Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Quin 2-loaded isolated rabbit gastric glands and purified peptic cells were used to measure free cytosolic Ca2+ ([Ca2+]i) during hormone stimulation. Rabbit gastric glands are composed of peptic and parietal cells with less than 1% endocrine cells. Although both cell types responded to the same hormones, they may be distinguished in terms of the source of Ca2+ bringing about the change in [Ca2+]i. Experiments were designed to assign changes in [Ca2+]i to either the peptic or parietal cells and to attempt to maintain these distinctions in the mixed cell population of gastric glands. It was shown that the peptide cholecystokinin octapeptide induced a rapid and transient increase in [Ca2+]i of isolated peptic cells. This signal was independent of medium Ca2+ and insensitive to the Ca2+ channel blockers La3+ and nifedipine. In gastric glands, the Ca2+ outdependent increase in (Ca2+)i (the secondary transient) was slower and dose dependently blocked by La3+ and nifedipine. This allowed [Ca2+]i levels in the physiologically more intact rabbit gastric glands to be dissected and correlated with fluorescence changes of quin 2 in either cell type. The transient increase in [Ca2+]i coincided with a burst of pepsin but not acid secretion. A subsequent slower phase of pepsin secretion took place while the cells restored near resting [Ca2+]i. Using a combination of the Ca2+ ionophore A23187 and the protein kinase C activating phorbol ester 12-O-tetra-decanoylphorbol 13-acetate, the hormone response pattern of pepsin secretion could be mimicked. The intracellular Ca2+ stores of the peptic cells in the gastric gland remained depleted of Ca2+ until specific antagonists were added. The reloading of intracellular stores required medium Ca2+ although [Ca2+]i was maintained at resting level during the entire reloading period. Hence, a specialized pathway of Ca2+ reloading is postulated.
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PMID:Regulation of free cytosolic Ca2+ in the peptic and parietal cells of the rabbit gastric gland. 300 59

We have studied the onset of secretory responsiveness to cholecystokinin (CCK) during development of the rat exocrine pancreas. Although acinar cells of the fetal pancreas (1 d before birth) are filled with zymogen granules containing the secretory protein, alpha-amylase, the rate of amylase secretion from pancreatic lobules incubated in vitro was not increased in response to CCK. In contrast, the rate of CCK-stimulated amylase discharge from the neonatal pancreas (1 d after birth) was increased four- to eightfold above that of the fetal gland. The postnatal amplification of secretory responsiveness was not associated with an increase in the number or cell surface expression of 125I-CCK binding sites. When 125I-CCK-33 binding proteins were analyzed by affinity crosslinking, two proteins of Mr 210,000 and 100,000-160,000 were labeled specifically in both fetal and neonatal pancreas. To determine if cell surface receptors for CCK in the fetal pancreas are functional and able to generate a rise in the cytosolic [Ca++], we measured 45Ca++ efflux from tracer-loaded lobules. 45Ca++ efflux from both fetal and neonatal pancreas was comparably increased by CCK, indicating CCK-induced Ca++ mobilization and elevated cytosolic [Ca++]. The Ca++ ionophore A23187 also stimulated the rate of 45Ca++ extrusion from pancreas of both ages. Increased amylase secretion occurred concurrently with A23187-stimulated 45Ca++ efflux in neonatal pancreas, but not in the fetal gland. A23187 in combination with dibutyryl cAMP potentiated amylase release from the neonatal gland, but not from fetal pancreas. Similarly, the protein kinase C activator, phorbol dibutyrate, did not increase the rate of secretion from the fetal gland when added alone or in combination with A23187 or CCK. We suggest that CCK-receptor interaction in the fetal pancreas triggers intracellular Ca++ mobilization. However, one or more signal transduction events distal to Ca++ mobilization have not yet matured. The onset of secretory response to CCK that occurs postnatally may depend on amplification of these transduction events.
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PMID:Stimulus-secretion coupling in the developing exocrine pancreas: secretory responsiveness to cholecystokinin. 302 99

