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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human erythroleukemia cells are a model system for studies of alpha 2-adrenergic receptors and their coupling to inhibition of adenylate cyclase (McKernan, R. M., Howard, M. J., Motulsky, H. J., and Insel, P. A. (1987) Mol. Pharmacol. 32, 258-265). Using Fura-2, we show that alpha 2-adrenergic receptor stimulation also increases intracellular Ca2+ in these cells by 80-250 nM. Although epinephrine only inhibited forskolin-stimulated cAMP generation when beta-adrenergic receptors were blocked, the Ca2+ increase was not affected by beta-adrenergic receptor blockade. The Ca2+ increase was not affected by forskolin or 8-bromo-cAMP. Thus, alpha 2-adrenergic receptors independently couple to elevation of intracellular Ca2+ and adenylate cyclase inhibition. Chelating all extracellular Ca2+ did not reduce the response, demonstrating mobilization of intracellular, rather than influx of extracellular Ca2+. The epinephrine-stimulated Ca2+ mobilization occurred prior to any detectable increase in inositol-(1,4,5)-trisphosphate. It was abolished by pretreatment with pertussis toxin (which blocks some G protein-mediated processes), but not by aspirin and indomethacin (which inhibit cyclooxygenase), nordihydroguaiaretic acid (which inhibits lipoxygenase), or Na+-free buffer (to block any Na+H+ exchange). We conclude, therefore, that alpha 2-adrenergic receptors on human erythroleukemia cells couple to mobilization of intracellular Ca2+ via a (pertussis toxin-sensitive) G protein-mediated mechanism that is independent of inhibition of adenylate cyclase.
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PMID:Alpha 2-adrenergic receptor stimulation mobilizes intracellular Ca2+ in human erythroleukemia cells. 256 96

Results of our consecutive study on the pathogenic mechanism underlying ischemic brain edema are summarized in this paper. Pertinent findings are as follows: (1) there is a close correlation between the influxes of water and sodium following ischemia; (2) the edema fluid can be regarded as the ultrafiltrate of serum; (3) there is a significant increase in the brain content of HETEs following ischemia; (4) the lipoxygenase activity of brain microvessels is increased following ischemia; (5) the lipoxygenase activity as well as the Na+, K+-ATPase activity of brain microvessels are enhanced by a hydroperoxide, 15-HPETE; (6) inhibition of Na+, K+-ATPase of brain microvessels by intraarterial infusion of ouabain resulted in a significant decrease in edema formation; and (7) not the cyclooxygenase, but the lipoxygenase pathway seems to be involved in the enhancement of microvessel Na+, K+-ATPase. Lipoxygenase(s) and Na+-K+-ATPase of brain microvessels, the activities of which are enhanced by an increased level of free radicals and/or hydroperoxides, may play a significant role in the occurrence of ischemic brain edema.
Mol Chem Neuropathol 1989 Apr
PMID:The role of free radicals and eicosanoids in the pathogenetic mechanism underlying ischemic brain edema. 266 83

The effects of CGS 13080, a thromboxane (TXA2) synthase inhibitor, on airway responses to arachidonic acid (AA) were investigated in the anesthetized cat. Feline and human lung microsomal fraction exhibited prostaglandin I2 (PGI2, prostacyclin), and TXA2 synthase activities, and human platelet microsomal fractions exhibited TXA2 synthase activity. Cat and human lung microsomal fractions, but not human platelets, exhibited the presence of GSH-dependent PGE2 isomerase activity. CGS 13080 inhibited TXA2 synthase activity in all three microsomal fractions in a concentration-dependent manner. The increases in transpulmonary pressure and lung resistance and decreases in dynamic compliance in response to AA were decreased significantly by CGS 13080. These data suggest that the bronchoconstrictor actions of AA are mediated in large part by the formation of TXA2. The data further indicate that cyclooxygenase products other than TXA2 are involved in the bronchoconstrictor response to AA since meclofenamate had greater inhibitory activity than did CGS 13080. Moreover, the effects of CGS 13080 were due to inhibition of TXA2 synthase rather than an effect on TXA2 receptors, since airway responses to the TXA2 mimic, U46619, were not altered. The present data show that CGS 13080 inhibits TXA2 synthase activity without altering cyclooxygenase, PGI2 synthase, or GSH-dependent PGE2 isomerase activities. The data further indicate that in vivo administration of CGS 13080 may selectively increase PGI2 synthase activity.
Mol Cell Biochem 1989 Jan 23
PMID:Inhibition of pulmonary thromboxane A2 synthase activity and airway responses by CGS 13080. 272 78

