Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

DDT1-MF2 smooth muscle cells demonstrated a robust phospholipase C response to norepinephrine, as detected by inositol phosphate accumulation. A selective A1-adenosine receptor agonist, cyclopentyladenosine, caused only a minor stimulation of phospholipase C, which was eliminated in the absence of added extracellular calcium. The simultaneous addition of norepinephrine and cyclopentyladenosine resulted in a synergistic increase in phosphoinositide hydrolysis either in the absence or in the presence of external calcium. In the presence of external calcium and a calcium ionophore, and adenosine agonist caused a significant stimulation of phosphoinositide hydrolysis without the addition of norepinephrine. Influx of extracellular calcium through voltage-sensitive calcium channels did not appear to be required to observe an effect of cyclopentyladenosine, because neither calcium channel antagonists (nifedipine, verapamil, and LaCl3) nor a chelator of extracellular calcium (ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid) were able to alter the degree of potentiation of norepinephrine-stimulated phosphoinositide hydrolysis due to the adenosine agonist. On the other hand, buffering of intracellular calcium concentration with the membrane-permeant calcium chelator quin2 blocked the potentiation. This blockade of potentiation by quin2 was reversed by the addition of extracellular calcium. Agents that stimulated cAMP production or membrane-permeable analogues of cAMP also blocked the action of the adenosine agonist to potentiate norepinephrine-stimulated phosphoinositide hydrolysis. This effect of cAMP was less pronounced in the presence of elevated extracellular calcium and was abolished in the presence of a calcium ionophore. When norepinephrine-stimulated calcium transients were quantitated using fura-2 fluorescence, a reduction in the amplitude of the calcium response was observed in the presence of forskolin. Conversely, both the amplitude and the duration of the calcium response were enhanced by the addition of the adenosine agonist. The results of these studies suggest that the mechanism by which adenosine receptors enhance the stimulation of phosphoinositide hydrolysis is dependent upon a rise in intracellular Ca2+ concentration resulting from the simultaneous activation of alpha 1-adrenergic receptors. The results further suggest that cAMP inhibits this mechanism by decreasing the norepinephrine-stimulated rise in intracellular Ca2+ concentration.
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PMID:Competitive regulation of phospholipase C responses by cAMP and calcium. 131 17

The activation of adenosine A1 receptors in DDT1-MF2 smooth muscle cells resulted in both the inhibition of agonist-stimulated cAMP accumulation and the potentiation of norepinephrine-stimulated phosphoinositide hydrolysis. Pharmacological analysis indicated the involvement of an A1 adenosine receptor subtype in both of these responses. In the absence of norepinephrine, the activation of the adenosine receptor did not directly stimulate phosphoinositide hydrolysis. The adenosine receptor-mediated augmentation of norepinephrine-stimulated phosphoinositide hydrolysis was pertussis toxin sensitive and was selectively antagonized by agents that mimicked cAMP (8-bromo-cAMP) or raised cellular cAMP levels (forskolin). This initially suggested that cAMP might partially regulate the magnitude of the phospholipase C response to norepinephrine and that adenosine agonists might enhance the phospholipase C response by reducing cAMP levels. However, neither the reduction of cellular cAMP levels by other agents nor the inhibition of cAMP-dependent protein kinase was sufficient to replicate the action of adenosine receptor activation on phosphoinositide hydrolysis. Thus, in the presence of norepinephrine, adenosine receptor agonists appear to stimulate phosphoinositide hydrolysis via a pathway that is separate from, but dependent upon, that of norepinephrine. This second pathway can be distinguished from that which is stimulated by norepinephrine on the basis of its sensitivity to inhibition by both cAMP and pertussis toxin.
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PMID:Cyclic AMP differentiates two separate but interacting pathways of phosphoinositide hydrolysis in the DDT1-MF2 smooth muscle cell line. 131 18

