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)

The incubation of isolated rat pancreatic acini with low doses (1 x 10(-11)-1 x 10(-10) M) of cholecystokinin-octapeptide (CCK8) induced amylase release. This CCK8-induced amylase release has been shown to be mediated through the protein kinase C activation and the Ca2+ mobilization which are linked to the phospholipase C-mediated hydrolysis of phosphoinositides. However, the incubation of the acini with high doses (1 x 10(-9)-1 x 10(-7) M) of CCK8 reduced amylase release to the level less than that induced by the maximally effective dose (1 x 10(-10) M) of this secretagogue. Under the same conditions, the high doses of this secretagogue did not inhibit the phospholipase C-mediated hydrolysis of phosphoinositides. The stimulatory action of the maximally effective dose of CCK8 in amylase release was mimicked by the simultaneous addition of protein kinase C-activating 12-O-tetradecanoylphorbol-13-acetate (TPA) and Ca2+ ionophore A23187. A high dose (1 x 10(-7) M) of CCK8 reduced the amylase release induced by the combination of TPA and A23187. These results suggest that the high doses of CCK8 inhibit the secretory process post to the protein kinase C-Ca2+ systems and thereby reduce the amylase release induced by the maximally effective dose of CCK8 in rat pancreatic acini.
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PMID:Mode of inhibitory action of cholecystokinin in amylase release from isolated rat pancreatic acini--inhibition of secretory process post to protein kinase C-calcium ion systems. 245 69

Changes in the cellular content of 1,2-diacylglycerol (DAG) in isolated rat pancreatic acini in response to agonist stimulation were studied using a sensitive mass assay. When acini were stimulated by 10 nM COOH-terminal cholecystokinin-octapeptide (CCK8), the increase in DAG was biphasic, consisting of an early peak at 5 s and a second, larger, gradual increase that was maximal by 15 min. The basal level of DAG in acini was 1.04 nmol/mg of protein, which was increased to 1.24 nmol/mg of protein at 5 s and 2.76 nmol/mg of protein at 30 min. In comparison, the increase in DAG stimulated by 30 pM CCK8, a submaximal concentration for amylase release, was monophasic, increasing without an early peak but sustained to 60 min. Other Ca2+-mobilizing secretagogues such as carbamylcholine and bombesin increased DAG in acini, whereas vasoactive intestinal peptide, which acts to increase cAMP, had no effect. Phorbol ester and Ca2+ ionophore also stimulated DAG production. Analysis of the mass level of inositol 1,4,5-trisphosphate (1,4,5-IP3) showed that the generation of 1,4,5-IP3 stimulated by 10 nM CCK8 peaked at 5 s, a finding consistent with the early peak of DAG. The basal level was 4.7 pmol/mg of protein, which was increased to 144.6 pmol/mg of protein at 5 s by 10 nM CCK8. The levels of 1,4,5-IP3 then returned toward basal in contrast to the gradual and sustained increase of DAG. The dose dependencies of 1,4,5-IP3 and DAG formation at 5 s with respect to CCK8 were almost identical. This suggests that phosphatidylinositol 4,5-bisphosphate hydrolysis is a major source of the early increase in DAG but not of the sustained increase in DAG. Therefore, a possible contribution of phosphatidylcholine hydrolysis to DAG formation was examined utilizing acini prelabeled with [3H]choline. CCK8 (1 nM) maximally increased [3H]choline metabolite release by 133% of control at 30 min. Separation of these metabolites by thin layer chromatography showed that the products of CCK8-stimulated release were almost entirely phosphorylcholine, indicating the activation of a phospholipase C specific for phosphatidylcholine. By comparison, 1 nM CCK8 stimulated [3H]ethanolamine metabolite release from [3H]ethanolamine-labeled acini by only 22% of control. These data suggest that CCK stimulates both phosphatidylinositol 4,5-bisphosphate and phosphatidylcholine hydrolysis; the latter may contribute to the sustained generation of DAG and hence the maintained activation of protein kinase C.
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PMID:Multiple sources of 1,2-diacylglycerol in isolated rat pancreatic acini stimulated by cholecystokinin. Involvement of phosphatidylinositol bisphosphate and phosphatidylcholine hydrolysis. 254 32

