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)

Endothelin-1 (ET-1) and ET-3 mRNA have been found in the pancreas. We investigated the ability of ET-1, ET-2, and ET-3 to interact with and alter dispersed rat pancreatic acinar cell function. Radiolabeled ETs bound in a time- and temperature-dependent fashion, which was specific and saturable. Analysis demonstrated two classes of receptors, one class (ETA receptor) had a high affinity for ET-1 but a low affinity for ET-3, and the other class (ETB receptor) had equally high affinities for ET-1 and ET-3. No specific receptor for ET-2 was identified. Pancreatic secretagogues that activate phospholipase C (PLC) inhibited binding of 125I-labeled ET-1 (125I-ET-1) or 125I-ET-3, whereas agents that act through adenosine 3',5'-cyclic monophosphate (cAMP) did not. A23187 had no effect on 125I-ET-1 or 125I-ET-3 binding, whereas the phorbol ester 12-O-tetradecanoylphorbol 13-acetate reduced binding. The effect of cholecystokinin octapeptide (CCK-8) was mediated through its own receptor. Stripping of surface bound ligand studies demonstrated that both 125I-labeled ET-1 and 125I-labeled ET-3 were rapidly internalized. CCK-8 decreased the internalization but did not change the amount of surface bound ligand. Endothelins neither stimulate nor alter changes in enzyme secretion, intracellular calcium, cAMP, or [3H]inositol trisphosphate (IP3). This study demonstrates the presence of ETA and ETB receptors on rat pancreatic acini; occupation of both receptors resulted in rapid internalization, which is regulated by PLC-activating secretagogues. Occupation of either ET receptor did not alter intracellular calcium, cAMP, IP3, or stimulate amylase release.
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PMID:Pancreatic acini possess endothelin receptors whose internalization is regulated by PLC-activating agents. 768 69

The endothelin receptors, ETA and ETB, are G protein-coupled receptors (GPCR) that show distinctively different binding profiles for the endothelin peptides and other ligands. We recently reported that Tyr129 in the second transmembrane region (TM2) of the ETA receptor was critical for subtype-specific ligand binding [Krystek, S.R. et al. (1994) J. Biol. Chem. 269, 12383-12386]. Receptor models indicated that aspartic acids located one helical turn above (Asp133) and below (Asp126) Tyr129 in ETA had their side chains directed toward the putative binding cavity. Similarly in ETB, Asp147 and Asp154 are located one turn below and above His150, the residue that corresponds to Tyr129. Asp126 in ETA and Asp147 in ETB correspond to the highly conserved aspartate present in TM2 of many GPCR that has frequently been shown to be crucial for agonist efficacy. Mutagenesis of Asp126 of the human ETA receptor to alanine resulted in an unaltered affinity for ET-1, a 160-fold increase in ET-3 affinity and a decrease in affinity for the ETA selective naphthalenesulfonamide, BMS-182874. ET-1 activation of phospholipase C was abolished. In addition, despite the gain in binding affinity, ET-3 failed to activate phospholipase C, suggesting that Asp126 is required for signal transduction. Mutagenesis of Asp133 to alanine indicated that it was critical only for the binding of BMS-182874. In the ETB receptor, mutation of His150 to alanine or tyrosine indicated that it plays a minor role in ETB subtype-selective ligand binding; mutation of the aspartates in TM2 of ETB did not alter ligand binding. As in the Asp126 Ala ETA variant, ET-1 and ET-3 failed to increase intracellular levels of inositol phosphates in the Asp147Ala ETB mutant. Taken together, these data support the hypothesis that Asp126 and Asp133 flanking Tyr129 in TM2 of the ETA receptor play a role in defining ETA subtype-selective ligand binding but Asp147 and Asp154 that flank the His150 in TM2 of the ETB receptor do not. Furthermore, these data indicate that Asp126 in ETA and Asp147 in ETB are important for transmembrane signaling via phospholipase C.
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PMID:Aspartate mutation distinguishes ETA but not ETB receptor subtype-selective ligand binding while abolishing phospholipase C activation in both receptors. 769 31

