radioactivity in the phospholipids was determined. We observed decreases in labeled phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid at 10-30 s, and increases in labeled diacylglycerol (DG) and free arachidonate, as well as a simultaneous elevation in inositol 1,4,5-triphosphate (IP3) levels. A second peak in IP3 levels was observed 10 min after the onset of shear. This is in contrast with agonist-stimulated endothelial cells, where IP3 levels go back to initial values within a few minutes after stimulation. The flow-induced IP3 response was the same in the presence or absence of ATP and serum in the perfusing medium. These results are consistent with the activation of phospholipase C, phospholipase A2 and DG lipase by shear stress. This suggests that several phospholipids are involved in the production of free arachidonic acid and DG, which are likely to be important mediators of the shear stress signal. In addition, flow may lead to a chronic stimulation of endothelial-cell metabolism.
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PMID:Fluid shear stress stimulates membrane phospholipid metabolism in cultured human endothelial cells. 148 90

The Ca2+ ion exerts a profound influence on cellular processes and an understanding of control mechanisms of intracellular Ca2 homeostasis while complex is mandatory in this discussion. The identification and recognition of prolonged sustained increase in [Ca2+]i as a manifestation of neurotoxin-induced destabilization of [Ca2+]i homeostasis will be related to a variety of neurotoxicant-induced cell injuries. The sites of toxicant interaction with ATP-regulated Ca2+ pumps located in the neuronal/glial membrane and/or calciosomes; availability of Ca2+ proteins; disruption in mitochondrial mechanisms for Ca2+ storage; triggers of voltage-dependent Ca2+ channels and modulation of the Na+/Ca2+ exchanger will be identified and related to presumptive toxin action. Failure of one or more of these systems will result in continuous elevation of ionized [Ca2+]i--a reflection of Ca2+ destabilization. The targets resulting from Ca2+ destabilization will be identified, to include phospholipase C activation, PLA2 activation, protein kinase C (PKC) translocation, and activation of Ca(2+)-dependent calpain 1. The use of specific inhibitors of neurotoxicity, e.g., natural sphingolipids, sphingosine, down regulation of PKC, inhibitors and activators of adenylate cyclase, and antiprotease agents will allow for investigation of the role of these final common pathways in the evolution of neurotoxicity.
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PMID:Ca(2+)-dependent processes as mediators of neurotoxicity. 150 13

Soluble and membrane-bound low-Km 5'-nucleotidase was isolated from high-speed supernatants and membrane fractions derived from the electric organ of the electric ray (Torpedo marmorata) or from bovine brain cerebral cortex. Purification of both enzymes included chromatography on concanavalin A-Sepharose and AMP-Sepharose. The contribution to the total of soluble enzyme activity was lower in electric organ (1.6%) than in bovine cerebral cortex (27.9%). Membrane-bound and soluble forms have very similar Km values for AMP and are inhibited by micromolar concentrations of ATP. Both forms cross-react with, and are inhibited by, an antibody against the membrane-bound surface-located (ecto-) 5'-nucleotidase from electric organ. The HNK-1 carbohydrate epitope is present on both forms of the Torpedo enzyme, but is entirely absent from bovine cerebral-cortex 5'-nucleotidase. An antibody specific for the inositol 1,2-(cyclic)monophosphate that is formed on phospholipase C cleavage of an intact glycosyl-phosphatidylinositol (GPI) anchor binds to the soluble, but not to the membrane-bound, form of the enzyme from both sources. Our results suggest that soluble low-Km 5'-nucleotidase in both electric organ and bovine brain is derived from the membrane-bound GPI-anchored form of the enzyme by the action of a phospholipase C and is not a soluble cytoplasmic enzyme.
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PMID:Soluble low-Km 5'-nucleotidase from electric-ray (Torpedo marmorata) electric organ and bovine cerebral cortex is derived from the glycosyl-phosphatidylinositol-anchored ectoenzyme by phospholipase C cleavage. 153 75


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