The dipeptoid cholecystokinin (CCK)B antagonists PD136450, Cam-1279 and CI988 stimulated amylase release from isolated rat pancreatic acini with an efficacy similar to CCK8, but with a much weaker potency (ED50, 0.6, 0.9 and 1.3 microM, respectively). In contrast to CCK8, however, none of these compounds elicited inhibition of amylase release at supramaximal concentrations. In addition, 10(-4) M PD136450 blocked the inhibition induced by high concentrations of CCK8. Competitive inhibition of [125I]BH-CCK8 binding by PD136450 indicated that this compound bound with a single affinity state to all CCK receptors on acini. Maximal stimulation of amylase release by PD136450 was dependent upon occupation of virtually the entire complement of CCK receptors. PD136450 at all concentrations examined had only a limited ability to stimulate total phosphoinositide hydrolysis and at maximum induced only 20% of maximal CCK stimulation. Measurement of intracellular calcium ([Ca++]i) by digital imaging of Fura-2 indicated that 1 microM PD136450 induced repetitive [Ca++]i oscillations with a magnitude of 346.0 +/- 4.5 nM and frequency of 1.3 cycles per min. These oscillations were still present in Ca(++)-free medium and were blocked by the phospholipase C inhibitor, U73122. Because the dipeptoid compounds can occupy all available pancreatic CCKA receptors, these compounds must induce a configuration of the receptor different from either CCK8 or the previously characterized partial agonist CCK-JMV-180, thereby inducing a distinct signaling pattern. Because the dipeptoid compounds do not fully mimic CCK actions, it is likely that they interact with only some of the critical binding sites within the CCKA receptor normally occupied by CCK8.
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PMID:Characterization of cholecystokininA receptor agonist activity by a family of cholecystokininB receptor antagonists. 751 69

Epidermal growth factor (EGF) regulates pancreatic acinar enzyme secretion. The mechanism of action of EGF in pancreatic acinar cells is not clear. In the present study we investigated the role of heterotrimeric GTP-binding proteins (G proteins) in EGF receptor signal transduction. Pancreatic acini were isolated from rat pancreas by collagenase digestion and permeabilized by digitonin. Activation of phosphatidylinositol 4,5-bisphosphate-specific phospholipase C (PLC) was assessed using a radioreceptor assay specific for inositol 1,4,5-trisphosphate [IP3(1,4,5)]. For measurement of amylase secretion isolated pancreatic acini were incubated with secretagogues for 30 min at 37 degrees C. Amylase released into the medium was assessed by monitoring the hydrolysis rate of p-nitrophenyl-alpha,D-maltohepatoside. The weakly hydrolyzable GTP analogue guanosine 5'-[3-O-thio]triphosphate (GTP gamma S) and guanosine 5'-diphosphate (GDP) were used to activate and inhibit G protein-mediated signal transduction, respectively. EGF (90 nM) stimulated amylase release in isolated pancreatic acini. This effect was enhanced by guanosine 5'-[3-O-thio]triphosphate (0.1 mM), which stimulates G proteins. Guanosine 5'-diphosphate (1 mM), which inhibits the activity of heterotrimeric G proteins, had no effect on basal and EGF-induced amylase release. Lower EGF concentrations (20 nM) inhibited COOH-terminal cholecystokinin octapeptide (CCK8)-induced IP3(1,4,5) production and amylase release in pancreatic acini). However, in the presence of GDP, EGF had no significant effect on CCK8-stimulated amylase release. Furthermore, coincubation of the acini with CCK8, EGF, and GDP revealed that GDP reduces the inhibitory effect of EGF on CCK8-induced IP3(1,4,5) production.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Epidermal growth factor receptor signaling in rat pancreatic acinar cells. 754 69

In this study we report that a synthetic peptide of the effector domain of rab3A (rab3AL(33-48)) stimulates both amylase secretion and inositol 1,4,5-trisphosphate (IP3)-accumulation in digitonin-permeabilized pancreatic acini in an analogous way to cholecystokinin-octapeptide (CCK8). Maximum CCK8-induced IP3-accumulation was observed at five seconds after addition of CCK8 to the acini. Maximum rab3AL(33-48)-induced IP3-production occurred 15 to 30 seconds after addition of rab3AL(33-48); then the acinar IP3 content declined towards the basal level. Heparin, an inhibitor of IP3 binding to its receptor, inhibited both rab3AL(33-48)- and CCK8-stimulated amylase secretion without affecting the response to vasoactive intestinal polypeptide. rab3AL(33-48) had no effect in intact acini, indicating that the site of action of rab3AL(33-48) is intracellular. We conclude that rab-like small molecular weight GTP-binding proteins regulate phospholipase C activity and thereby amylase secretion from inside of the cell.
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PMID:A synthetic peptide of the effector domain of rab3A stimulates inositol 1,4,5-trisphosphate production in digitonin-permeabilized pancreatic acini. 768 59

