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)

Phenylephrine is known to stimulate translocation of protein kinase C in rat pinealocytes (Sugden, D., Vanecek, J., Klein, D.C., Thomas, T.P., and Anderson, W. B. (1985) Nature 314, 359-361). In the present study, the receptor mediating this effect was found to belong to the alpha 1-adrenoceptor subclass. Activation of this receptor is also known to produce a sustained increase in [Ca2+]i by increasing net influx (Sugden, A. L., Sugden, D., and Klein, D. C. (1985) J. Biol. Chem. 261, 11608-11612), which points to the possible importance of Ca2+ influx in the subcellular redistribution (activation) of protein kinase C in intact cells. This possibility was investigated by reducing extracellular Ca2+ ((Ca2+]o) with EGTA or by inhibiting Ca2+ influx with inorganic Ca2+ blockers. These treatments reduced alpha 1-adrenoceptor-mediated translocation of protein kinase C. This suggested that elevation of Ca2+ influx alone triggers activation of protein kinase C. In support of this, it was found that treatments which elevate Ca2+ influx, including increased extracellular K+ and addition of the Ca2+ ionophore A23187, cause redistribution of protein kinase C. The effect of K+ was blocked by nifedipine and that of A23187 by EGTA, indicating that effects of these agents are Ca2+-dependent. The possible role of phospholipase C activation in these effects was examined by measuring the formation of [3H]diacylglycerol by cells labeled with [3H]arachidonic acid. Although [3H]diacylglycerol formation was easily detected in the presence or absence of an effective concentration of an inhibitor of diacylglycerol kinase, none of the agents which cause rapid translocation of protein kinase C were found to cause a rapid increase in the generation of [3H]diacylglycerol. These findings establish that an increase in Ca2+ influx is sufficient to trigger translocation of protein kinase C. In addition, we found that a very close correlation exists between translocation of protein kinase C by phenylephrine, K+, and A23187 and their ability to potentiate beta-adrenergic stimulation of cAMP and cGMP accumulation. This provides strong support to the proposal that translocation of protein kinase C is required for potentiation of beta-adrenergic stimulation of pinealocyte cAMP and cGMP accumulation.
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PMID:Protein kinase C: subcellular redistribution by increased Ca2+ influx. Evidence that Ca2+-dependent subcellular redistribution of protein kinase C is involved in potentiation of beta-adrenergic stimulation of pineal cAMP and cGMP by K+ and A23187. 289 66

We previously suggested that insulin increases diacylglycerol (DAG) in BC3H-1 myocytes, both by increases in synthesis de novo of phosphatidic acid (PA) and by hydrolysis of non-inositol-containing phospholipids, such as phosphatidylcholine (PC) and phosphatidylethanolamine (PE). We have now evaluated these insulin effects more thoroughly, and several potential mechanisms for their induction. In studies of the effect on PA synthesis de novo, insulin stimulated [2-3H]glycerol incorporation into PA, DAG, PC/PE and total glycerolipids of BC3H-1 myocytes, regardless of whether insulin was added simultaneously with, or after 2 h or 3 or 10 days of prelabelling with, [2-3H]glycerol. In prelabelled cells, time-related changes in [2-3H]glycerol labelling of DAG correlated well with increases in DAG content: both were maximal in 30-60 s and persisted for 20-30 min. [2-3H]Glycerol labelling of glycerol 3-phosphate, on the other hand, was decreased by insulin, presumably reflecting increased utilization for PA synthesis. Glycerol 3-phosphate concentrations were 0.36 and 0.38 mM before and 1 min after insulin treatment, and insulin effects could not be explained by increases in glycerol 3-phosphate specific radioactivity. In addition to that of [2-3H]glycerol, insulin increased [U-14C]glucose and [1,2,3-3H]glycerol incorporation into DAG and other glycerolipids. Effects of insulin on [2-3H]glycerol incorporation into DAG and other glycerolipids were half-maximal and maximal at 2 nM- and 20 nM-insulin respectively, and were not dependent on glucose concentration in the medium, extracellular Ca2+ or protein synthesis. Despite good correlation between [3H]DAG and DAG content, calculated increases in DAG content from glycerol 3-phosphate specific radioactivity (i.e. via the pathway of PA synthesis de novo) could account for only 15-30% of the observed increases in DAG content. In addition to increases in [3H]glycerol labelling of PC/PE, insulin rapidly (within 30 s) increased PC/PE labelling by [3H]arachidonic acid, [3H]myristic acid, and [14C]choline. Phenylephrine, ionophore A23187 and phorbol esters did not increase [2-3H]glycerol incorporation into DAG or other glycerolipids in 2-h-prelabelling experiments; thus activation of the phospholipase C which hydrolyses phosphatidylinositol, its mono- and bis-phosphate, Ca2+ mobilization, and protein kinase C activation, appear to be ruled out as mechanisms to explain the insulin effect on synthesis de novo of PA, DAG and PC.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mechanisms whereby insulin increases diacylglycerol in BC3H-1 myocytes. 314 71

