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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)

PC12 cells, a rat pheochromocytoma cell line, has been reported to release norepinephrine in response to extracellular ATP in the presence of extracellular Ca2+. The potency order of ATP analogues was adenosine 5'-O-(3-thiotriphosphate) greater than ATP greater than adenosine 5'-O-(1-thiotriphosphate) = 2-methylthioadenosine 5'-triphosphate (MeSATP) greater than 2'- and 3'-O-(4-benzoyl-benzoyl)ATP (BzATP) greater than ADP greater than 5-adenylylimidodiphosphate. Adenosine 5'-O-(2-thiodiphosphate), beta, gamma-methyleneadenosine 5'-triphosphate, AMP and adenosine were inactive. The ATP action in the absence of extracellular Ca2+, suggests a small but appreciable contribution of intracellular Ca2+ mobilization, for norepinephrine release. However, for some ATP derivatives, like BzATP, almost no contribution of the phospholipase C-Ca2+ pathway is suggested, based on their low activity in inositol phosphates production. To identify the ATP-receptor protein, PC12 cell membranes were photoaffinity-labeled with [32P]BzATP. SDS-PAGE analysis showed that a 53-kDa protein labeling was inhibited by ATP and its derivatives, as well as by P2-antagonists, suramin and reactive blue 2, which inhibit the nucleotide-induced norepinephrine release. The inhibitory activity of the nucleotides was, in parallel with their potency, to induce norepinephrine release. Despite their inability to release norepinephrine, GTP and GTP gamma S inhibited the BzATP labeling, suggesting the participation of a putative G protein in the ATP-receptor-mediated actions. We suggest that the 53-kDa protein on the PC12 cell surface is an ATP receptor, which mediates the norepinephrine release, depending, mainly, on extracellular Ca2+ gating.
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PMID:Characterization of ATP receptor which mediates norepinephrine release in PC12 cells. 132 38

Extracellular ATP has been shown to induce intracellular Ca2+ mobilization and adenylate cyclase inhibition via P2 purinoceptors in several species of cells. Now we found that in calf vascular smooth muscle cells the addition of ATP to the medium did not induce inhibition but stimulation of cyclic AMP accumulation, in addition to stimulation of inositol phosphate production. Adenosine and AMP also induced cyclic AMP accumulation but their efficacy was much less than that of ATP. The ATP action was not influenced by the presence of either adenosine deaminase or of an ATP regenerating system, whereas the AMP action was increased by the regenerating system. The results indicate that the cyclic AMP accumulation by ATP is due to ATP itself but neither to adenosine nor to AMP, both of which are produced from ATP. ATP receptor coupled to the cyclic AMP generation was shown to be different from that coupled to phospholipase C based on the difference in the potency order of the receptor agonists and in the sensitivity of P2 receptor agonists to 8-cyclopentyl-1,3-dipropylxanthine (CPX)- and suramin-induced antagonism. We conclude that in the aortic smooth muscle cells a novel P2-type receptor directly coupled to adenylate cyclase activation exists in addition to the previously known P2 receptor linked to phospholipase C activation.
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PMID:P2 purinoceptor-mediated cyclic AMP accumulation in bovine vascular smooth muscle cells. 133 Jun 37

Macrophages express two distinct types of nucleotide (P2 purinergic) receptors for extracellular ATP: one type induces a Ca(2+)-mobilizing response via the activation of phosphatidylinositol-phospholipase C (PI-PLC) while the second type induces the rapid formation of nonselective pores which are permeated by ions and small (< 1 kDa) organic molecules. We have confirmed the presence of these two ATP receptor types in the BAC1.2F5 murine macrophage cell line and have identified 3'-O-(4-benzoyl)benzoyl-ATP (BzATP) as a selective and potent agonist for the so-called P2z or pore-forming ATP receptor type. Several lines of evidence indicated that occupation of these P2z receptors is also accompanied by a rapid and large increase in the activity of a phosphatidylcholine-selective phospholipase D (PLD) effector enzyme. In cells metabolically labeled with [3H]oleic acid or [3H]glycerol and stimulated in the presence of ethanol, ATP and BzATP induced a severalfold increase in the rate and extent of [3H]phosphatidylethanol (PEt) accumulation. These responses were stimulated only by ATP, BzATP, and ATP gamma S (adenosine 5'-O-(3-thiotriphosphate) with the rank order of potency: BzATP >> ATP > ATP gamma A; there was no response to other adenine nucleotides or to non-adenine nucleotides. Significantly, the ability of P2z receptor agonists to stimulate this PLD activity was not dependent on the presence of extracellular [Ca2+] or elevation of cytosolic [Ca2+]. The inability of ionomycin, gramicidin, digitonin, UTP, platelet-activating factor, or phorbol ester to quantitatively mimic these nucleotide effects suggested that activation of this PLD by P2z receptor agonists was not a secondary response due to: 1) enhanced Ca2+ influx; 2) membrane depolarization; 3) nonselective permeabilization of the plasma membrane; 4) stimulation of Ca(2+)-mobilizing ATP receptors; 5) stimulation of a primary PI-PLC pathway; or 6) activation of protein kinase C. These findings suggest that activation of a novel PLD-based signaling pathway may play an important role in the modulation of macrophage function by pore-forming P2z receptors for extracellular ATP.
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PMID:A novel pathway for the activation of phospholipase D by P2z purinergic receptors in BAC1.2F5 macrophages. 133 Oct 96

