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:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The H1-histamine receptor antagonist [3H]mepyramine bound with high affinity (Kd = 3-5 nM) to membranes derived from 1321N1 human astrocytoma cells. The H1-receptor antagonists triprolidine and diphenhydramine inhibited [3H]mepyramine binding with Kj values of 1-5 nM, whereas the Kj of the H2-histamine receptor antagonist cimetidine was greater than 100 microM. Histamine also inhibited [3H]mepyramine binding to 1321N1 cell membranes, and the histamine inhibition curve was shifted to the right and steepened in the presence of 1 microM guanosine 5'-O-(3-thiotriphosphate). Treatment of 1321N1 cells with pertussis toxin had no effect on the capacity of histamine to inhibit [3H]mepyramine binding either in the absence or presence of guanosine 5'-O-(3-thiotriphosphate). Therefore, agonist-occupied histamine receptors in these cells apparently interact with a guanine nucleotide regulatory protein that is not the inhibitory guanine nucleotide regulatory protein of adenylate cyclase. Although adenylate cyclase activity was not affected by histamine in a cell-free preparation, incubation of 1321N1 cells with histamine resulted in an attenuation of cyclic AMP accumulation. Analysis of cyclic AMP degradation in the presence of histamine indicated that the effects of histamine on cyclic AMP accumulation are mediated through activation of phosphodiesterase. This idea was supported by the fact that the phosphodiesterase inhibitor 1-isobutyl 3-methylxanthine blocked attenuation of cyclic AMP accumulation by histamine in a noncompetitive manner. Histamine also markedly increased phosphoinositide breakdown and 45Ca2+ efflux in 1321N1 cells. These histamine-induced effects apparently are mediated through H1-receptors, since triprolidine, but not cimetidine, potently inhibited histamine action. As for histamine interaction with its receptor, pertussis toxin had no effect on histamine-induced phosphoinositide breakdown, 45Ca2+ efflux, or attenuation of cyclic AMP accumulation. Taken together, these data indicate that 1321N1 human astrocytoma cells are a useful model system for the study of H1-histamine receptors and the biochemical responses mediated through these receptors.
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PMID:H1-histamine receptors on human astrocytoma cells. 241 44

An adenosine receptor has been characterized to unambiguously demonstrate that the inhibitory guanine nucleotide regulatory protein, Gi, of 1321N1 human astrocytoma cells is fully capable of functionally coupling to adenylate cyclase. Adenosine receptor agonists attenuated cyclic AMP accumulation by 35 to 75% with the order of potency of N6(R-phenylisopropyl)-adenosine greater than adenosine = 2-chloroadenosine greater than N6-methyladenosine = N6-benzyladenosine. 3-Isobutyl-1-methylxanthine competitively antagonized the effect of adenosine receptor agonists. Adenylate cyclase activity measured in cell-free preparations from 1321N1 cells was inhibited by N6(R-phenylisopropyl)-adenosine. Pretreatment of 1321N1 cells with pertussis toxin blocked both adenosine receptor-mediated inhibition of adenylate cyclase activity and attenuation of cyclic AMP accumulation. In contrast to the effects on responses to adenosine receptor agonists, 3-isobutyl-1-methylxanthine noncompetitively antagonized muscarinic receptor-mediated attenuation of cyclic AMP accumulation and pertussis toxin had no effect. These data are consistent with the ideas that Gi is fully functional in 1321N1 cells and links inhibitory adenosine receptors to adenylate cyclase, and that the muscarinic receptor of these cells couples to the phosphoinositide response system, but is incapable of functionally coupling through Gi to inhibit adenylate cyclase.
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PMID:Adenosine and muscarinic cholinergic receptors attenuate cyclic AMP accumulation by different mechanisms in 1321N1 astrocytoma cells. 242 Sep 67

Adenylate cyclase from a spruce budworm cell line, IBRI-Cfl, is activated by octopamine (Ka = 50 microM), guanine nucleotides and sodium fluoride but not by forskolin. In addition, forskolin does not potentiate the octopamine-sensitive response. To our knowledge, this is the first published report of a hormone-sensitive adenylate cyclase, with a functional guanine nucleotide regulatory protein, that is insensitive to forskolin both in intact cells and washed membrane preparations.
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PMID:Forskolin-insensitive adenylate cyclase in cultured cells of Choristoneura fumiferana (Insecta). 244 Apr 27

