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)

Porcine or bovine endothelial cells cultured on microcarrier beads, packed into adapted chromatographic columns, perfused with Krebs' buffer and activated with appropriate stimuli (e.g. bradykinin, ADP or phospholipase C) release EDRF and prostacyclin into the perfusing fluid. In the effluent EDRF and prostacyclin might be bio-assayed using the Vane's superfusion cascade (rabbit aortic strips and bovine coronary artery strips, respectively) against nitroglycerine (GTN) and synthetic prostacyclin standards. Prostacyclin might be also quantified as 6-keto-PGF1 alpha by RIA. A spatial separation of the generator (endothelial cells) from the effector (vascular smooth muscle) has allowed to prove that EDRF is nitric oxide, that its activity is inhibited by superoxide anions and by chemicals which act via free radicals, finally, that the release of EDRF and prostacyclin is coupled by a receptor-mediated activation of phospholipase C. Although so successful, the above technique suffers from its essentials, i.e. from using cultured cells instead of fresh intact endothelial cells. Cultured endothelial cells are not responsive to many receptor agonists including acetylcholine, substance P and 5-hydroxytryptamine. Unlike fresh intact endothelial preparations the cultured cells which are perfused with Krebs' buffer generate superoxide anions at such concentrations that it might be obligatory infusing superoxide dismutase in order to detect EDRF. Nonetheless, a couple of data obtained with the cultured endothelial cells have been reproduced in the fresh cell preparations, e.g. release of EDRF by ADP and ATP, a coupled release of EDRF and prostacyclin by phospholipase C or a paradoxical augmentation of the sodium-nitroprusside-induced vasorelaxation by methylene blue.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Endothelium-derived relaxing factor (EDRF) from cultured and fresh endothelial cells. 247 Mar 61

We have investigated the effects of in vivo lithium treatment on cerebral inositol phospholipid metabolism. Twice-daily treatment of rats with LiCl (3 mEq/kg) for 3 or 16 days resulted in a 25-40% reduction in agonist-stimulated inositol phosphate production, compared with NaCl-treated controls, in cortical slices prelabelled with [3H]inositol. A small effect was also seen with 5-hydroxytryptamine (5-HT) 24 h after a single dose of LiCl (10 mEq/kg). Dose-response curves to carbachol and 5-HT showed that lithium treatment reduced the maximal agonist response without altering the EC50 value. This inhibition was not affected by the concentration of LiCl in the assay buffer. Stimulation of inositol phosphate formation by 10 mM NaF in membranes prepared from cortex of 3-day lithium-treated rats was also inhibited, by 35% compared with NaCl-treated controls. Lithium treatment did not alter the kinetic profile of inositol polyphosphate formation in cortical slices stimulated with carbachol. Muscarinic cholinergic and 5-HT2 bindings were unaltered by lithium, as was cortical phospholipase C activity and isoproterenol-stimulated cyclic AMP formation. [3H]Inositol labelling of phosphatidylinositol 4,5-bisphosphate was significantly enhanced by 3-day lithium treatment. The results, therefore, indicate that subacute or chronic in vivo lithium treatment reduces agonist-stimulated inositol phospholipid metabolism in cerebral cortex; this persistent inhibition appears to be at the level of G-protein-phospholipase C coupling.
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PMID:Subacute and chronic in vivo lithium treatment inhibits agonist- and sodium fluoride-stimulated inositol phosphate production in rat cortex. 253 74

The signal transduction pathways of the cloned human 5-HT1A receptor have been examined in two mammalian cell lines transiently (COS-7) or permanently (HeLa) expressing this receptor gene. In both systems, 5-hydroxytryptamine (5-HT, serotonin) mediated a marked inhibition of beta 2-adrenergic agonist-stimulated (80% inhibition in COS-7 cells) or forskolin-stimulated cAMP formation (up to 90% inhibition in HeLa cells). This serotonin effect (EC50 = 20 nM) could be competitively antagonized by metitepine and spiperone (Ki = 81 and 31 nM, respectively) and could also be blocked by pretreatment of cells with pertussis toxin. In both cell types, 5-HT failed to stimulate adenylyl cyclase through the expressed receptors. In HeLa cells, 5-HT also stimulated phospholipase C (approximately 40-75% stimulation of formation of inositol phosphates). Again, this effect was inhibited by metitepine. However, the EC50 of 5-HT was considerably higher (approximately 3.2 microM) than that found for inhibition of adenylyl cyclase. Both pathways were demonstrated to be similarly affected by pertussis toxin. These findings indicate that like the M2 and M3 muscarinic cholinergic receptors, the 5-HT1A receptor can couple to multiple transduction pathways with varying efficiencies via pertussis toxin-sensitive G-proteins. The lack of stimulation of cAMP formation by this 5-HT1A receptor may suggest the existence of another pharmacologically closely related receptor.
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PMID:Effector coupling mechanisms of the cloned 5-HT1A receptor. 254 39