Extracellular ATP and UTP caused a rapid formation of InsP3, with similar kinetics and dose-dependences. ITP also displayed strong agonistic properties in terms of InsP3 production, whereas CTP was almost inactive. Pretreatment of the cells with pertussis toxin attenuated ATP- and UTP-stimulated InsP3 generation to a comparable extent, indicating that both nucleotides couple to phospholipase C by a pertussis-toxin-sensitive G-protein. Short-term (15 min) treatment of the cells with phorbol 12-myristate 13-acetate (PMA) produced a dose-dependent inhibition of ATP- and UTP-induced InsP3 formation. Furthermore, down-regulation of protein kinase C by long-term (24 h) exposure of the cells to PMA resulted in a comparable potentiation of phosphoinositide hydrolysis by both nucleotides. Preincubation of mesangial cells with ATP or UTP caused a pronounced cross-desensitization of subsequent nucleotide-stimulated InsP3 production. ATP and UTP displayed no additivity in terms of InsP3 formation, when used at maximally effective concentrations. In contrast, the peptide hormone angiotensin II interacted in an additive manner with either nucleotide in stimulating phosphoinositide hydrolysis. Reactive Blue 2, a putative P2y-purinoceptor antagonist, caused a rightward shift of both the ATP and UTP dose-response curves. However, since 2-methylthio-ATP was only a partial agonist in stimulating InsP3 formation, the mesangial-cell ATP receptor appears to be different from a classic P2y-receptor. In summary, these results provide no evidence for separate purino- and pyrimidino-ceptors on mesangial cells. In contrast, ATP and UTP may use a common nucleotide receptor for transducing their signals in mesangial cells.
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PMID:Comparison of extracellular ATP and UTP signalling in rat renal mesangial cells. No indications for the involvement of separate purino- and pyrimidino-ceptors. 217 64

The relationship between phospholipase A2 and C activation and secretion was investigated in intact human neutrophils and differentiated HL60 cells. Activation by either ATP or fMetLeuPhe leads to [3H]arachidonic acid release into the external medium from prelabelled cells. This response was inhibited when the cells were pretreated with pertussis toxin. When the [3H]arachidonic acid-labelled cells were stimulated with fMetLeuPhe, ATP or Ca2+ ionophore A23187, and the lipids analysed by t.l.c., the increase in free fatty acid was accompanied by decreases in label from phosphatidylinositol and phosphatidylcholine. Moreover, incorporation of label into triacylglycerol and to a lesser extent phosphatidylethanolamine was evident. Activation of secretion was evident with ATP and fMetLeuPhe but not with A23187. The pharmacological specificity of the ATP receptor in HL60 cells was investigated by measuring secretion of beta-glucuronidase, formation of inositol phosphatases and release of [3H]arachidonic acid. External addition of ATP, UTP, ITP, adenosine 5'-[gamma-thio]triphosphate (ATP[S]), adenosine 5'-[beta gamma-imido]triphosphate (App[NH]p), XTP, CTP, GTP, 8-bromo-ATP and guanosine 5'-[gamma-thio]triphosphate (GTP[S]) to intact HL60 cells stimulated inositol phosphate production, but only the first five nucleotides were effective at stimulating secretion or [3H]arachidonic acid release. In human neutrophils, addition of ATP, ITP, UTP and ATP[S] also stimulated secretion from specific and azurophilic granules, and this was accompanied by increases in cytosolic Ca2+ and in [3H]arachidonic acid release. The addition of phorbol 12-myristate 13-acetate (PMA; 1 nM) prior to the addition of either fMetLeuPhe or ATP led to inhibition of phospholipase C activity. In contrast, this had no effect on phospholipase A2 activation, whilst secretion was potentiated. Phospholipase A2 activation by either agonist was dependent on an intact cell metabolism, as was secretion. It is concluded that (1) activation of phospholipase C does not always lead to activation of phospholipase A2, (2) phospholipase A2 is coupled to the receptor independently of phospholipase C via a pertussis-toxin-sensitive G-protein and (3) for secretion to take place, the receptor has to activate both phospholipases C and A2.
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PMID:The receptors for ATP and fMetLeuPhe are independently coupled to phospholipases C and A2 via G-protein(s). Relationship between phospholipase C and A2 activation and exocytosis in HL60 cells and human neutrophils. 251 11