Stimulation of P2-purinergic receptors by ATP resulted in activation of phosphorylase, which was associated with marked production of inositol trisphosphate (Ins-P3), in rat hepatocytes. ATP also inhibited forskolin-induced accumulation of cAMP in the presence of a phosphodiesterase inhibitor. On the contrary, adenosine or AMP never inhibited the cAMP accumulation, but increased hepatocyte cAMP; the stimulation was antagonized by a methylxanthine. Thus, P1-purinergic receptors are linked to adenylate cyclase in a stimulatory fashion in hepatocytes. Various kinds of purine nucleotides stimulating P2-receptors can be divided into two groups on the basis of their relative abilities to stimulate Ins-P3 production and to inhibit cAMP accumulation; the first group including adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ADP, 5-adenylyl imidodiphosphate, GTP, and guanosine 5'-O-(3-thiotriphosphate) has an efficacy similar to that of ATP, and the second group of nucleotides including alpha, beta-methyleneadenosine 5'-triphosphate, beta, gamma-methyleneadenosine 5'-triphosphate (App(CH)2)p), and GDP exerts considerable inhibitory effects on cAMP accumulation, but only slight effects on inositol lipid metabolism. Treatment of hepatocytes with islet-activating protein, pertussis toxin, blocked the nucleotide-induced inhibition of cAMP accumulation, but exerted only a small effect on Ins-P3 production. In membranes prepared from hepatocytes, forskolin-stimulated adenylate cyclase was inhibited by GTP. This GTP-induced inhibition of the enzyme was susceptible to islet-activating protein and dependent on the concentration of ATP (or its derivatives, ATP gamma S or App(CH2)p). It is concluded that there are two types of P2-purinergic receptors: one is linked to adenylate cyclase via an inhibitory guanine nucleotide regulatory protein (Gi) and the other is linked to phospholipase C.
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PMID:P2-purinergic receptors are coupled to two signal transduction systems leading to inhibition of cAMP generation and to production of inositol trisphosphate in rat hepatocytes. 244 92

The methylxanthines, such as caffeine and theophylline, are an important and widely used class of drugs, which are believed to mediate many of their physiological effects by increasing intracellular concentrations of cAMP. These agents are known to inhibit phosphodiesterases and to block inhibitory A1 adenosine receptors in a competitive manner. Thus, the methylxanthines may increase cAMP accumulation by slowing its inactivation or by enhancing its production. Using a rat adipocyte membrane model we demonstrate that isobutylmethylxanthine (IBMX) induces a dose-dependent 34% increase in cAMP production above that produced by complete phosphodiesterase inhibition with papaverine. This stimulatory effect is dependent upon the inhibitory guanine nucleotide regulatory protein G1, in that inactivation of Gi by pertussis intoxication ablates IBMX-mediated stimulation of adenylate cyclase activity. Because the Gi-dependent effect of IBMX results in increased cAMP production, the mode of action is likely blockade of Gi activity. Accordingly, the capacity of GTP itself to inhibit adenylate cyclase activity is attenuated by IBMX. In contrast to Gi blockade induced by pertussis toxin, this heretofore unappreciated stimulatory mechanism is completely reversed by inhibitory receptor agonists. This mechanism of action may be responsible for certain physiological effects of methylxanthines, which are not easily explained by phosphodiesterase inhibition or antagonism of A1 adenosine receptors.
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PMID:Isobutylmethylxanthine stimulates adenylate cyclase by blocking the inhibitory regulatory protein, Gi. 245 59