The possibility that thrombin-induced platelet reactivity could occur via both a receptor-related and a proteolytic process was examined. Thrombin elicited the formation of considerably more [32P]phosphatidic acid (an index of phospholipase C catalysed phosphoinositide metabolism) than did platelet activating factor, 5-hydroxytryptamine, ADP, and the thromboxane A2 analogue EP171, when these agents were added either alone or in combination. Co-addition of thrombin and EP171 did not evoke significantly more [32P]phosphatide acid than did thrombin alone. The protease inhibitor leupeptin, decreased but did not abolish [32P]phosphatidic acid formation elicited by either thrombin alone or thrombin in combination with EP171. The serine protease, trypsin, stimulated an increase in [32P]phosphatidic acid and this effect was additive with that of EP171. This augmentation by trypsin of EP171-induced [32P]phosphatidic acid formation was inhibited by leupeptin. These results are consistent with the concept that thrombin-induced activation of phospholipase C occurs by two distinct mechanisms: one via proteolysis, which is sensitive to leupeptin, and the other via receptor activation, a process shared by EP171. The individual components of this dual mechanism can be mimicked by the co-addition of a receptor-directed agonist (EP171) and a proteolytic agent (trypsin).
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PMID:Evidence for two mechanisms of thrombin-induced platelet activation: one proteolytic, one receptor mediated. 255 47

The existence of two different functional receptors for 5-hydroxytryptamine (5-HT) was first proposed by Gaddum and Picarelli. Aided by the development of radioligand binding techniques, the heterogeneity of 5-HT receptors has become more apparent in the past ten years. There are three main types of 5-HT receptors: 5-HT1, 5-HT2 and 5-HT3. Moreover, 5-HT1 is heterogenous and can be divided into 5-HT1A, 5-HT1B, 5-HT1C and 5-HT1D subtypes. 5-HT1B is probably related to the 5-HT autoreceptor controlling 5-HT release. Multiple 5-HT receptors are differentially distributed throughout the brain, and the agonist-receptor interaction is altered by physical parameters and chemicals, suggesting that the receptors may be physiologically relevant. Three 5-HT receptor subtypes, 5-HT1A, 5-HT1C and 5-HT2, have been cloned. All three receptors contain approximately 450 amino acids arrayed as seven transmembrane domains. 5-HT1 and 5-HT1A are coupled to adenylate cyclase positively and negatively, respectively, while 5-HT1C and 5-HT2 are coupled positively to phospholipase C. 5-HT1A is also coupled to the opening of K+ channels in hippocampal pyramidal cells. A number of 5-HT-induced physiological responses have been shown to correlate with the 5-HT receptor subtypes. Based on a number of pharmacological studies, it seems likely that the mode of action of certain psychotropic drugs is closely related to the activity of central 5-HT receptors.
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PMID:[5-Hydroxytryptamine receptors]. 255 57

1. The Limulus cardiac ganglion high affinity choline uptake system (HAChUS) was inhibited 40, 51 and 64% following pre-exposure to 10, 100 and 500 microM vinblastine, respectively. 2. In contrast, high affinity uptake of choline in the Limulus corpora pedunculata and abdominal ganglia, tissues in which a cholinergic function has been described, were unaffected. 3. In pulse-chase experiments, the cardiac ganglion was incubated in 0.1 microM [3H]choline for 60 min and then switched to an incubation medium containing 1 mM unlabelled choline for varying periods of time. 4. Under these conditions, a 3-fold increase of radiolabel above basal level was measured in the pellet fraction within 2 hr of post-labelling incubation. 5. Prior exposure of the ganglion to 500 microM vinblastine completely eliminated this increase of radioactivity in the pellet fraction. 6. Treatment of the radiolabelled pellet fraction with phospholipase C resulted in the solubilization of 72% of the radiolabel. 7. Ten (10) microM 5-hydroxytryptamine (5-HT), a concentration previously shown to inhibit spontaneous electrical activity within the cardiac ganglion, resulted in a 40% decrease in high affinity choline uptake in this tissue selectively. 8. These results are consistent with the view that a probable role of the Limulus cardiac ganglion HAChUS is the supply of choline subserving the synthesis of membrane phospholipid. 9. It is further speculated that this membrane phospholipid synthesis may be associated with synaptic vesicle turnover.
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PMID:A vinblastine sensitive high affinity choline uptake system. 256 49

Growth of Chinese hamster lung fibroblasts (CCL39) on thrombin as sole mitogen is dependent on phosphatidylinositol (PI) metabolism and activation of the Na+/H+ antiporter. By modifying a H+ suicide selection developed for the isolation of antiporter mutants in these cells, we enriched for and isolated CCL39 variants deficient in the thrombin mitogenic response (thrombin nongrowers). These mutants retain alternate mitogenic mechanisms and, hence, grow well on media containing serum. When challenged with thrombin, the mutants show decreased, increased, or unchanged levels of inositol phosphates produced as compared with wild type cells. One of the mutants (D1-6b) has decreased inositol phosphates production not only with thrombin but also with serotonin (5-hydroxytryptamine) and AlF4-, suggesting a defect distal to the thrombin receptors. Extracts of this mutant reveal marked decreased phospholipase C activity toward PI. From the different phenotypes of the thrombin nongrowers, it is clear that the selection is general and that mutants with various biochemical defects should lead to a better understanding of the PI cycle as well as of functions essential to mitogenesis.
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PMID:Hamster fibroblasts defective in thrombin-induced mitogenesis. A selection for mutants in phosphatidylinositol metabolism and other functions. 276 25