The aim of the present study was to characterize endothelin (ET)-receptors in human myometrial cells in culture. 125I-labeled ET-1 binding to myometrial cells was specific and saturable, with a dissociation constant of 64.2 +/- 12.8 pM. Competition binding studies showed the following order of potency: ET-1 > ET-3, which is consistent with the presence of the ETA receptor subtype. FR-139317 and BQ-123, two ETA antagonists, both inhibited 125I-ET-1 binding. BQ-123 only elicited a partial inhibition. The fraction resistant to BQ-123 did not represent the ETB receptor subtype, since no specific 125I-ET-3 binding could be detected. ET-1 and ET-3 were found to stimulate [3H]inositol phosphate (IP) accumulation in cultured myometrial cells, with corresponding half-maximal effective concentration values of 0.26 +/- 0.04 and 87 +/- 17 nM, respectively. Both ETA antagonists inhibited ET-1-induced accumulation of [3H]IP. BQ-123 was only a partial inhibitor, whereas FR-139317 totally suppressed ET-1-stimulated production of [3H]IP. We conclude that human myometrial cells in culture exclusively possess ETA receptor subtypes coupled to phospholipase C.
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PMID:Characterization of type A endothelin receptors in cultured human myometrial cells. 776 34

This study was performed to examine the effects of endothelin (ET)-1, ET-2, and ET-3 on renin secretion from cultured mouse renal juxtaglomerular (JG) cells. Although different ETs had no consistent effect on basal renin secretion, they equipotently inhibited adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated renin release with a concentration of approximately 3 nM inhibiting 50% of maximal response. ETs did not significantly affect renin release stimulated by the nitric oxide donor sodium nitroprusside (100 microM) or that stimulated by low [2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] or high (3 mM CaCl2) extracellular calcium. The inhibitory effect of ETs on cAMP-dependent renin secretion was abolished by lowering extracellular calcium concentration to the nanomolar range. However, the action of ETs was not changed by the ETA receptor antagonist BQ-123 (100 nM) and was mimicked by ETB receptor agonists IRL-1620 (1 microM), sarafotoxin S6b (1 microM), and [Ala1,3,11,15]ET-1 (1 microM). All ETs induced calcium oscillations in JG cells that were dependent on extracellular calcium and were associated with prominent calcium-activated chloride currents. These findings suggest that ETs inhibit rather selectively the cAMP-activated pathway of renin secretion through a calcium-sensitive process. The action of ETs on renal JG cells appears to be mediated via ETB receptors and is presumably related to activation of phospholipase C and subsequent events.
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PMID:Effects of endothelins on renin secretion from isolated mouse renal juxtaglomerular cells. 784 Feb 46

Endothelin is a peptide with potent biologic effects in vascular and nonvascular cells. Its effects are mediated by two receptors, ETA and ETB, and possibly also by a third receptor, ETC. In vascular smooth muscle cells, endothelin causes profound contraction and also has proliferative effects, mainly through activation of ETA but also through ETB receptors. Activation of endothelin receptors on vascular smooth muscle explains the profound vasoconstriction observed in isolated blood vessels as well as with infusion of the peptide in vivo. Endothelial cells can express ETB receptors linked to the formation of nitric oxide or prostacyclin. Activation of these receptors leads to the transient vasodilation observed with intravascular infusion of the peptide. In vascular smooth muscle, activation of endothelin receptors stimulates phospholipase C, with concomitant formation of inositol triphosphate and diacylglycerol. These events lead to the release of intracellular calcium and initiation of contraction. In addition, endothelin can activate voltage-operated calcium channels via Gi proteins, thereby increasing influx of extracellular calcium. The later phenomenon may explain the ability of calcium antagonists to inhibit endothelin-induced contractions. Normally, circulating endothelin levels, as well as production of the peptide in isolated blood vessels, are rather low due to the absence of stimuli and the presence of potent inhibitory mechanisms. Important stimulators of endothelin production are thrombin, angiotensin II, arginine vasopressin, and transforming growth factor-beta, as well as certain cytokines and physicochemical factors such as hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Endothelin, endothelin receptors, and endothelin antagonists. 785 Apr 17