We used pertussis toxin to study the mechanism(s) by which divalent cations lower cellular cAMP content in bovine parathyroid cells. In cultured parathyroid cells, high extracellular Ca2+ (5 mM) or Mg2+ (5-10 mM) lowers dopamine-stimulated cAMP content by 70-90%. Pertussis toxin (0.5 microgram/ml) totally blocks the inhibitory effects of Ca2+ and Mg2+ on cAMP content. Ba2+ and Sr2+ (5 mM) also lower cAMP content by 80-90%, and this effect is, likewise, blocked by pertussis toxin. Pretreatment with pertussis toxin had no effect on the release of cAMP into the extracellular fluid. The toxin also did not modify phosphodiesterase activity in sonicates of parathyroid cells (42.68 +/- 3.26 vs. 47.00 +/- 2.82 pmol cAMP hydrolyzed/10(6) cells.20 min in control and toxin-treated cells, respectively). Moreover, addition of the phosphodiesterase inhibitor isobutyl-methylxanthine did not modify the inhibition of dopamine-stimulated cAMP accumulation by 5 mM Ca2+ in control cells (85% vs. 86% inhibition, respectively, with and without isobutylmethylxanthine). Pertussis toxin-catalyzed ADP ribosylation in homogenates of control cells demonstrated the presence of two substrates with mol wt of 40K and 41K. Preexposure of cells to pertussis toxin overnight resulted in the complete loss of both substrates on subsequent ADP ribosylation with [32P]NAD. Pertussis toxin pretreatment did not enhance adenylate cyclase activity indirectly via reducing the extracellular Ca2+-induced rise in cytosolic Ca2+, since the cytosolic Ca2+ level at 5 mM Ca2+ was about 60% higher in pertussis toxin-treated than in control cells (531 +/- 85 vs. 326 +/- 35 nM; P less than 0.05). In addition, ionomycin had no significant effect on cellular cAMP levels in control cells despite increasing the cytosolic Ca2+ concentration to levels as high as 1700 nM at 10(-5) M. Thus, changes in cytosolic Ca2+ phosphodiesterase activity, or efflux of cAMP from the cell cannot explain the inhibition of cAMP accumulation by divalent cations or the reversal of this effect by pertussis toxin. Instead, the present data suggest that extracellular divalent cations modulate the formation of cellular cAMP in parathyroid cells by a process involving a pertussis toxin-sensitive guanine nucleotide regulatory protein, presumably inhibition of adenylate cyclase by Gi via a receptor-like mechanism.
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PMID:Divalent cations suppress 3',5'-adenosine monophosphate accumulation by stimulating a pertussis toxin-sensitive guanine nucleotide-binding protein in cultured bovine parathyroid cells. 246 88

Rabbit myometrium contains postsynaptic alpha-1, alpha-2, and beta-2 adrenoreceptors. The response to endogenous catecholamines depends on the summation of interactions at these receptors and is influenced by the hormonal environment. Estrogen treatment of ovariectomized rabbits increases the alpha adrenergic contractile response whereas progesterone treatment of estrogen primed animals results in a predominance of the beta adrenergic response, which is inhibition of contractions. Of the receptor subtypes, only the alpha-2 receptor concentration is increased at physiological estrogen concentrations. However, alpha-2 receptors have not been shown to be directly involved in myometrial contraction, which appears to be mediated solely by alpha-1 adrenergic interactions. To test whether alpha-2 receptors might indirectly affect contraction by opposing interactions at the beta receptor, we examined the ability of alpha adrenergic stimulation to reduce myometrial cyclic adenosine 3',5'-monophosphate (cAMP) generation. We find that alpha-2 receptors inhibit myometrial ade adenylate cyclase through the guanine nucleotide regulatory protein, Gi. In addition, we find that activation of alpha-1 receptors also reduces cAMP generation. This interaction, which can be demonstrated in the absence but not the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, does not appear to be mediated through Gi. These findings illustrate the complexity of adrenergic interactions in tissues containing several adrenergic subtypes.
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PMID:Alpha adrenergic stimulation reduces cyclic adenosine 3',5'-monophosphate generation in rabbit myometrium by two mechanisms. 246 19