We have previously suggested that insulin effects on 2-deoxyglucose (2-DOG) uptake in BC3H-1 myocytes are due to increases in de novo phospholipid synthesis, diacylglycerol generation, and protein kinase C activation. To test this hypothesis further, we examined the effects of phenylephrine, an agonist that increases diacylglycerol and protein kinase C activity through phospholipase C activation. As evidence for phospholipase activation in BC3H-1 myocytes, we found that phenylephrine increased acute 32PO4 incorporation into phosphatidic acid and phosphatidylinositol, generation of [3H]inositol phosphates from prelabeled [3H]inositol phospholipids, cytosolic Ca2+, and membrane-bound protein kinase C. Phenylephrine also provoked dose-related increases in [3H]2-DOG uptake that were similar in magnitude and time course to those induced by insulin. As with insulin, phenylephrine effects on 2-DOG uptake were not apparent in myocytes that were maximally stimulated with 12-O-tetradecanoylphorbol-13-acetate, a diacylglycerol analogue that activates protein kinase C. These findings support our hypothesis that diacylglycerol generation and protein kinase C activation may be important in the stimulation of glucose uptake by agents such as phenylephrine and insulin that activate the phosphoinositide cycle.
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PMID:Further evidence implicating diacylglycerol generation and protein kinase C activation in agonist-induced increases in glucose uptake. Insulin-like effects of phenylephrine in BC3H-1 myocytes. 352 26

Because previous studies have suggested that ocular effects of adrenergic agonists are in part attributable to arachidonate metabolites, the effect of phenylephrine on synthesis and release of arachidonic acid (AA) and prostaglandins from isolated rabbit iris-ciliary body (ICB) slices was examined. ICB concentrated and incorporated exogenous 14C-AA into tissue phospholipid and neutral lipid stores. During the period of 14C-AA labeling of tissue lipids, a portion of AA was converted to prostaglandins (PGs), as determined by thin-layer chromatography in two solvent systems and by prevention of PG synthesis by indomethacin. PGs E2 and F2 alpha were the major PGs synthesized. PGD2, thromboxane B2, and 6-keto-PGF 1 alpha were also synthesized by ICB. Phenylephrine enhanced PGE2 and PGF2 alpha synthesis and release from superfused 14C-AA-labeled ICB. PGE2 was the major PG released upon stimulation by phenylephrine. Phenoxybenzamine, an alpha-adrenergic receptor antagonists, and indomethacin prevented phenylephrine-induced PG release. The phenylephrine-induced PG release thus represented newly synthesized PG and was a result of the alpha-adrenergic activity of phenylephrine. Phenoxybenzamine treatment did not inhibit enzymes involved in PG synthesis, inasmuch as bradykinin was capable of markedly stimulating PG release from IBC treated with phenoxybenzamine. Esterification of 14C-AA into a lipid tentatively identified as 1,2-diacylglycerol was also demonstrated. The presence of this glyceride suggests that ICB exhibits phosphatidylinositol turnover and that phospholipase C and diacylglycerol lipase activities might be involved in supplying AA for ocular PG synthesis upon alpha-adrenergic stimulation.
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PMID:Alpha-adrenergic stimulation of prostaglandin release from rabbit iris-ciliary body in vitro. 612 64