Endothelins (ETs) (ET-1, ET-2, and ET-3), a family of 21-amino acid peptides, mediate a host of biological responses by binding to specific cell surface receptors termed ETA and ETB. Because a role for ET in bone remodeling has been suggested, the present study was undertaken (a) to characterize ET receptors and their responses in the rat osteosarcoma cell line ROS 17/2.8 and (b) to study their regulation by 1,25-dihydroxy-vitamin D3. Binding studies using 125I-ET-1 (a nonselective agonist) and 125I-IRL-1620 (an ETB receptor-selective agonist) indicated that these cells display high affinity ETA and ETB receptors in the ratio of 3:1. Addition of ET-1 or sarafotoxin 6c to myo-[3H]inositol-labeled cells resulted in an increase in inositol phosphate accumulation as well as in intracellular Ca2+ release, suggesting that these receptors are coupled to phospholipase C. In addition, ET-1 but not sarafotoxin 6c induced a modest increase in the expression of osteocalcin protein that was completely blocked by BQ123 (an ETA receptor-selective antagonist), indicating that activation of ETA receptors plays a role in the induction of osteocalcin. Treatment of ROS osteoblasts with 10 nM 1,25-dihydroxy-vitamin D3 for 14 hr resulted in a significant (> 50%) decrease in 125I-ET-1 and 125I-IRL-1620 binding. This decrease in binding was shown to be due to a decrease in the number of ET receptors, with no change in affinity. Although both ETA and ETB receptors were down-regulated in response to 1,25-dihydroxy-vitamin D3, only ETA receptor mRNA levels were significantly decreased, with very little change in ETB mRNA levels. These data indicate that ROS osteoblasts display both ETA and ETB receptors that are functional. Induction of osteocalcin was primarily mediated by ETA receptors, and these receptors were also down-regulated at the mRNA level by 1,25-dihydroxy-vitamin D3.
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PMID:Identification and characterization of endothelin receptors on rat osteoblastic osteosarcoma cells: down-regulation by 1,25-dihydroxy-vitamin D3. 787 34

The coupling of two endothelin receptor subtypes (ET(A) and ETB) to several types of guanine-nucleotide-binding regulatory protein (G protein) was examined. Two subtypes of receptor cDNAs were transfected alone or together with four different G protein alpha subunit cDNAs in COS-7 cells. In ET(A) receptor-transfected cells, endothelin-1 (ET-1) activated phosphatidylinositol-specific phospholipase C as measured by the production of phosphatidylinositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. ETB-receptor-transfected cells also produced Ins(1,4,5)P3 on stimulation by ET-1. The ET-1-induced production of Ins(1,4,5)P3 was markedly higher in G alpha q-cotransfected or G alpha 11-cotransfected cells than in cells transfected with each receptor alone. ET-1 also stimulated production of cAMP in ET(A) or ETB receptor-transfected cells. The production of cAMP was synergistically amplified by G alpha s co-transfection with each receptor. In contrast, when G alpha i2 was co-transfected with the ET(A) or ETB receptor, ET-1 displayed an inhibitory action on forskolin-stimulated cAMP accumulation. Pertussis-toxin treatment of the G alpha i2-transfected cells resulted in abolition of the endothelin-induced inhibition of cAMP accumulation. These observations indicate that both ET(A) and ETB receptors are able to couple to Gq, G11, Gs and Gi2, and suggest that endothelin receptors stimulate multiple effectors via several types of G protein simultaneously. The overall effects induced by endothelin may differ in cell types depending on the level of expression of each G-protein subtype in the cell.
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PMID:Molecular identification of guanine-nucleotide-binding regulatory proteins which couple to endothelin receptors. 788 89

Endothelin (ET) binding sites and phosphoinositide hydrolysis induced by ET peptides were studied in the nonpregnant human myometrium. Saturation binding experiments revealed that the proportion of [125I]ET-1 binding sites was 4-fold higher than that of [125I]ET-3 binding sites, whereas Kd values were not significantly different. In competition binding studies, unlabeled peptides displaced [125I]ET-1 binding with the following order of affinity ET-1 > sarafotoxin 6b > ET-3 >> sarafotoxin 6c, whereas very similar Ki values were obtained with the four peptides for the displacement of [125I]ET-3 binding. Approximately 75% of [125I]ET-1 binding sites exhibited high affinity to BQ 123 ([cyclo(D-Trp,D-Asp,L-Pro,D-Val,L-Leu)]), an ETA selective antagonist. ET-1 elicited a time-dependent accumulation of [3H]inositol phosphates in myometrial explants prelabeled with myo-[3H]inositol. All the peptides examined, ET-1, ET-3, sarafotoxin 6b and sarafotoxin 6c were able to induce phosphoinositide hydrolysis in a dose-dependent manner, ET-1 being more potent than ET-3 with corresponding EC50 values of 32 +/- 12 and 441 +/- 37 nM, respectively. Sarafotoxin 6c induced a moderate stimulation of inositol phosphates accumulation. ET-1- and ET-3-induced accumulation of [3H]inositol phosphates was (40-45%) inhibited in part by 100 microM BQ 123, whereas sarafotoxin 6c response was not affected by the ETA-antagonist. All these results indicate the presence of ETA and ETB receptors coupled to phospholipase C in human myometrium. Although ET-1 and ET-3 bind to both subtypes, sarafotoxin 6c only interacts with the ETB subtype.
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PMID:Endothelin receptors: binding and phosphoinositide breakdown in human myometrium. 793 9