Imaging [Ca2+]i at high temporal resolution and measuring the properties of Ca2+ signaling in streptolysin O (SLO)-permeabilized cells were used to study the spacial organization of signaling complexes. Sequential stimulation of single cells within pancreatic acini with several Ca2+-mobilizing agonists revealed an agonist-specific pattern and propagation rate of Ca2+ waves in the same cells, with CCK8 stimulating the fastest and bombesin the slowest waves. More importantly, each agonist initiated the wave in a different region of the same cell. On the other hand, repetitive stimulation with the same agonist induced Ca2+ waves of the same pattern that were initiated from the same region of the cell. The agonist-specific Ca2+ signaling does not appear to be the result of coupling to different G proteins as infusion of an anti-Galphaq antibody into the cells through a patch pipette equally inhibited Ca2+ signaling by all agonists. Further evidence for compartmentalization of signaling complexes was developed in permeabilized cells. The time-dependent loss of Ca2+ signaling due to SLO permeabilization occurred in an agonist-specific manner in the sequence cabachol > bombesin > cholecystokinin. Signaling by all agonists could be completely restored with as low as 2 micro guanosine 5'-3-O-(thio)triphosphate (GTPgammaS). At this low concentration GTPgammaS recoupled inositol 1,4,5-trisphosphate production and Ca2+ release, rather than enhancing phospholipase C activity. Priming of Ca2+ signaling by GTPgammaS was agonist-specific. Guanosine 5'-O-(thio)diphosphate (GDPbetaS) uncoupled the ability of signaling complexes to release Ca2+ much better than stimulating inositol 1,4,5-trisphosphate production. The uncoupling of Ca2+ signaling by GDPbetaS was also agonist-specific. The combined findings of agonist-specific initiation sites of the Ca2+ wave and differential access of guanine nucleotides to signaling complexes suggest spacial compartmentalization of Ca2+ signaling complexes. Each complex must include a receptor, G protein, and phospholipase C that are coupled to a specific portion of the Ca2+ pool.
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PMID:Spacial compartmentalization of Ca2+ signaling complexes in pancreatic acini. 879 36

At present little is known about how the low-affinity cholecystokinin receptor inhibits secretagogue-stimulated amylase secretion from pancreatic acinar cells. To examine this question we have determined how cholecystokinin octapeptide (CCK8) influences Ca2+-dependent amylase secretion from alpha-toxin-permeabilized pancreatic acini. CCK8 significantly inhibited Ca2+-stimulated amylase secretion. The inhibitory actions of CCK8 were completely blocked by the addition of JMV-180, a specific antagonist for the low-affinity CCK8 receptor. Previous studies have shown that Ca2+-dependent amylase secretion from alpha-toxin-permeabilized acini has two distinct phases [Padfield and Panesar (1997) Am. J. Physiol. 36, G655-660]. There is an initial rapid phase of secretion which represents release from exocytotic sites primed by MgATP prior to permeabilization. This is followed by a slower sustained phase of secretion which, in part, reflects the MgATP-dependent repriming of the exocytotic machinery. CCK8 did not influence the initial rapid phase of the Ca2+-dependent secretory response, but inhibited the second slower sustained phase. Moreover, CCK8 was shown to inhibit the MgATP-dependent priming of exocytosis in the acini. These results indicate that the low-affinity CCK receptor blocks stimulated amylase secretion by inhibiting the MgATP-dependent repriming of exocytosis.
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PMID:Cholecystokinin octapeptide inhibits Ca2+-dependent amylase secretion from permeabilized pancreatic acini by blocking the MgATP-dependent priming of exocytosis. 946 27

In addition to its fundamental role in stimulating gastric acid secretion, the peptide hormone gastrin induces growth-promoting effects on diversity of target cells. Various mechanisms, including endocrine, paracrine, and autocrine, have been proposed for gastrin's growth-promoting actions. The mitogenic effects of gastrin are mediated by specific cell surface receptors activated after gastrin binding. The functionally defined receptors for gastrin include cholecystokinin A (CCKA) receptor, which is discriminating for sulfated CCK8; cholecystokinin B (CCKB)/gastrin receptor, which binds gastrin17 sulfated, and nonsulfated CCK8 with nearly equal affinities; cholecystokinin C (CCKC), which is a low-affinity gastrin binding protein; and novel, high-affinity receptors selective for amidated gastrin, processing intermediates of gastrin, or both. The signaling pathways mediating gastrin's stimulation of the CCKB/gastrin receptor have been progressively outlined, and the pathways mediating other receptors have been slowly emerging. Engagement of the gastrin receptor initiates various biochemical and molecular events, including recruitment and activation of tyrosine kinases, activation of the phospholipase C signaling pathway leading to phosphoinositide breakdown, intracellular calcium mobilization and protein kinase C stimulation, activation of the mitogen-activated protein kinase pathway, and induction of early response genes. Current emphasis is on understanding the functional significance of processing intermediate forms of gastrin, and the receptor subtypes and pathways that promote the trophic/mitogenic effects of the different molecular forms of gastrin.
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PMID:Signaling pathways mediating gastrin's growth-promoting effects. 1047 91