1. The presence of adenosine receptors linked to adenylate cyclase activity and their functional role in calcium-evoked 5-hydroxytryptamine (5-HT) release was investigated in rat basophilic leukaemia (RBL) cells, a widely used model for studying the molecular mechanisms responsible for stimulus-secretion coupling. 2. In [3H]-5-HT-loaded cells triggered to release by the calcium ionophore A23187, a biphasic modulation of 5-HT secretion was induced by adenosine analogues, with inhibition of stimulated release at nM and potentiation at microM concentrations, suggesting the presence of adenosine receptor subtypes mediating opposite effects on calcium-dependent release. This was also confirmed by results obtained with other agents interfering with adenosine pharmacology, such as adenosine deaminase and the non-selective A1/A2 antagonist 8-phenyl-theophylline. 3. Similar biphasic dose-response curves were obtained with a variety of adenosine analogues on basal adenylate cyclase activity in RBL cells, with inhibition and stimulation of adenosine 3':5'-cyclic monophosphate (cyclic AMP) production at nM and microM concentrations, respectively. The rank order of potency of adenosine analogues for inhibition and stimulation of adenylate cyclase activity and the involvement of G-proteins in modulation of cyclic AMP levels suggested the presence of cyclase-linked A1 high-affinity and A2-like low-affinity adenosine receptor subtypes. However, the atypical antagonism profile displayed by adenosine receptor xanthine antagonists on cyclase stimulation suggested that the A2-like receptor expressed by RBL cells might represent a novel cyclase-coupled A2 receptor subtype.4. Micromolar concentrations of adenosine analogues could also increase inositol phospholipid hydrolysis and inositol tris-phosphate formation in both unstimulated cells and in cells triggered to release by the calcium ionophore. The stimulation was constant, small and additive to that exerted by the calcium ionophore.5. It is concluded that RBL cells express both A1 and A2-like adenosine receptors which exert opposite effects on 5-HT release and intracellular cyclic AMP levels. However, besides modulation of cyclic AMP levels, additional transduction pathways, such as modulation of phospholipase C activity, may contribute to the release response evoked by adenosine analogues in this cell-line.
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PMID:Adenosine receptors in rat basophilic leukaemia cells: transductional mechanisms and effects on 5-hydroxytryptamine release. 131 28

We have previously reported that in several renal cell types, adenosine receptor agonists inhibit adenylyl cyclase and activate phospholipase C via a pertussis toxin-sensitive G protein. In the present study, in 28A cells, both of these adenosine receptor-mediated responses were inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a highly selective A1 adenosine receptor antagonist. The binding characteristics of the adenosine A1 receptor in the 28A renal cell line were studied using the radiolabeled antagonist [3H]DPCPX to determine whether two separate binding sites could account for these responses. Saturation binding of [3H]DPCPX to 28A cell membranes revealed a single class of A1 binding sites with an apparent Kd value of 1.4 nM and maximal binding capacity of 64 fmol/mg protein. Competition experiments with a variety of adenosine agonists gave biphasic displacement curves with a pharmacological profile characteristic of A1 receptors. Comparison of [3H]DPCPX competition binding data from 28A cell membranes with rabbit brain membranes, a tissue with well-characterized A1 receptors, reveals that the A1 receptor population in 28A cells has similar agonist binding affinities to the receptor population in brain but has a considerably lower density. Addition of guanosine 5'-triphosphate (100 microM) to 28A cell membranes caused the competition curves to shift from biphasic to monophasic, indicating that the A1 receptors exist in two interconvertible affinity states because of their coupling to G proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of adenosine A1 receptor in a cell line (28A) derived from rabbit collecting tubule. 132 20

To determine which subtype of adenosine receptor mediates the potentiating effect of 2-chloroadenosine on the noradrenaline-induced inositol-phosphate formation, we used the monoclonal anti-idiotypic antibody AA1 that acts as an 'internal image' of adenosine and specifically recognizes the A1 adenosine receptor. In cultured mouse striatal astrocytes, AA1 increased the noradrenaline-evoked inositol phosphate (IP) accumulation, thus demonstrating a biological activity of an anti-idiotypic antibody. This effect was inhibited by PACPX, a selective A1 antagonist. Inhibitors of phospholipase A2 activity prevented the potentiation. These results establish the involvement of A1 adenosine receptors in the modulation of phospholipase C activity.
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PMID:A monoclonal anti-idiotypic 'internal image' antibody that recognizes the A1 adenosine receptor potentiates the alpha 1-adrenergic activation of phospholipase C in primary cultures of mouse striatal astrocytes. 133 41