ATP produced whole-cell potassium currents with a latency of 200 msec in cultured smooth muscle cells of bovine brain arteries. The currents were evoked via an ATP receptor linked to a pertussis toxin-insensitive G-protein, which is not involved in phospholipase C (PLC)-mediated signal transduction, and were not regulated by protein kinase A or C. In the cell-attached patches, ATP elicited single channel currents with two major classes of slope conductances and these currents were again induced within 100 msec after bath-application of ATP outside the patch pipette. In addition, ATP enhanced intracellular free Ca2+ concentration ([Ca2+]i) with no initiation time in the presence and absence of extracellular Ca2+, and this enhancement was not blocked by a PLC inhibitor. These results, thus, suggest that the activation of the potassium channel and the enhancement of [Ca2+]i induced by ATP may be caused by a direct action of the G-protein beta gamma subunits.
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PMID:Dual effects of ATP on the potassium channel and intracellular Ca2+ release in smooth muscle cells of the bovine brain arteries. 748 33

The mechanisms of activation of cytoplasmic phospholipase A2 (cPLA2) are complex and incompletely defined. In Chinese hamster ovary (CHO) cells, receptor stimulation of cPLA2 is due to the interaction of pathways involving the alpha subunits of at least two guanine-nucleotide-binding (G) proteins, G alpha i2 and G alpha q. Activation of cPLA2 is inhibited by pertussis toxin and G alpha i2 mutants. In addition, activation of phospholipase C via G alpha q results in increased intracellular calcium ([Ca2+]i) and activation of protein kinase C, both of which interact with and activate cPLA2. The present study was undertaken to analyze the mechanism of interaction of G alpha i2 with the phospholipase-C-stimulated pathway in the activation of cPLA2. We addressed this question using a dominant negative G alpha i2 mutant, [G203T]G alpha i2, in which Gly203 is mutated to Thr. [G203T]G alpha i2 inhibits ATP receptor activation of cPLA2. The effect of [G203T]G alpha i2 was specific to G alpha i2-activated pathways, as shown by its lack of effect on other purinergic receptor stimulated pathways: ATP stimulation of [Ca2+]i or mitogen-activated protein kinase phosphorylation is unaltered by [G203T]G alpha i2. We addressed the possibility that the activation of cPLA2 by Ca2+ and/or protein kinase C is dependent on G alpha i2. Activation of cPLA2 by the Ca2+ ionophore, ionomycin, was inhibited by 61 +/- 9% (n = 5) in [G203T]G alpha i2-expressing cells; however the ionomycin-induced [Ca2+]i rise was unaffected by [G203T]G alpha i2. Thus, [G203T]G alpha i2. specifically inhibits Ca2+ activation of cPLA2. In contrast, activation of cPLA2 via protein kinase C by phorbol 12-myristate 13-acetate was unaffected by [G203T]G alpha i2. Our results demonstrate that Ca2+ but not phorbol ester activation of cPLA2 in CHO cells is G alpha i2-dependent. The possibility is discussed that G alpha i2 is downstream of Ca2+ but upstream of protein kinase C activation of cPLA2.
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PMID:The guanine-nucleotide-binding protein subunit G alpha i2 is involved in calcium activation of phospholipase A2. Effects of the dominant negative G alpha i2 mutant, [G203T]G alpha i2, on activation of phospholipase A2 in Chinese hamster ovary cells. 760 Oct 96