Many hormones and neurotransmitters exert their biological effects by increasing the levels of Ca2+ and 1,2-diacylglycerol in their target cells. Major agonists that act in this way are epinephrine and norepinephrine, acetylcholine, vasopressin, cholecystokinin, and angiotensin II. These and other Ca2+-mobilizing agonists may also produce effects that are not mediated by Ca2+ or diacylglycerol, but involve separate receptors and an increase or decrease in cyclic AMP. The general mechanisms by which Ca2+-mobilizing agonists induce their physiological responses are depicted in Fig. 12. These responses appear to involve an initial mobilization of Ca2+ from endoplasmic reticulum and perhaps other intracellular Ca2+ stores, followed by alterations in the flux of Ca2+ across the plasma membrane. The Ca2+ changes are consistently associated with increased turnover of cellular phosphoinositides. The most rapid response is breakdown of phosphatidylinositol 4,5-P2 in the plasma membrane, and there is much evidence that this involves a guanine-nucleotide-binding regulatory protein similar to those involved in the regulation of adenylate cyclase. Myo-inositol 1,4,5-P3 produced by phosphatidylinositol 4,5-P2 breakdown rapidly releases Ca2+ from endoplasmic reticulum, and it is likely that it is the long-sought second message for the Ca2+-dependent hormones. 1,2-Diacylglycerol, the other product of phosphatidylinositol 4,5-P2 breakdown, also acts as a second message in that it activates protein kinase C, a Ca2+-phospholipid-dependent protein kinase, by lowering its requirement for Ca2+. The cellular substrates for protein kinase C and its role in the different physiological responses to the Ca2+-mediated agonists are currently being defined. The major intracellular target for Ca2+ is the Ca2+-dependent regulatory protein calmodulin. This binds Ca2+ with high affinity, and the resulting complex interacts with a variety of enzymes and other cellular proteins, modifying their activities. A major target is the multifunctional calmodulin-dependent protein kinase that phosphorylates and alters the activities of many proteins, for example, glycogen synthase and tyrosine hydroxylase. Calcium ions may also stimulate calmodulin-dependent protein kinases that are more specific, such as phosphorylase kinase and myosin light-chain kinase. Other important Ca2+-calmodulin targets are the microtubule-associated proteins, but it is likely that many more will be found.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mechanisms involved in calcium-mobilizing agonist responses. 302 85

We have examined the effect of carbamylcholine on the binding of cholecystokinin (CCK) to dispersed acini from rat pancreas. The CCK receptor on pancreatic acini possesses two classes of binding sites. Simultaneous addition of carbamylcholine inhibited binding of CCK to acini due to an apparent loss of high affinity CCK binding sites. Atropine prevented the inhibitory effect of carbamylcholine, whereas calcium ionophore A23187 did not alter binding of CCK. 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibited binding of CCK in the same manner as carbamylcholine. Inhibition by carbamylcholine was reversible and the recovery was time dependent. By contrast, inhibition of binding of CCK by TPA did not reverse after a 60-min incubation without the agent. These findings, at least in part, account for the inhibition of the CCK-induced stimulation of amylase secretion by carbamylcholine. The action of TPA on binding of CCK suggests the possible involvement of the activation of protein kinase C in the inhibition of binding.
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PMID:Carbachol regulates cholecystokinin receptor on pancreatic acinar cells. 310 10

D,L-Palmitoyl carnitine (PC), an inhibitor of protein kinase C, decreased [125I]epidermal growth factor (EGF) cell-associated radioactivity in rat pancreatic acini. H-7, another inhibitor of protein kinase C, failed to inhibit [125I]EGF binding. Palmitate, carnitine, acetylcarnitine, and 2-tetradecylglycidic acid methyl ester (a specific inhibitor of endogenous PC formation) did not alter [125I]EGF binding. PC conjugated to bovine serum albumin (PC-BSA) decreased [125I]EGF cell-associated radioactivity to the same extent as PC. Neither compound affected the distribution of cell-associated radioactivity into acid-resistant and acid-dissociable compartments. In contrast, cholecystokinin octapeptide (CCK8) and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) markedly inhibited the distribution of [125I]EGF into the acid-resistant compartment. Proglumide, a competitive antagonist of CCK8, reversed the inhibitory action of CCK8 but not that of PC-BSA. PC-BSA did not inhibit [125I]insulin binding, and did not enhance amylase release, a Ca2+-mediated effect. Further, its inhibitory effect on [125I]EGF cell-associated radioactivity was not additive with the inhibitory effect of the calcium ionophore A23187. Both PC-BSA and H-7 inhibited Ca2+- and phospholipid-dependent kinase activity in soluble and particulate fractions when added to disrupted acini, but in the particulate compartment only when added to intact acini. These findings suggest that PC-BSA may regulate EGF binding via a novel mechanism that is independent of protein kinase C activation or Ca2+ mobilization.
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PMID:Inhibition of epidermal growth factor binding in rat pancreatic acini by palmitoyl carnitine: evidence for Ca2+ and protein kinase C independent regulation. 310 49