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

Phospholipid metabolism is altered during ischemia and post-ischemic reperfusion. Past studies demonstrating elevated myocardial free fatty acid and lysophospholipid content infer accelerated phospholipid degradation involving phospholipase A activity. Recently, ischemic and post-ischemic reperfusion (reperfusion) have been shown to affect levels of phosphoinositide (PPI) degradation products. Considering the role of PPI turnover in regulation of cellular calcium homeostasis, our laboratory and others have suggested that alteration in the metabolism of the inositol phospholipids could play a role in the development of ischemia-induced calcium overload injury. Using an isolated rat heart model (Langendorff perfusion), this study examines the effect of global ischemia and reperfusion on ventricular phosphoinositide-specific phospholipase C (PLC) activity and PLA2 activity. The primary purpose was to determine if ischemia and reperfusion-induced changes in PLC activity could explain previously observed changes in PPI degradation products, and whether PLC and PLA2 activities were similarly or differentially altered by ischemia and reperfusion. PLC and PLA2 activities were measured in cytosolic and total membrane fractions from control (perfused), ischemic (5, 10, 30, and 60 min), and post-ischemic reperfused ventricular tissue. Phospholipase activity was determined under optimal in vitro conditions using exogenous radiolabeled substrates. Alterations in membrane-associated PPI-PLC activity correlated with reported ischemia and reperfusion-induced changes in ventricular content of PPI metabolites. Membrane PLC activity increased slightly at 5 min of ischemia, decreased significantly at 10 min of ischemia, and continued to decrease with longer duration of ischemia (73% of control after 60 min). Cytosolic PPI-PLC activity was decreased at 5 min, and then significantly increased by longer durations of ischemia, while cytosolic PLA2 activity was reduced at all time points. Pretreatment with muscarinic, alpha 1-adrenergic, beta-adrenergic, and adenosine receptor blockers did not alter ischemia-elicited changes in PLC activity. Reperfusion caused a 140% to 200% rise in the activities of all phospholipases in all fractions after 40 min of ischemia, but not after 10 min of ischemia. Results suggest 1) ischemia and reperfusion-elicited alterations in membrane-associated PPI-PLC activity can explain previously observed changes in phosphoinositide turnover metabolites, 2) cytosolic and membrane-associated PPI-PLC and PLA2 activities are not uniformly affected by ischemia, 3) reperfusion following ischemia of sufficient duration initiates uniform activation of PIP2-PLC and PLA2, and 4) because ischemia and reperfusion-induced changes in phospholipase activity can be detected under optimal in vitro assay conditions (removed from the in vivo ischemic microenvironment), it is likely that the enzymes themselves have been altered.
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PMID:Changes in phosphoinositide-specific phospholipase C and phospholipase A2 activity in ischemic and reperfused rat heart. 159 Jul 34