This study explored whether Staphylococcus aureus alpha-toxin can permeabilize the ventricular muscle and whether the treatment can leave cardiac membrane receptors, intracellular Ca2+ stores and the Ca2+ sensitivity of myofilament without damage. After alpha-toxin treatment, the trabeculae from guinea-pig ventricles developed tension at very low Ca2+ concentration ([Ca2+]) (approximately 0.6 microM) in high K+ solution. The trabeculae could contract transiently with 20 mM caffeine after incubating the muscle in a solution containing 0.5 microM [Ca2+]. Phenylephrine (20 microM) with or without GTP gamma S, a non-hydrolyzable analogue of GTP, in the incubating solution did not change the caffeine-induced tension transient. After loading intracellular Ca2+ stores with Ca2+, Ca2+ could be released from the stores by the [Ca2+] of 1.6 microM since the caffeine-induced tension transient was smaller than without Ca2+ releasing protocol. Phenylephrine with or without 100 microM GTP in the releasing solution did not modify the caffeine-induced tension transient. When the muscle was bathed in 1.6 microM Ca2+ solution containing 5 mM EGTA, the developed tension was maintained stably for more than 2 h. Phenylephrine with or without GTP, GTP alone, or 20 microM inositol 1,4,5-trisphosphate (InsP3) did not change the maintained tension. The amplitude and the rate of spontaneous contractions, induced at the free [Ca2+] around 0.5 microM, were not modified by phenylephrine, with or without GTP, and InsP3. These results show that alpha-toxin is useful at least to permeabilize the cardiac muscle to ions and small molecules without damaging the internal membrane and contractile machinery.
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PMID:Contractility of alpha-toxin permeabilized ventricular muscle of guinea pig. 789 6

The effects of aclarubicin on phosphatidylinositol hydrolysis and contractile responses were investigated in isolated rat aorta. In the aclarubicin-pretreated aorta, the basal level of [3H]inositol monophosphate accumulation was significantly lower whereas [3H]phosphoinositide formation was significantly higher than in the saline-pretreated control aorta. Phenylephrine-, 5-hydroxytryptamine- and sodium fluoride-stimulated increases in [3H]inositol monophosphate accumulation were also significantly reduced in the aclarubicin-treated aorta compared to the control. Contractile forces induced by 5-hydroxytryptamine and sodium fluoride were markedly diminished in the aclarubicin-treated aorta. These results suggest that aclarubicin inhibits phosphatidylinositol hydrolysis at a level of phospholipase C activation, which is involved in the reduction of agonist-induced contraction of rat aorta.
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PMID:Aclarubicin inhibits phosphatidylinositol hydrolysis and contraction of rat aorta. 802 36

1. The effects of 8-bromoguanosine 3':5'-cyclic monophosphate (8-bromo-cyclic GMP) on phenylephrine-induced contractions and phosphatidylinositol (PI) hydrolysis were investigated in rat isolated caudal artery. The effects of the nucleotide were compared to those of felodipine, a dihydropyridine Ca2+ channel antagonist and ryanodine, a putative depletor of intracellular Ca2+ stores. The purpose of this investigation was to examine the regulatory effects of cyclic GMP on receptor-mediated signal transduction in vascular smooth muscle. 2. Phenylephrine induced a concentration-dependent increase in PI hydrolysis that reached a maximum at 10 microM phenylephrine. Pre-incubation with felodipine (10 nM) significantly reduced PI turnover, but did not affect basal hydrolysis. Similarly, removal of extracellular Ca2+ (2 mM ethylene glycol-bis(beta-amino-ethyl ether) N, N, N', N'-tetraacetic acid (EGTA)) blocked phenylephrine-induced PI hydrolysis, but did not affect basal turnover. In contrast, 8-bromo-cyclic GMP (10 microM) did not affect phenylephrine-induced PI hydrolysis, nor did it affect basal turnover. 3. Phenylephrine induced concentration-dependent contractions that were inhibited by each of 8-bromo-cyclic GMP (10 microM), felodipine (1 nM and 10 nM) and ryanodine (3 microM and 10 microM). In addition, removal of Ca2+ from the physiological salt solution (2 mM EGTA) completely abolished contractions elicited by phenylephrine. 4. Phenylephrine-induced contractions were not further affected by felodipine and 8-bromo-cyclic GMP applied concomitantly than by equivalent concentrations of felodipine alone. However, ryanodine and 8-bromo-cyclic GMP applied together significantly inhibited phenylephrine-induced contractions in comparison to ryanodine alone. 5 These results suggest that phospholipase C-activated PI hydrolysis in the rat caudal artery is dependent on extracellular Ca2+, mediated, in part, through dihydropyridine-sensitive Ca2+ channels.Inhibition of contraction by felodipine may be brought about through indirect inhibition of IP3 production and subsequent attenuation of intracellular Ca2+ release. 8-Bromo-cyclic GMP does not inhibit PI hydrolysis; it may regulate vascular smooth muscle contraction by inhibition of Ca2+ release from IP3-mediated intracellular stores, but it is unlikely that 8-bromo-cyclic GMP affects ryanodine-sensitive stores.
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PMID:Effects of 8-bromoguanosine 3':5'-cyclic monophosphate on phenylephrine-induced phosphatidylinositol hydrolysis and contraction in rat caudal artery. 856 40