Cholecystokinin-octapeptide (CCK8) inhibits 125I-labeled epidermal growth factor (EGF) cell-associated radioactivity in pancreatic acini, ostensibly as a result of its ability to mobilize cellular Ca2+. The phorbol ester tetradecanoyl phorbol acetate (TPA), a compound that activates protein kinase C, mimics the inhibitory action of CCK8. In the present study we examined the relationship between occupancy of the cholecystokinin (CCK) receptor, the subsequent inhibition of EGF binding, and the potential role of C-kinase activation in mediating this inhibition. Proglumide and dibutyryl cyclic GMP (dbGMP), two distinct competitive antagonists of CCK8, reversed the inhibitory actions of CCK8. Analysis of steady-state saturation kinetics of 125I-EGF binding indicated that CCK8 decreased the apparent affinity of the EGF receptor, mainly as a result of a marked decrease in the amount of internalized ligand. TPA also inhibited 125I-EGF internalization. Removal of CCK8 and TPA from incubation medium did not abolish their inhibitory actions. Carbachol, but not bombesin, exerted a similar residual inhibitory effect. It is suggested that in addition to acting via Ca2+, certain pancreatic secretagogues may also act through C-kinase to regulate EGF binding.
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PMID:Residual inhibition of epidermal growth factor binding by pancreatic secretagogues and phorbol ester in rat pancreas. 387 45

The association of 125I-labelled epidermal growth factor (125I-EGF) with mouse pancreatic acinar cells was inhibited by secretagogues which increase intracellular free Ca2+ concentrations. These agents included cholecystokinin-octapeptide (CCK8) and the Ca2+ ionophore A23187. Inhibition by CCK8 was blocked by lowering the incubation temperature from 37 degrees C to 15 degrees C. Moreover, in contrast with studies of intact acini, the binding of 125I-EGF to isolated acinar membrane particles was not affected either by CCK8, or by varying the level of Ca2+ in the incubation medium. These results indicated, therefore, that the inhibition of 125I-EGF association with acinar cells required intact cells that are metabolically active. Since intact cells at 37 degrees C are known to internalize bound EGF rapidly, acid washing was used to distinguish membrane-associated hormone from internalized hormone. Under steady-state conditions 86% of the 125I-EGF associated with the acini was found to be internalized by this technique. When agents that increased intracellular Ca2+ were tested they all markedly reduced the amount of internalized hormone, whereas surface binding was only minimally affected. The phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA), which is known to activate protein kinase C, a Ca2+-regulated enzyme, also inhibited the association of EGF with acini. This inhibition was similar to that induced by elevated intracellular Ca2+. To test whether these two inhibitory phenomena were related, the effects of TPA in combination with the Ca2+ ionophore A23187 were examined. At low concentrations the effects were synergistic, whereas at high concentrations the maximal level of inhibition was not changed. We suggest therefore that elevated intracellular Ca2+ and phorbol esters may inhibit EGF internalization by a mechanism involving activation of protein kinase C.
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PMID:Intracellular Ca2+ and phorbol esters synergistically inhibit internalization of epidermal growth factor in pancreatic acini. 609 11