We have investigated: (a) Phospholipid composition and phosphoinositide-PO4 turnover in rabbit cornea tissues; and (b) the effects of adrenergic and serotonergic agonists on breakdown of phosphoinositides in the rabbit cornea. The data obtained from these studies can be summarized as follows: (1) in the cornea phosphatidylcholine and phosphatidylethanolamine constitute about 55%, phosphatidylinositol (PI) 10%, and phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidic acid (PA) comprise about 1% each of the total phospholipids; (2) incubation of cornea in 32Pi-containing medium resulted in incorporation of radioactivity in tissue phospholipids. The radioactivity was highest in PIP2 (39%), followed by PI (19%), PIP (16%) and PA (5% of the total radioactivity). When compared with stroma and endothelium, the cornea epithelium was most active in phosphoinositide metabolism; (3) addition of norepinephrine (NE) or 5-hydroxytryptamine (5-HT), 200 microM each, to 32P-labeled cornea resulted in a loss of radioactivity in PIP and PIP2 by about 12- and 20%, respectively. Concomitantly, the radioactivity in PA and PI was increased by 44- and 66%, respectively. The effects of the neurotransmitters were time- and concentration-dependent. When added to the cornea labeled with myo [3H] inositol, NE and 5-HT increased the production of labeled myo-inositol phosphates; (4) prazosin (20 microM), but not yohimbine or propranolol, blocked the effects of NE. Similarly, the effects of 5-HT were antagonized by methysergide (20 microM) and ketanserin (10 microM) but not by prazosin. These data demonstrate that NE and 5-HT stimulate phospholipase C-mediated hydrolysis of PIP2 into diacylglycerol (DG) and myo-inositol trisphosphate (IP3). Furthermore, the effects of NE and 5-HT are mediated by alpha 1-adrenergic and 5-HT2 receptors, respectively. It is suggested that IP3, by releasing Ca2+ from ER, and DG, by activating protein kinase C, may function as second-messenger molecules which may participate in agonist-induced functional responses, including chloride transport, in the cornea epithelium.
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PMID:Effects of norepinephrine and 5-hydroxytryptamine on phosphoinositide-PO4 turnover in rabbit cornea. 282 Jul 70

In human platelets, prostaglandin E1 and forskolin inhibit 5-hydroxytryptamine-induced phospholipase C, C-kinase and myosin light-chain kinase activity in a concentration-dependent way. Phospholipase C activation, however, was only partly inhibited, and this at higher concentrations than the protein kinases. Direct activation of the C kinase either by exogenous synthetic diacylglycerol or by 12-O-tetradecanoylphorbol 13-acetate was antagonized by prostaglandin E1 and forskolin. Since C-kinase activation is one of the key events in excitatory signal transduction in the platelets, we suggest that the inhibitory effect of agents that increase platelet cyclic AMP on platelet secretion and aggregation might reside in their capacity to antagonize C-kinase activity.
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PMID:Prostaglandin E1 and forskolin antagonize C-kinase activation in the human platelet. 282 2

The role of a GTP-binding protein in activation of phospholipase C in bovine corneal epithelium was determined by investigating the effects of non-hydrolyzable GTP analog, GTP-gamma-S, and NaF on breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2) in this tissue. GTP-gamma-S (2-50 microM), when introduced into the permeabilized corneal epithelial cells labeled with myo-[3H]inositol, dose-dependently increased the formation of myoinositol trisphosphate (IP3). Other guanine nucleotides and ATP were ineffective. Incubation of 32P-prelabeled corneal epithelium with NaF (2-50 mM) resulted in increased breakdown of PIP2 and increased synthesis of phosphatidic acid. In myo-[3H]inositol-labeled tissue, NaF dose-dependently increased the accumulation of IP3. Microsomal membrane fraction from corneal epithelium was found to contain phospholipase C activity towards endogenous phosphatidylinositol 4-phosphate and PIP2. The enzyme activity was stimulated by Ca2+ (100 microM). Addition of GTP-gamma-S to microsomal fraction containing phosphoinositides which were radiolabeled with 32Pi in situ or with [gamma-32P]ATP in vitro caused a dose dependent hydrolysis of PIP2. These data, taken collectively, suggest that a GTP-binding protein is involved in activation of phospholipase C towards PIP2 in bovine corneal epithelium, and that this guanine nucleotide regulatory protein may serve to couple norepinephrine and 5-hydroxytryptamine receptors to phospholipase C during transmembrane signalling.
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PMID:Guanosine 5'-O-thiotriphosphate and NaF stimulation of phosphatidylinositol 4,5-bisphosphate hydrolysis in bovine corneal epithelium. 284 13


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