We examined the mechanisms by which the phospholipid-sensitive, calcium-dependent protein kinase (protein kinase C) regulates prostacyclin synthesis by ovarian cells. In monolayer cultures of swine granulosa cells, specific phorbol esters significantly augmented production of the stable immunoreactive metabolite of prostacyclin, 6-keto-prostaglandin F1 alpha by 3- to 8-fold. These stimulatory actions were dose (0.03-30 ng/ml) and time (24-96 h) dependent, could be reproduced by non-diterpene activators of protein kinase C, and were corroborated by high performance liquid chromatography and mass spectrometry. The rank order of potency of phorbol esters was 12-O-tetradecanoylphorbol 13-acetate (TPA) greater than phorbol 12,13-dibenzoate greater than phorbol 12,13-dibutyrate greater than pure phorbol base. TPA enhanced de novo synthesis of prostacyclin, and synergized with the divalent cation ionophore, A23187. Although prostacyclin synthetase activity was not induced, microsomal cyclooxygenase activity was significantly increased by phorbol treatment. Moreover, TPA doubled the intracellular accumulation of free arachidonic acid. An inhibitor of phospholipase A2 (quinacrine 100 microM) impeded, whereas melittin (0.01 microM), an activator of cellular phospholipase A2, and purified bacterial phospholipase A2 (5 and 50 mU/ml) both augmented prostacyclin production. RH 59022 (30 microM), an inhibitor of diacylglyceride lipase, also suppressed prostacyclin synthesis. We conclude that the protein kinase C effector pathway is functionally coupled to de novo prostacyclin production in the swine granulosa cell. Increased eicosanoid synthesis can be accounted for by enhanced phospholipase A2 and diacylglyceride lipase-mediated availability of arachidonic acid substrate and an activated cyclooxygenase enzyme without a change in prostacyclin synthetase activity.
Mol Cell Endocrinol 1989 May
PMID:Mechanism(s) by which activation of protein kinase C is coupled to prostacyclin synthesis in granulosa cells. 275 27

Prostaglandin H synthase (PHS) hydroperoxidase-mediated metabolism of phenylbutazone and the relationship of this metabolism to the inhibition of PHS cyclooxygenase by phenylbutazone was investigated. Phenylbutazone was metabolized to several intermediates and metabolites. A phenylbutazone carbon-centered radical (aN = 14.6 G) formed by PHS hydroperoxidase was trapped by 2-methyl-2-nitrosopropane and detected by ESR in incubations with ram seminal vesicle microsomes. 4-Hydroperoxy- and 4-hydroxyphenylbutazone were isolated from incubations of phenylbutazone with either ram seminal vesicle microsomes or horseradish peroxidase. Phenylbutazone (100 microM-2 mM) inhibited PHS cyclooxygenase in incubations of PHS apoenzyme reconstituted with hematin. Phenylbutazone (5-250 microM) did not inhibit PHS cyclooxygenase in incubations of PHS apoenzyme reconstituted with manganese protoporphyrin IX, which lacks hydroperoxidase activity. Thus, metabolism of phenylbutazone by PHS hydroperoxidase is required for it to inhibit PHS cyclooxygenase. 4-Hydroperoxy- and 4-hydroxyphenylbutazone were ineffective inhibitors of PHS cyclooxygenase. Other hydroperoxides that easily rearrange to peroxyl radicals were potent inhibitors of PHS cyclooxygenase, suggesting that the phenylbutazone peroxyl radical may be the inhibitor. 4-Hydroperoxyphenylbutazone was not reduced to 4-hydroxyphenylbutazone by PHS hydroperoxidase. We propose that 4-hydroxyphenylbutazone formation occurs by a nonenzymatic reaction of two phenylbutazone peroxyl radicals and their subsequent rearrangement to alkoxy radicals, which abstract hydrogen atoms. Our data indicate the importance of PHS hydroperoxidase in the inactivation of PHS cyclooxygenase by peroxides.
Mol Pharmacol 1988 Aug
PMID:Prostaglandin hydroperoxidase-dependent oxidation of phenylbutazone: relationship to inhibition of prostaglandin cyclooxygenase. 284 54