We previously demonstrated that the supramaximally effective concentrations of caerulein caused marked changes in the apical cytoskeleton of the rat pancreatic acinar cell. These changes included ablation of microvilli, the terminal actin web, and intermediate filament bands. The present study was designed to elucidate part of the intracellular signalling mechanism mediating these changes. For these studies we used a cholecystokinin (CCK) analogue, CCK-JMV-180, that has been previously demonstrated not to inhibit enzyme secretion and to prevent the inhibition caused by caerulein. We investigated the effects of CCK-JMV-180 alone and in combination with supramaximal concentrations of caerulein on the morphology of the apical structures, on 1,2-diacylglycerol production (a measure of phospholipase C activity), and on amylase secretion in rat pancreatic acini. Supramaximally effective concentrations of caerulein caused inhibition of enzyme secretion. CCK-JMV-180 had no effect on the ultrastructure of the apical region of the acinar cell and it prevented the ablation of apical cytoskeleton induced by a supramaximal concentration of caerulein (10 nM). CCK-JMV-180 inhibited the increase in 1,2-diacylglycerol formation and the inhibition of amylase release caused by 10 nM caerulein. Mimicking the effect of 1,2-diacylglycerol on activation of protein kinase C with phorbol 12-myristate 13-acetate and reproducing changes in [Ca2+]i caused by 10 nM caerulein with 100 nM bombesin did not alter the apical cytoskeleton. These results suggest that the cytoskeletal changes observed with inhibitory concentrations of caerulein are caused by the phospholipase C effects of caerulein on membrane phospholipids.
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PMID:Cholecystokinin JMV-180 and caerulein effects on the pancreatic acinar cell cytoskeleton. 750 12

The present study examined whether NO synthase (NOS) activity in gastric muscle cells was inhibited by protein kinase C (PKC). Vasoactive intestinal peptide (VIP) increased L-[3H]citrulline production (a coproduct and index of NO synthesis) in muscle strips (81.9 +/- 11.6%) and dispersed muscle cells (80.9 +/- 4.6%) of rabbit stomach. Cholecystokinin octapeptide (CCK-8), carbachol, and phorbol 12-myristate 13-acetate (PMA) inhibited VIP-induced L-[3H]citrulline production in muscle cells and muscle strips; the inhibition was reversed by pretreatment with the PKC inhibitor, calphostin C. The Ca(2+)-mobilizing agents, CCK-8, acetylcholine, ionomycin, and KCl, all of which increased PKC activity in dispersed muscle cells, did not increase L-[3H]citrulline production. After treatment of the cells with calphostin C, all four agents stimulated L-[3H]citrulline production, although to a lesser extent than VIP (approximately 50%). VIP-induced relaxation of basal but not carbachol-stimulated tension was accompanied by increase in L-[3H]citrulline production and was inhibited by the NOS inhibitor NG-nitro-L-arginine (L-NNA). Preincubation of carbachol-treated muscle strips with calphostin C restored the ability of VIP to stimulate L-[3H]citrulline production and the ability of L-NNA to inhibit VIP-induced relaxation. We conclude that 1) VIP-stimulated NOS activity is inhibited by agents that increase PKC activity in gastric smooth muscle cells, and 2) agents that increase both cytosolic free Ca2+ concentration and PKC activity stimulate NOS activity only when PKC activity is suppressed.
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PMID:Inhibition of nitric oxide synthase activity in dispersed gastric muscle cells by protein kinase C. 750 98

The oscillations in cytosolic Ca2+ evoked in pancreatic exocrine acinar cells by submaximal concentrations of the two phosphoinositidase-coupled agonists acetylcholine (ACh) and cholecystokinin octapeptide (CCK-8) have very different temporal patterns. In the present study we use digital video imaging of Fura-2 fluorescence to map the spatial distribution of Ca2+ during the oscillating responses to these two agonists. The spatial patterns induced are very different for each of these agonists. ACh oscillations are sinusoidal and initiated at the secretory pole of these morphologically and functionally polarized cells. As they spread across the cell, pronounced gradients in Ca2+ develop that persist throughout the oscillating response. CCK-8 induces a series of discrete Ca2+ transients of longer duration and lower frequency. These elevations in Ca2+ arise slowly, throughout the cells and without any detectable gradients in Ca2+. We consider that the different spatiotemporal patterns can be explained on the basis of a physiologically relevant interaction between Ins(1,4,5)P3 and protein kinase C in second messenger-mediated Ca2+ signalling.
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PMID:Two different spatiotemporal patterns for Ca2+ oscillations in pancreatic acinar cells: evidence of a role for protein kinase C in Ins(1,4,5)P3-mediated Ca2+ signalling. 751 May 80


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