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)

1. Adenosine 5'-diphosphate (ADP) is a physiologically important mediator, being released from damaged cells and from aggregating platelets. It acts on platelets to cause aggregation via a purinoceptor ('P2T-purinoceptor') at which adenosine 5'-triphosphate (ATP) is a competitive antagonist; however, the way in which it does so is not fully understood. 2. ADP activates a G12 protein, is a weak activator of phospholipase C but causes calcium mobilization from internal stores, and also inhibits adenylate cyclase. It seems likely that these effects are mediated by a single receptor but this is still unclear. 3. ADP also causes a rapid calcium influx which has the characteristics of a receptor-operated channel, and it has been suggested that this is due to a P2X1 receptor. This suggests the presence of at least two types of receptor responding to ADP, one G protein coupled and one a cation channel, and raises questions about the role of ATP in platelet function. 4. Adenosine acts via an A2a receptor to stimulate adenylate cyclase in platelets, and this nonselectively inhibits platelet activation. As ADP released from platelets is broken down to adenosine by ectonucleotidases on endothelial cells, this may provide an important mechanism for limiting inappropriate platelet aggregation in an intact blood vessel.
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PMID:Purinoceptors and platelet aggregation. 913 14

Adenosine 5'-triphosphate (ATP) and/or related nucleotides act at both ionotropic (P2X) and metabotropic (P2Y) receptors. P2X receptor subunits (P2X1-P2X7) form ligand-gated cation channels, as homomultimers or heteromultimers. Recent work indicates that P2X3 subunits participate in channels expressed by nociceptive sensory neurons, and that the second of the two transmembrane domains of each subunit contributes to the ion permeation pathway. P2X7 subunits form large cytolytic pores in addition to cation channels; they have been found in macrophages and brain microglia. P2Y receptors form a distinct subset of G-protein-coupled receptors; most couple through G proteins to phospholipase C, but inhibition of adenylate cyclase and N-type Ca2+ channels, and activation of K+ channels also occurs. Expressed P2Y receptors have generally been distinguished pharmacologically by the rank order of effectiveness of agonists; some prefer pyrimidines to purines. Recent studies suggest that it is important to use purified nucleotides in such classifications. Several P2Y receptors have a very widespread tissue distribution.
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PMID:Nucleotide receptors. 923 9

ADP is an important platelet agonist causing shape change from smooth discoid shape to spiculated spheres and platelet aggregation. However, the molecular mechanisms involved in ADP-induced platelet activation have not been elucidated. We demonstrated earlier the existence of two distinct ADP receptors on platelets, one coupled to phospholipase C, P2TPLC, and the other to inhibition of adenylyl cyclase, P2TAC (Daniel, J. L., Dangelmaier, C., Jin, J., Ashby, B., Smith, J. B., and Kunapuli, S. P. (1998) J. Biol. Chem. 273, 2024-2029), in addition to the previously described P2X1 receptor. Here we report the cloning of a cDNA clone encoding the P2Y1 receptor from a human platelet cDNA library by homology screening with radiolabeled P2Y1-P2Y6 receptor cDNAs. ADP or 2-methyl(thio)-ADP-induced intracellular calcium increases were inhibited by the P2Y1 receptor-specific antagonists, adenosine 3'-phosphate 5'-phosphosulfate (A3P5PS), adenosine 3'-phosphate 5'-phosphate (A3P5P), and adenosine 2'-phosphate 5'-phosphate (A2P5P), in a concentration-dependent manner, but not by ARL 66096 or alpha, beta-MeATP. A3P5PS, A3P5P, and A2P5P also inhibited the shape change of aspirinated platelets induced by 10 microM ADP or 3 microM 2-methyl-(thio)-ADP in a concentration-dependent manner, with complete inhibition occurring at 300 microM. On the other hand ARL 66096 (100 nM), a potent P2TAC antagonist and alpha, beta-methylene-ATP (40 microM), a P2X1 receptor agonist, had no effect on ADP-induced platelet shape change. On the contrary, ADP-induced inhibition of adenylyl cyclase was blocked by ARL 66096, but not by alpha, beta-MeATP or the P2Y1 receptor-specific antagonists, A3P5PS, A3P5P, or A2P5P. These results demonstrate the role of the P2Y1 receptor in ADP-induced platelet shape change and calcium mobilization and support the idea that several P2 receptors are involved in the regulation of different aspects of platelet stimulus-response coupling.
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PMID:Molecular basis for ADP-induced platelet activation. II. The P2Y1 receptor mediates ADP-induced intracellular calcium mobilization and shape change in platelets. 944 40