The effect of adenosine on phosphoinositide hydrolysis was examined in 1321N1 human astrocytoma cells. Adenosine, L-N6-phenylisopropyladenosine (L-PIA), and 5'-(N-ethylcarboxamido)adenosine (NECA) inhibited histamine-stimulated accumulation of inositol phosphates in a concentration-dependent manner. The potency order of adenosine analogues for inhibition of inositol phosphate accumulation was L-PIA greater than adenosine greater than NECA, a finding indicating that A1-class adenosine receptors are involved in the inhibition. The reduction in inositol phosphate accumulation by L-PIA was blocked by an adenosine receptor antagonist, 8-phenyltheophylline. Stimulation of A1-class adenosine receptors inhibited isoproterenol-stimulated cyclic AMP accumulation as well as histamine-induced inositol phosphate accumulation. Both inhibitory effects were blocked by pretreatment of the cells with pertussis toxin [islet-activating protein (IAP)]. L-PIA also inhibited guanosine 5'-(gamma-thio)triphosphate (GTP gamma S)-stimulated accumulation of inositol phosphates in membrane preparations, and 8-phenyl-theophylline antagonized the inhibition. L-PIA could not inhibit GTP gamma S-induced accumulation of inositol phosphates in IAP-treated membranes. Gi/Go, purified from rabbit brain, inhibited GTP gamma S-stimulated accumulation of inositol phosphates in a concentration-dependent manner in membrane preparations. These results suggest that stimulation of A1-class adenosine receptors interacts with the IAP-sensitive G protein(s), resulting in the inhibitions of phospholipase C as well as adenylate cyclase in human astrocytoma cells.
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PMID:Adenosine inhibits histamine-induced phosphoinositide hydrolysis mediated via pertussis toxin-sensitive G protein in human astrocytoma cells. 165 Mar 98

The effect of adenosine, 2-chloroadenosine (CAD), and 5'-(N-ethylcarboxamido)-adenosine (NECA) on the contraction produced by phorbol 12,13-dibutyrate (PDB) was investigated in porcine coronary artery in vitro to determine whether adenosine receptor-mediated relaxation was linked to protein kinase C. Also, the coronary relaxation produced by adenosine and NECA in KCl-contracted coronary rings was investigated before and after treatment with the phospholipase C inhibitor neomycin to examine a possible link between phospholipase C and adenosine receptor-mediated relaxation. Ring segments of coronary artery were suspended in organ baths for measurement of isometric force. PDB (10 nM-1 microM) caused concentration-dependent contraction, and this response was significantly attenuated by pretreatment with the protein kinase C inhibitor staurosporine (200 nM) but not 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (10 microM). Treatment of rings with either adenosine, CAD, or NECA (100 microM) significantly attenuated the PDB-induced contraction, whereas treatment with either sodium nitroprusside (SNP; 1 microM) or isoproterenol (Isop; 1 microM) did not affect the contraction produced by PDB. The attenuation of the PDB-induced contraction by adenosine and its analogues was blocked by prior treatment of the coronary rings with 8-phenyltheophylline (10 microM). In a separate series of experiments, pretreatment of rings with the phospholipase C inhibitor neomycin (1 mM) resulted in a significant attenuation of the relaxing response to both adenosine and NECA while having no significant effect on the relaxation-response to SNP or Isop. These results provide indirect evidence that adenosine receptor-mediated relaxation in porcine coronary artery may be linked to modulation of protein kinase C and phospholipase C.
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PMID:Protein kinase C and phospholipase C in adenosine receptor-mediated relaxation in coronary artery. 175 May 39

Norepinephrine (NE) stimulated FRTL-5 thyroid cells via an alpha 1-adrenergic receptor, resulting in cytosolic Ca2+ [( Ca2+]i) mobilization and activation of phospholipase C. Adenosine and its receptor agonist, phenylisopropyladenosine (PIA), although not exerting a direct effect, markedly enhanced the NE-induced changes. Basal NE action was not totally abolished whereas the permissive action of adenosine and PIA was completely abolished by pretreatment of the cells with islet-activating protein (IAP), pertussis toxin. The decrease in cAMP level induced by adenosine or PIA is not the cause of their permissive effect, since the effect was not reversed by the addition of cAMP-increasing agents. We conclude that an IAP substrate GTP-binding protein(s) plays a novel role in forming a stimulatory coupling between an adenosine receptor and an alpha 1-adrenergic receptor-coupled phospholipase C system.
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PMID:Stimulation of adenosine receptor enhances alpha 1-adrenergic receptor-mediated activation of phospholipase C and Ca2+ mobilization in a pertussis toxin-sensitive manner in FRTL-5 thyroid cells. 254 83


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