The Na+/Ca2+ exchanger plays an important role in the maintenance of calcium homeostasis in the heart. Therefore, factors which regulate the exchanger have a significant impact on cardiac function. Previously, we showed that the non-hydrolysable GTP analog, 5'guanylyl imidodiphosphate [Gpp(NH)p], stimulates Na+/Ca2+ exchange activity, implying the involvement of a G protein in exchanger regulation. In this study, we examined the effect of G protein agonists on Na+/Ca2+ exchanger activity. Isoproterenol, a Gs agonist, had no effect on exchanger activity. Likewise, the Gi agonist, carbachol, did not influence Na+/Ca2+ exchanger activity. Since these G proteins couple to the adenylate cyclase system, it would appear that cAMP-linked events do not regulate the Na+/Ca2+ exchanger. We next examined the influence of Gq-linked agonists on exchanger activity. Phenylephrine, an alpha 1-adrenergic agonist, increased Na+/Ca2+ exchanger activity up to 111% with an EC50 of 21 microM. Moreover, the Na+/Ca2+ exchanger activity was enhanced by angiotensin II and endothelin 1, which caused maximal stimulation of exchanger activity up to 125% and 211%, respectively. The selective protein kinase C inhibitor chelerythrine significantly attenuated the ability of phenylephrine and angiotensin II to stimulate the Na+/Ca2+ exchanger. In addition, the protein kinase C activator, phorbol 12-myristate 13-acetate, stimulated exchanger activity by 32%, raising the possibility that all three Gq agonists mediate their actions in part through the promotion of phospholipase C activity and the subsequent activation of protein kinase C. The contribution of Na+/Ca2+ exchange to the actions of phenylephrine, angiotensin II, and endothelin 1 is discussed.
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PMID:Stimulation of the Na+/Ca2+ exchanger by phenylephrine, angiotensin II and endothelin 1. 874 10