Carbon monoxide (CO) inhibits human platelet aggregation triggered with threshold levels of agonists like arachidonate, ADP, collagen, thrombin, or the prostaglandin endoperoxide analogue U46619. This inhibition is counteracted by illumination with light above 400 nm indicating the involvement of a ferrous hemoprotein. An earlier suggestion that the mechanism of CO inhibition involves the cytochrome P450 protein thromboxane A2 synthase was ruled out as well as the involvement of the iron containing enzymes like cyclooxygenase or 12-lipoxygenase. In the presence of CO, no arachidonate was released from phospholipids, no increase of intracellular calcium levels was observed, and phospholipase C was not activated suggesting that the transducing mechanisms from the receptors to phospholipase C was effected in the presence of CO. cAMP levels were also unchanged but cGMP levels showed an increase of about 30%. By comparison with the guanylate cyclase stimulator nitroprusside, it was shown that such levels could block aggregation. In a 10,000 X g supernatant, CO enhanced guanylate cyclase activity 4-fold, supporting the view that CO acts by increasing platelet cGMP levels. With respect to the mechanism of guanylate cyclase action, the binding of CO to the regulatory subunit of guanylate cyclase must be responsible for the observed activation. It is concluded that cGMP is an important feedback regulator of the Pl response and that already a 25% increase in its steady state levels can cause inhibition of platelet aggregation.
Mol Pharmacol 1987 Oct
PMID:Inhibition of platelet aggregation by carbon monoxide is mediated by activation of guanylate cyclase. 289 93

Experiments with primary cultures of isolated porcine thyroid follicles were performed in serum-free well-defined medium to investigate different pathways that may be involved in the regulation of thyroid cell growth. The incorporation of [3H]thymidine into DNA within 72 h was about 25-fold with fetal calf serum (FCS, 1%), 20-fold with epidermal growth factor (EGF, 1 ng/ml) and 3.5-fold with insulin (10 micrograms/ml) as compared to controls. Bovine TSH significantly reduced the basal and insulin-induced growth rate at concentrations of 10(-6) to 10(-4) U/ml and 10(-4) U/ml, respectively. Forskolin stimulated cyclic AMP accumulation in thyroid cells and significantly reduced FCS-, EGF- or insulin-induced growth. In contrast, a 2- to 7-fold increase in FCS-, insulin- or EGF-induced growth rate was found, when cyclic AMP formation was inhibited by 2',5'-dideoxyadenosine (DDA). Iodide was stimulatory at low concentrations (1 microM) and inhibitory at higher concentrations (40-80 microM) on FCS-induced growth rate. The inhibitory effect of iodide was blocked by propylthiouracil (PTU), indicating that an iodinated compound is responsible for this effect. Indomethacin, a cyclooxygenase inhibitor, did not inhibit EGF- and insulin-induced growth up to a concentration of 100 microM. However, nordihydroguaiaretic acid (NDGA) and BW-755C, which are lipoxygenase inhibitors, strongly inhibited the growth of thyroid cells at micromolar concentrations. These data clearly show that (1) bovine TSH is not a growth factor for isolated thyroid cells in vitro, (2) thyroid cell proliferation, induced by FCS, EGF and insulin is under negative control of cyclic AMP. (3) Iodide controls dose-dependently thyroid cell growth by iodinated metabolites, probably modulating 2 different pathways: (a) at low iodide concentrations, an iodinated compound enhances the growth rate by inhibition of cyclic AMP formation, and (b) at high concentrations, iodide diminishes the growth rate by inhibiting the response to growth factors. (4) Metabolite(s) of lipoxygenase appear to be involved in intracellular signal transduction evoked by growth factors in thyroid cells.
Mol Cell Endocrinol 1985 Sep
PMID:Involvement of cyclic AMP, iodide and metabolites of arachidonic acid in the regulation of cell proliferation of isolated porcine thyroid follicles. 299 5

Previous investigations in this laboratory have indicated that arachidonic acid stimulates a rapid, dose-dependent, and reversible increase in human placental lactogen (hPL) release which is not dependent on cyclooxygenase or lipoxygenase metabolism. To investigate further the mechanism by which arachidonic acid stimulates the release of hPL, the effects of arachidonic acid on phosphoinositide hydrolysis were examined in an enriched cell culture population of term human syncytiotrophoblast. Phosphoinositide hydrolysis was assayed by three methods: the release of 3H from perfused cells prelabeled with [3H]myoinositol, the measurement of inositol phosphate accumulation, and the distribution of radioactivity in phospholipids separated by two-dimensional thin layer chromatography after exposure of 32P-labeled placental cells to arachidonic acid. Arachidonic acid stimulated a concentration-dependent, rapid, and reversible increase in the release of both [3H]myoinositol and hPL from perfused placental cells. This effect was not inhibited by prior incubation of cells with indomethacin (20 microM). In contrast, palmitic acid and oleic acid stimulated phosphoinositide hydrolysis only at a high concentration (100 microM). Arachidonic acid also stimulated the rapid appearance of inositol monophosphate in placental cells. The effect of arachidonic acid was specific for hydrolysis of phosphoinositides and phosphatidylserine and did not involve other phospholipids. Since phosphoinositide hydrolysis is associated with hormone release in a variety of secretory systems, these results suggest that the stimulation of hPL release by arachidonic acid may be mediated, at least in part, by the activation of phospholipase C.
Mol Pharmacol 1985 Dec
PMID:Arachidonic acid stimulates phosphoinositide hydrolysis and human placental lactogen release in an enriched fraction of placental cells. 300 98