The effect of angiotensin II (AII) on adenylate cyclase was studied in the rat and rabbit heart sarcolemma. AII inhibited adenylate cyclase activity in the rat and rabbit sarcolemma in a concentration-dependent manner. Maximal inhibition of about 35-40% was observed in the rat, with an apparent Ki of about 3 nM; about 30% inhibition, with an apparent Ki of about 6 nM, was noted in rabbit sarcolemma. The inhibitory effect of AII was dependent on the presence of guanine nucleotides and was blocked by saralasin. In addition, AII also inhibited the stimulatory effects of isoproterenol and glucagon on adenylate cyclase. Ninhibin, a sperm factor which has been shown to modify the characteristics of inhibitory guanine nucleotide regulatory protein (Gi), attenuated the inhibitory effects of AII on basal and hormone-sensitive adenylate cyclase. Furthermore, pertussis toxin (PT) treatment of the sarcolemma in the presence of [32P]NAD resulted in ADP-ribosylation of a single 41-kD protein. PT also attenuated the AII-mediated inhibition of basal and hormone-sensitive adenylate cyclase and enhanced the magnitude of the stimulatory effects of isoproterenol and glucagon on adenylate cyclase activity. These data suggest that the rat myocardial sarcolemma contains AII receptors that are negatively coupled to adenylate cyclase through Gi protein.
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PMID:Angiotensin II receptors negatively coupled to adenylate cyclase in rat myocardial sarcolemma. Involvement of inhibitory guanine nucleotide regulatory protein. 249 5

The dopamine (DA) D-1 and D-2 receptors coupled to adenylate cyclase in the rat retina were characterized pharmacologically. In confirmation of reports using other neural tissues, activation of D-1 receptors with DA, apomorphine or SKF 38393 resulted in activation of adenylate cyclase and enhanced accumulation of cyclic AMP (cAMP). The response to DA was blocked by SCH 23390, a D-1 receptor antagonist. D-2 receptors negatively coupled to adenylate cyclase were demonstrated by preincubating retina with SCH 23390 and then with DA or apomorphine. D-2 receptor responses were also elicited with quinpirole or bromocriptine, D-2 receptor agonists, in the absence of SCH 23390. (+)-Butaclamol, but not (-)-butaclamol, blocked the D-2 receptor-induced decrease of cAMP. Moreover, I-sulpiride was more active than d-sulpiride in reversing the DA-induced inhibition of cAMP accumulation. D-1 and D-2 receptor responses were also evident in forskolin-activated retina. The intraocular injection of pertussis toxin prevented the fall of cAMP and enhanced the rise of cAMP by DA, indirectly implicating the need for a guanine nucleotide regulatory protein in the process. Our results demonstrate that retinal tissue contains DA receptors that are similar to those found in brain and they imply that therapeutic agents that interact with the receptors in brain might interact with the receptors in retina.
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PMID:Pharmacological characterization of rat retinal dopamine receptors. 249 95

Brief exposure of hepatocytes to glucagon, angiotensin or the protein kinase C activator TPA (12-O-tetradecanoylphorbol 13-acetate) caused the inactivation of the inhibitory guanine nucleotide regulatory protein Gi. Glucagon-mediated desensitization of glucagon-stimulated adenylate cyclase activity was seen in hepatocytes from both normal rats and those made diabetic with streptozotocin, where Gi is not functionally expressed. Normal glucagon desensitization was seen in hepatocytes from young animals, 6 weeks of age, which had amounts of Gi in their hepatocyte membranes which were some 45% of that seen in mature animals (3.4 pmol/mg of plasma-membrane protein). Streptozotocin-induced diabetes in young animals abolished the appearance of functional Gi in hepatocyte plasma membranes. Pertussis-toxin treatment of hepatocytes from both normal mature animals and those made diabetic, with streptozotocin, blocked the ability of glucagon or angiotensin or TPA to elicit desensitization of adenylate cyclase. The isolated B (binding)-subunit of pertussis toxin was ineffective in blocking desensitization. Neither induction of diabetes nor treatment of hepatocytes with pertussis toxin inhibited the ability of glucagon and angiotensin to stimulate the production of inositol phosphates in intact hepatocytes. Thus (i) Gi does not appear to play a role in the molecular mechanism of glucagon desensitization in hepatocytes, (ii) the G-protein concerned with receptor-stimulated inositol phospholipid metabolism in hepatocytes appears not to be a substrate for the action of pertussis toxin, (iii) in intact hepatocytes, treatment with glucagon and/or angiotensin can elicit the inactivation of the inhibitory G-protein Gi, and (iv) pertussis toxin blocks desensitization by a process which does not involve Gi.
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PMID:Glucagon desensitization of adenylate cyclase and stimulation of inositol phospholipid metabolism does not involve the inhibitory guanine nucleotide regulatory protein Gi, which is inactivated upon challenge of hepatocytes with glucagon. 249 30


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