1. The subtypes of alpha-adrenoceptor mediating the contractile responses of the cauda epididymis of the guinea-pig were investigated. The alpha 1-adrenoceptor agonist phenylephrine, but not the alpha 2-adrenoceptor agonist, xylazine (up to 10 microM), elicited concentration-dependent contractions from preparations of cauda epididymis (EC50 3.4 microM). The L-type Ca2+ channel antagonist, nifedipine (10 microM), reduced the maximal response to phenylephrine (by 77%). Preincubation of tissues with the alpha 1B-adrenoceptor-alkylating agent, chloroethylclonidine (50 microM, 30 min), shifted phenylephrine concentration-response curves to the right (4 fold) only when the alpha 2-adrenoceptor antagonist idazoxan (100 nM) was included during the pre-incubation with chloroethylclonidine. 2. Xylazine (1 microM) significantly shifted phenylephrine concentration-response curves to the left (3 fold); this effect was attenuated by idazoxan (100 nM). Both the incubation of preparations with nifedipine (10 microM) and the pre-incubation of preparations with chloroethylclonidine (50 microM, 30 min) attenuated the potentiating effects of xylazine (1 microM). Protection of alpha 2-adrenoceptors with idazoxan (100 nM) during the chloroethylclonidine (50 microM, 30 min) incubation restored the xylazine-mediated enhancement of phenylephrine concentration-response curves. Pertussis toxin (200 ng ml-1, 24 h) attenuated the xylazine (1 microM)-mediated potentiation of phenylephrine concentration-response curves. 3. Following the pre-incubation of preparations with chloroethylclonidine (50 microM, 30 min) 5-methylurapidil (10 nM to 3 microM) shifted phenylephrine concentration-response curves, in parallel, to the right with mean pKB values in the range of 8.27 (at 10 nM 5-methylurapidil) to 7.76 (at 3 microM 5-methylurapidil), the addition of idazoxan (100 nM) to the incubation medium did not significantly affect the 5-methylurapidil (10 to 300 nM) pKB values (8.41 to 7.64, respectively). In the presence of both idazoxan (100 nM) and nifedipine (10 microM), and following the pre-incubation with chloroethylclonidine (50 microM, 30 min), 5-methylurapidil (30 to 300 nM) still shifted phenylephrine concentration-response curves to the right (pKB values 7.77 to 7.36, respectively). 4. Phenylephrine (1 microM to 1 mM) increased the accumulation of [3H]-inositol phosphates (10 fold) in preparations of cauda epididymis (EC50 12 microM). This effect was sensitive to chloroethylclonidine pretreatment (50 microM, 30 min), antagonized with low affinity by 5-methylurapidil (- log pKi 7.8), but not potentiated by xylazine (1 microM). Xylazine (10 nM - 100 microM) reversed the forskolin (10 or 30 microM) stimulated accumulation of [3H]-adenosine 3':5'-cylic monophosphate (cyclic AMP) in preparations of cauda epididymis (by approximately 45%). Incubation of tissues with both pertussis toxin (200 ng ml-1, 24 h) and pertussis toxin vehicle increased the basal activity of adenylate cyclase (3 fold) but did not increase the capacity of forskolin (30 microM) to stimulate the accumulation of [3H]-cyclic AMP in these tissues. Xylazine did not significantly inhibit the forskolin-stimulated accumulation of [3H]-cyclic AMP in either vehicle or pertussis toxin treated tissues. 5. These studies indicate that the epididymis of the guinea-pig contains alpha 1- and alpha 2-adrenoceptors. On the basis of the actions of chloroethylclonidine and 5-methylurapidil the alpha 1-adrenoceptors of this tissue may be of the alpha 1A- and alpha 1B-subtypes and are linked to both the influx of extracellular Ca2+ and to phospholipase C. The alpha 2-adrenoceptors of this tissue are negatively coupled to adenylate cyclase, sensitive to pertussis toxin, but do not amplify phenylephrine-stimulated [3H]-inositol phosphate accumulation. Stimulation of the alpha 2-adrenoceptors of this tissue may selectively potentiate the influx of extracellular Ca2+.
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PMID:Alpha-adrenoceptor mediated responses of the cauda epididymis of the guinea-pig. 893 24

This study demonstrates that alpha1-adrenergic receptors previously identified in the pregnant rat myometrium are heterogeneous. They can be subtyped alpha1A- and alpha1B-adrenergic receptors on the basis of their affinity for the antagonists WB4101 (alpha1A > alpha1B) and chloroethylclonidine (alpha1B selective). Between Day 21 of pregnancy and term, the proportion of [3H]prazosin binding sites with low affinity for WB4101 and sensitive to inactivation by 10(-5) M chloroethylclonidine under hypotonic conditions (alpha1B subtype) remained constant. In contrast, the number of [3H]prazosin binding sites with a high affinity for WB4101 and insensitive to chloroethylclonidine (alpha1A subtype) increased by 88% at term. The effect of 5'-guanylylimidodiphosphate (Gpp[NH]p) on competition of the agonist phenylephrine for [3H]prazosin binding in the presence of WB4101 or after chloroethylclonidine pretreatment indicates that the alpha1A-adrenergic receptor underwent uncoupling whereas the alpha1B-adrenergic receptor-G protein coupled state was increased (+ 63%). Phenylephrine consistently stimulated phospholipase C activity on membrane fractions prepared from term myometria. This stimulation was completely inhibited after 10(-5) M chloroethylclonidine but was not consistently decreased with 5-methylurapidyl, a selective alpha1A-antagonist. Furthermore QL antibody (anti-G alpha(q)/G alpha11) also specifically blocked the phenylephrine-stimulated phospholipase C activity. Altogether these results strongly suggest that activation of the alpha1B-adrenergic receptor subtype in the pregnant myometrium at term may contribute to the stimulation of the G alpha(q)/G alpha11/phospholipase C signaling pathway.
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PMID:The alpha1B-adrenergic receptor subtype activates the phospholipase C signaling pathway in rat myometrium at parturition. 936 85


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