Analogues of the P2 receptor antagonists pyridoxal-5'-phosphate and the 6-azophenyl-2',4'-disulfonate derivative (PPADS), in which the phosphate group was cyclized by esterification to a CH2OH group at the 4-position, were synthesized. The cyclic pyridoxine-alpha4, 5-monophosphate, compound 2 (MRS 2219), was found to be a selective potentiator of ATP-evoked responses at rat P2X1 receptors with an EC50 value of 5.9 +/- 1.8 microM, while the corresponding 6-azophenyl-2',5'-disulfonate derivative, compound 3 (MRS 2220), was a selective antagonist. The potency of compound 3 at the recombinant P2X1 receptor (IC50 10.2 +/- 2.6 microM) was lower than PPADS (IC50 98.5 +/- 5.5 nM) or iso-PPADS (IC50 42.5 +/- 17.5 nM), although unlike PPADS its effect was reversible with washout and surmountable. Compound 3 showed weak antagonistic activity at the rat P2X3 receptor (IC50 58.3 +/- 0.1 microM), while at recombinant rat P2X2 and P2X4 receptors no enhancing or antagonistic properties were evident. Compounds 2 and 3 were found to be inactive as either agonists or antagonists at the phospholipase C-coupled P2Y1 receptor of turkey erythrocytes, at recombinant human P2Y2 and P2Y4 receptors, and at recombinant rat P2Y6 receptors. Similarly, compounds 2 and 3 did not have measurable affinity at adenosine A1, A2A, or A3 receptors. The lack of an aldehyde group in these derivatives indicates that Schiff's base formation with the P2X1 receptor is not necessarily required for recognition of pyridoxal phosphate derivatives. Thus, compounds 2 and 3 are relatively selective pharmacological probes of P2X1 receptors, filling a long-standing need in the P2 receptor field, and are also important lead compounds for future studies.
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PMID:A pyridoxine cyclic phosphate and its 6-azoaryl derivative selectively potentiate and antagonize activation of P2X1 receptors. 963 52

Microfluorometric measurements in Fura-2-loaded single cultured human vascular endothelial cells were used to characterize the intracellular calcium [Ca2+]i responses triggered by extracellular application of adenosine 5'-triphosphate (ATP) and other nucleotides. Application of ATP or uridine 5'-triphosphate (UTP) gave rise to dose-dependent elevations of [Ca2+]i in all the cells tested. At saturating concentrations of agonist, the [Ca2+]i response was biphasic, with an early peak and a sustained plateau. Unlike peak responses, the sustained Ca2+ plateau was sensitive to removal of Ca2+ from the external medium. Mn2+ quenching revealed the presence of Ca2+ influx during the agonist-induced calcium plateau. The agonist-evoked calcium plateau was inhibited in a dose-dependent manner by the Cl-channel blocker NPPB, by the divalent cation Ni2+ and by the imidazole antimycotic econazole. Previously, these compounds have been shown to block store-operated Ca2+ entry. The two phases of the agonist-evoked [Ca2+]i response were blocked by the specific phospholipase C inhibitor U-73122 and by intracellular injection of low molecular weight heparin, suggesting the involvement of IP3-sensitive intracellular Ca2+ stores. The pharmacological profile of the response, using different nucleotides and analogues, ATP = UTP > ADP = UDP, and no responses to P2X1 and P2Y1 agonists, suggested the involvement of P2Y2 receptors. The expression of mRNA for the P2Y2 receptor was detected by RT-PCR analysis. These results indicate that P2Y2 receptors linked to intracellular Ca2+ mobilization are present in human vascular endothelial cells. The initial [Ca2+]i mobilization is followed by a phase of elevated [Ca2+]i influx.
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PMID:Calcium signalling through nucleotide receptor P2Y2 in cultured human vascular endothelium. 980 12