The effects of ATP, U-73122, apyrase, and saline shear stress on [Ca2+]i homeostasis were studied in fura-2 loaded, mouse fibroblast cells (L929), both in suspension and plated on glass. Release of internal Ca2+ was induced by ATP, via a receptor identified pharmacologically as a P2U type. In single cells, low concentrations of ATP evoked [Ca2+]i oscillations. These events were blocked by the putative phospholipase C inhibitor, U-73122 (but not by the inactive analog U-73343) and by the ATP/ADPase, apyrase. In addition, both these agents reduced the [Ca2+]i of unstimulated cells, especially after stirring, and blocked spontaneously occurring [Ca2+]i oscillations, which suggested an already activated state of the ATP receptor, independent from exogenous stimulations. Moreover, it was found that stirring of the cells was correlated with a steady accumulation of inositol phosphates, also blockable by apyrase, and that [Ca2+]i mobilization could be induced by puffs of saline in single cells. The transition to a Ca(2+)-free environment also provoked [Ca2+]i oscillations, most likely via the increase in ATP4- concentration. This evidence suggests that endogenous ATP is released from L fibroblasts in response to fluid shear stress, and this results in an autocrine, tonic up-regulation of the phosphoinositide signaling system and an ensuing alteration in Ca2+ homeostasis. Up until now, such a response to shear stress was believed to be unique to endothelial cells.
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PMID:Shear stress-induced [Ca2+]i transients and oscillations in mouse fibroblasts are mediated by endogenously released ATP. 787 11

Extracellular ATP (a purine nucleotide) and UTP (a pyrimidine nucleotide) both activated phospholipase C with a similar potency and efficacy; however, in contrast to ATP which induced a remarkable norepinephrine release, UTP-induced norepinephrine release was small in PC12 cells, a rat pheochromocytoma cell line. ATP, its derivatives (2-methylthioadenosine 5'-triphosphate (MeSATP) and 2'- and 3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP)) and UTP increased intracellular Ca2+ in the presence of 2 mM extracellular Ca2+ with the potency order of ATP > MeSATP > BzATP = UTP. Under the low extracellular Ca2+ conditions, the Ca2+ response to purine nucleotides was markedly reduced, but the UTP response was not. The [32P]BzATP labeling of a 53-kDa putative ATP receptor coupled to a channel system (Majid, M.A., Okajima, F., and Kondo, Y. (1992) Biochim. Biophys. Acta 1136, 283-289) was markedly inhibited by ATP, but not by UTP. These results suggest that UTP activates the phospholipase C-Ca2+ system through a receptor different from the 53-kDa ATP receptor.
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PMID:UTP activates phospholipase C-Ca2+ system through a receptor different from the 53-kDa ATP receptor in PC12 cells. 836 17

We have recently identified gonadotropes as target cells for ATP action via ATP receptors of the P2U subtype. The present studies have used gonadotrope-derived alpha T3-1 cells to examine the possible signaling mechanisms subserving ATP action in gonadotropes. Addition of ATP produced a biphasic intracellular Ca2+ (Ca2+i) response: a transient spike followed by a small plateau. Removal of extracellular Ca2+ or depolarization with KCl abolished the plateau but had no effect on the spike. The plateau was also blocked by cadmium or nifedipine but not nickel. Pretreatment with GnRH or thapsigargin but not ryanodine inhibited the subsequent Ca2+i response to ATP. Pertussis toxin had no effect on ATP-induced Ca2+i response, whereas the phospholipase C inhibitor U73122 reduced the response. These observations suggest that the Ca2+i response is mediated by a pertussis toxin-insensitive and phospholipase C-coupled G-protein and reflects Ca2+ release from the GnRH- and thapsigargin-sensitive Ca2+ pool followed by Ca2+ influx through high voltage-gated Ca2+ channels. Activation of these ATP receptors had no apparent effects on the cAMP and cGMP signaling systems. Treatment with ATP-gamma S caused the translocation of protein kinase C (PKC) epsilon but not PKC zeta and PKC alpha to the particulate fraction. These data not only characterize the ATP receptor-mediated intracellular signaling in alpha T3-1 cells and render further evidence for a mediator role for nucleotides in gonadotrope function but also provide the first direct demonstration of PKC translocation by ATP receptors.
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PMID:Effects of extracellular nucleotides in the pituitary: adenosine triphosphate receptor-mediated intracellular responses in gonadotrope-derived alpha T3-1 cells. 853 20


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