The effects of agents that cause vasodilatation and hypotension, such as endogenously produced bradykinin (BK) or the drug nitroprusside (NP), appear to result from effects on cyclic nucleotides (cGMP, cAMP) and arachidonate metabolism. Cultured human fibroblasts, which possess B2 BK receptors and respond to NP with an increase in cGMP, were used to study the interaction of these agents at the molecular level. Addition of BK or NP to cultured human fibroblasts caused a rapid increase in cGMP. The effect of NP was usually maximal within 30 sec, after which cGMP content declined. The increase in cGMP produced by BK reached a maximum at approximately 1 min and then fell; the rise with NP was more than 10 times that with BK. At 30 sec, cGMP content with NP plus BK was less than with NP alone. At later times, however, effects of BK and NP were slightly more than additive and maximal cGMP levels were reached at 90 sec. BK increased prostaglandin production by the fibroblasts; it is believed that the kinin-induced elevation in cAMP content is secondary to increased prostaglandin formation. NP caused a small, early increase in cAMP without significant effect on prostaglandin I2 (PGI2); after 2.5 min, effects on PGI2 and cAMP were greater with BK and NP than with BK alone. To study further the roles of arachidonate metabolites in the fibroblast response to BK and NP, the cyclooxygenase inhibitor, indomethacin, and the combined lipoxygenase and cyclooxygenase inhibitor, 5,8,11,14-eicosatetraynoic acid (ETYA), were added to fibroblasts prior to BK or NP. Increases in cAMP or PGI2 with BK or BK plus NP were blocked by indomethacin or ETYA. These effects of BK or BK plus NP on cAMP thus appear to be mediated through cyclooxygenase products of arachidonate metabolism. Indomethacin and ETYA did not affect cGMP in the presence of BK plus NP but enhanced NP-stimulated cGMP accumulation by 40-50%; effects of NP on cGMP may be independent of or perhaps inhibited by cyclooxygenase derivatives. Cellular responses to BK plus NP differed quantitatively and temporally from the sum of effects of BK and NP alone. Through interactions of this type, in vivo responses to drugs like NP may be influenced by levels of BK or similar endogenous mediators.
Mol Pharmacol 1986 Sep
PMID:Effects of nitroprusside on the bradykinin responsiveness of human fibroblasts. 301 83

Addition of leukotriene D4 (LTD4) to [3H]myo-inositol-labeled guinea pig lung induced rapid breakdown of inositol lipids. Formation of [3H]inositol trisphosphate was rapid, with a peak of 140-160% of the control level, 30 sec post-treatment. Formation of [3H]inositol bisphosphate and [3H]inositol monophosphate ([3H]IP1) was also rapid in the presence of LiCl. LTD4-induced [3H]IP1 formation was concentration dependent, stereoselective, and not inhibited by the cyclooxygenase inhibitor, indomethacin. Agonist analogs of LTD4 and leukotriene E4 also induced dose-dependent increases in the synthesis of [3H]IP1. The rank order potency of the agonist-induced [3H]IP1 formation was equivalent to those reported for LTD4 receptor binding, smooth muscle contraction, and thromboxane B2 biosynthesis. Furthermore, a specific receptor antagonist, SKF 102922, inhibited LTD4-induced [3H]IP1 formation in guinea pig lung. These studies suggest that LTD4 may interact with membrane receptor and activate a phospholipase C, which in turn induces the hydrolysis of inositol lipids. The hydrolysis products, diacylglycerol and inositol trisphosphate, can be regarded as the intracellular messengers for LTD4 receptors in guinea pig lung. This concept may explain a variety of pharmacological effects of leukotrienes in different types of target cells or tissues.
Mol Pharmacol 1987 Jan
PMID:Leukotriene-induced hydrolysis of inositol lipids in guinea pig lung: mechanism of signal transduction for leukotriene-D4 receptors. 302 24


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