Novel analogues of the P2 receptor antagonist pyridoxal-5'-phosphate 6-azophenyl-2',5'-disulfonate (2) were synthesized and studied as antagonists in functional assays at recombinant rat P2X1, P2X2, and P2X3 receptors expressed in Xenopus oocytes (ion flux stimulation) and at turkey erythrocyte P2Y1 receptors (phospholipase C activation). Selected compounds were also evaluated as antagonists of ion flux and the opening of a large pore at the recombinant human P2X7 receptor. Modifications were made in the 4-aldehyde and 5'-phosphate groups of the pyridoxal moiety: i.e. a CH2OH group at the 4-position in pyridoxine was either condensed as a cyclic phosphate or phosphorylated separately to form a bisphosphate, which reduced potency at P2 receptors. 5-Methylphosphonate substitution, anticipated to increase stability to hydrolysis, preserved P2 receptor potency. At the 6-position, halo, carboxylate, sulfonate, and phosphonate variations made on the phenylazo ring modulated potency at P2 receptors. The p-carboxyphenylazo analogue, 4, of phosphate 2 displayed an IC50 value of 9 nM at recombinant P2X1 receptors and was 1300-, 16-, and > 10,000-fold selective for P2X1 versus P2X2, P2X3, and P2Y1 subtypes, respectively. The corresponding 5-methylphosphonate was equipotent at P2X1 receptors. The 5-methylphosphonate analogue containing a 6-[3,5-bis(methylphosphonate)]phenylazo moiety, 9, had IC50 values of 11 and 25 nM at recombinant P2X1 and P2X3 receptors, respectively. The analogue containing a phenylazo 4-phosphonate group, 11, was also very potent at both P2X1 and P2X3 receptors. However, the corresponding 2,5-disulfonate analogue, 10, was 28-fold selective for P2X1 versus P2X3 receptors. None of the analogues were more potent at P2X7 and P2Y1 receptors than 2, which acted in the micromolar range at these two subtypes.
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PMID:Structure-activity relationships of pyridoxal phosphate derivatives as potent and selective antagonists of P2X1 receptors. 1146 75

This article summarizes the literature on receptor-operated Ca2(+)-permeable nonselective cation channels in vascular smooth muscle cells. One of these conductances, the P2X1 receptor, is a classic ligand-gated channel, but others are likely to be mediated via G-protein-coupled receptors. The most studied receptor-operated channel in vascular myocytes is the norepinephrine-evoked nonselective cation channel in rabbit portal vein myocytes. The data regarding the transduction mechanisms and biophysical properties of whole-cell and single-channel currents in this preparation are described. The channels have a conductance of 20 to 25 pS and complex kinetic behavior with at least two open and two closed states. These channels are activated by norepinephrine and acetylcholine via G-protein-coupled receptors linked to phospholipase C and by diacylglycerol (DAG). The action of DAG occurs by a mechanism independent of protein kinase C, but other kinases may mediate the responses to norepinephrine and DAG. In addition, activation of tyrosine kinases leads to opening of this channel. Other vasoconstrictors, such as endothelin, vasopressin, serotonin, and angiotensin II, open Ca2(+)-permeable nonselective cation channels, but there may be differences between these conductances and the norepinephrine-evoked channels. A homologue of the transient receptor potential protein (TRPC6) is an essential component of the norepinephrine-activated channel in rabbit portal vein, and it is likely that this family of proteins plays an important role in mediating Ca2+ influx in vascular smooth muscle.
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PMID:Receptor-operated Ca2(+)-permeable nonselective cation channels in vascular smooth muscle: a physiologic perspective. 1203 May 34

In the present study, we developed a novel method to analyze the calcium (Ca2+) signal in living slices of mouse caput epididymides by applying calcium imaging on Fura-2-loaded vibratome slices. The data revealed that in epithelial cells of mouse caput epididymides, ATP induces a rapid Ca2+ signal that is sustained after 60 sec. Preincubating the sections in Ca2+-free medium in the presence of EGTA did not affect the amplitude of the ATP-induced Ca2+ signal, indicating the presence of P2Y type purinergic receptors and phospholipase C activity. Furthermore, ATP induced a similar Ca2+ signal in the different subregions of caput epididymides. The P2X type ion-gated purinergic receptors could also be responsible for the ATP-induced Ca2+ signal because immunohistochemical and reverse transcriptase-polymerase chain reaction analyses showed that P2X1, P2X2, P2X4, P2X7, P2Y1, and P2Y2 receptors were expressed in the epididymis. We propose that P2X and P2Y receptor expression is vital for the normal function of epididymal epithelium and sperm maturation. Furthermore, the method we developed allows us to analyze the activity of various G protein-coupled receptors in intact epithelial cells of mouse epididymides, and other reproductive tissues as well.
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PMID:Adenosine triphosphate induces Ca2+ signal in epithelial cells of the mouse caput epididymis through activation of P2X and P2Y purinergic receptors. 1260 41