The existence of vasoconstrictive factors originating from the endothelium was confirmed by the description of endothelin, a 21-amino-acid peptide derived from a series of precursors, preproendothelin and a 38-amino-acid big endothelin. Three isoforms of endothelin, endothelin-1, -2 and -3, and 3 receptors (ETA, ETB and ETC) have been described and cloned. The cellular mode of action of endothelin seems to involve the modulation of intracellular calcium (through inositol trisphosphate, diacylglycerol and phospholipase C) and activation of calcium channels. The effects of endothelin are predominantly on the cardiovascular system. Its major effect is vasoconstriction, both systemic and pulmonary, with additional positive chronotropic and inotropic effects on the heart. It has also been implicated in homeostatic regulation of kidney microcirculation, and has powerful mitogenic effects on fibroblasts and smooth muscle cells. Many additional effects have been described on the endocrine system and on other systems. However, the clinical relevance of such effects is uncertain. Increased plasma endothelin levels have been reported in many diseases, but as yet it is not certain whether they are a cause or a consequence of the pathology. Pathologies most probably related to endothelin dysfunction are the vasospastic diseases, especially vasospasm after subarachnoid haemorrhage. Endothelin could be implicated to a lesser measure in diseases typical of the elderly population, such as hypertension or atherosclerosis. Drugs are being developed which act on endothelin metabolism, the most promising of which appear to be the inhibitors of endothelin converting enzyme and endothelin receptor antagonists. Some already existing drugs, such as calcium channel blockers or angiotensin converting enzyme inhibitors, probably act at least in part by interfering with endothelin metabolism or effects.
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PMID:Endothelins. A potential target for pharmacological intervention in diseases of the elderly. 819 96

We have demonstrated in liver from male rats that both endothelin A (ETA) and ETB receptors coexist in equal proportion and that ETA receptors mediate a calcium-dependent activation of glycogenolysis. We describe here a sex difference in endothelin action in hepatocytes because, in female rats, 80% of the ET receptors are of ETB type and, accordingly, activation of glycogenolysis is an ETB-mediated process (EC50 = 0.03 pM). ET-1 stimulation of glycogenolysis in female rats was consecutive to activation of phosphatidylinositol 4,5-bisphosphate hydrolysis (EC50 = 0.03 pM) and to inhibition of the calcium extrusion pump (IC50 = 0.03 pM) in plasma membranes, with ET-1 approximately sarafotoxin S6C approximately ET-3. Endothelin regulation of each effector was potentiated by GTP gamma S. ET-1 did not stimulate adenylyl cyclase activity. To identify the nature of the guanine nucleotide regulatory proteins (G protein(s)) coupling ETB receptors to each effector, we used antibodies against the COOH terminus of different G protein alpha subunits. Antibodies reactive with Gs alpha (RM) blocked ET-1 inhibition of the calcium pump, while they did not affect ET-1 stimulation of phospholipase C. Antibodies reactive with Gq alpha (QL) dose-dependently antagonized stimulation of phospholipase C by ET-1 and vasopressin, without affecting ET-1 inhibition of the calcium pump. Antibodies reactive with Gi1 alpha/Gi2 alpha (AS) had no effect on either system. We conclude that the calcium signal provoked by endothelins in hepatocyte is not only consecutive to activation of phospholipase C but also to inhibition of the plasma membrane calcium pump, each effector being coupled to ETB receptors by different G proteins, Gq, and Gs.
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PMID:Coupling of endothelin B receptors to the calcium pump and phospholipase C via Gs and Gq in rat liver. 829 32


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