The effect of extracellular ATP (10-100 microM) on intracellular Ca2+ concentration ([Ca2+]i) and firing rate has been studied in single pacemaker cells isolated from the sinus venosus of cane toads. In spontaneously firing cells, ATP initially increased peak [Ca2+]i by 43 +/- 5 %, increased diastolic [Ca2+]i by 20 + 3 % and increased the firing rate by 58 +/- 8 %. These early effects were followed by a late phase in which both the peak [Ca2+]i and the firing rate declined. Adenosine, and UTP (respectively, P1- and P2Y2,4,6-selective agonists) caused no significant change in [Ca2+]i or firing rate, while alphabeta-methylene ATP (a P2X1,3 agonist) caused a small increase in firing rate but no changes in [Ca2+]i. In contrast the P2Y1-selective agonist 2-MesADP (1 microM) mimicked the biphasic effects of ATP and these effects were inhibited by the purinoceptor antagonists suramin and PPADS and by the P2Y1-selective antagonist MRS 2179. Immunohistochemistry established that P2Y1 purinoceptors were present on the cell surface. Western blotting analysis demonstrated that the P2Y1 antibody recognised a 57 kDa protein. After sarcoplasmic reticulum Ca2+ release was prevented with caffeine or ryanodine, ATP no longer had any effect on [Ca2+]i or firing rate. Furthermore, the SR Ca2+ store content was decreased during the late phase of 2-MesADP application. The effect of ATP was coupled to phospholipase C (PLC) activity because the PLC inhibitor U-73122 eliminated the effects of ATP. Our study shows that in toad pacemaker cells, the biphasic effects of ATP on pacemaker activity are mainly through P2Y1 purinoceptors, which are able to modulate Ca2+ release from the SR Ca2+ store.
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PMID:ATP modulates intracellular Ca2+ and firing rate through a P2Y1 purinoceptor in cane toad pacemaker cells. 1294 18

ATP receptors present on rat alveolar macrophages (NR8383 cells) were identified by recordings of membrane current, measurements of intracellular calcium, RT-PCR and immunocytochemistry. In whole-cell recordings with a sodium-based internal solution, ATP evoked an inward current at -60 mV. This reversed at 0 mV. The EC50 for ATP was 18 microM in normal external solution (calcium 2 mm, magnesium 1 mm). The currents evoked by 2',3-O-(4-benzoyl)benzoyl-ATP were about five-fold smaller than those observed with ATP. ADP, UTP and alphabeta-methylene-ATP (alphabetameATP) (up to 100 microM) had no effect. ATP-evoked currents were potentiated up to ten-fold by ivermectin and were unaffected by suramin (30-100 microM), pyridoxal-phosphate-6-azophenyl-(2,4-sulphonic acid) (30-100 microM), and brilliant blue G (1 microM). In whole-cell recordings with a potassium-based internal solution and low EGTA (0.01 mm), ATP evoked an inward current at -60 mV that was followed by larger outward current. ADP and UTP (1-100 microM) evoked only outward currents; these reversed polarity at the potassium equilibrium potential and were blocked by apamin (10 nm). Outward currents were also blocked by the phospholipase C inhibitor U73122 (1 microM), and they were not seen with higher intracellular EGTA (10 mm). Suramin (30 microM) blocked the outward currents evoked by ATP and UTP, but not that evoked by ADP. PPADS (10 microM) blocked the ADP-evoked outward current without altering the ATP or UTP currents. RT-PCR showed transcripts for P2X subunits 1, 4 and 7 (not 2, 3, 5, 6) and P2Y receptors 1, 2, 4 and 12 (not 6). Immunocytochemistry showed strong P2X4 receptor expression partly associated with the membrane, weak P2X7 staining that was not associated with the cell membrane, and no P2X1 receptor immunoreactivity. We conclude that rat alveolar macrophages express (probably homomeric) P2X4 receptors, but find no evidence for other functional P2X subtypes. The P2Y receptors are most likely P2Y1 and P2Y2 and these couple through phospholipase C to an increase in intracellular calcium and the opening of SK type potassium channels.
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PMID:P2X4, P2Y1 and P2Y2 receptors on rat alveolar macrophages. 1297 84


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