Showing papers on "Cyclase published in 1980"
949 citations
TL;DR: This Nle4, D-Phe7 synthetic analogue of alpha-MSH is a very porent melanotropin, 26 times as potent as alpha- MSH in the adenylate cyclase assay, and the resistance of the peptide to enzymatic degradation and its extraordinarily potent and prolonged biological activity should make this analogue ofalpha-MSh an important molecular probe for studying the melanotropic receptors of both normal and abnormal (melanoma) melanocytes.
Abstract: alpha-Melanocyte-stimulating hormone (alpha-MSH) reversibly darkens frog skins by stimulating melanosome movement (dispersion) within melanophores. Heat-alkali treatment of alpha-MSH results in prolonged biological activity of the hormone. Quantitative gas chromatographic analysis of the hydrolyzed heat-alkali-treated peptide revealed partial racemization particularly at the 4(methionine) and 7(phenylalanine) positions. [Nle4]-alpha-MSH, a synthetic analogue of alpha-MSH, reversibly darkens frog skins and also exhibits prolonged activity after heat-alkali treatment. Synthesis of [Nle4, D-Phe7]-alpha-MSH provided an analogue with prolonged biological activity identical to that observed with heat-alkali-treated alpha-MSH or [Nle4]-alpha-MSH. [Nle4, D-Phe7]-alpha-MSH was resistant to enzymatic degradation by serum enzymes. In addition, this peptide exhibited dramatically increased biological activity as determined by frog skin bioassay, activation of mouse melanoma adenylate cyclase, and stimulation of mouse melanoma cell tyrosinase activity. This Nle4, D-Phe7 synthetic analogue of alpha-MSH is a very porent melanotropin, 26 times as potent as alpha-MSH in the adenylate cyclase assay. The resistance of the peptide to enzymatic degradation and its extraordinarily potent and prolonged biological activity should make this analogue of alpha-MSH an important molecular probe for studying the melanotropin receptors of both normal and abnormal (melanoma) melanocytes.
559 citations
TL;DR: The regulatory component (G/F) of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] from rabbit liver plasma membranes has been purified essentially to homogeneity.
Abstract: The regulatory component (G/F) of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] from rabbit liver plasma membranes has been purified essentially to homogeneity. The purification was accomplished by three chromatographic procedures in sodium cholate-containing solutions, followed by three steps in Lubrol-containing solutions. The specific activity of G/F was enriched 2000-fold from extracts of membranes to 3-4 mumol x min-1 x mg-1 (reconstituted adenylate cyclase activity). Purified G/F reconstitutes guanine nucleotide-, fluoride-, and hormone-stimulated adenylate cyclase activity in the adenylate cyclase-deficient variant of S49 murine lymphoma cells. G/F also recouples hormonal stimulation of the enzyme in the uncoupled variant of S49. Preparations of pure G/F contain three polypeptides with approximate molecular weights of 52,000, 45,000, and 35,000. The active G/F protein behaves as a multisubunit complex of these polypeptides. Treatment of G/F with [32P]NAD+ and cholera toxin covalently labels the molecular weight 52,000 and 45,000 polypeptides with 32P.
461 citations
325 citations
TL;DR: It is suggested that alpha1 receptors mediate those metabolic effects of alpha catecholamines which involve phosphatidylinositol turnover and the release of bound intracellular Ca2+ as well as the entry of extracellular Ca1+ in rats, hamster adipocytes and blowfly salivary glands.
293 citations
TL;DR: The adenylate cyclase of Bordetella pertussis is stimulated 100- to 1000-fold in a dose-dependent manner by calf brain calmodulin, an example of a (eukaryotic)Calmodulin effect in a prokaryote.
Abstract: The adenylate cyclase of Bordetella pertussis is stimulated 100- to 1000-fold in a dose-dependent manner by calf brain calmodulin. The system has the following properties. (i) The activation is prevented by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and restored by Ca2+. (ii) Oxidation of the methionine residues of calmodulin abolishes the ability to activate the cyclase. (iii) Trifluoperazine inhibits calmodulin-activated cyclase. (iv) A troponin C preparation stimulates the B. pertussis cyclase with < 0.01 the potency of calmodulin. Although calmodulin has not been demonstrated in prokaryotes, this is an example of a (eukaryotic) calmodulin effect in a prokaryote.
258 citations
TL;DR: In this paper, the authors studied the protein (termed "N") in erythrocyte membranes of patients with pseudohypoparathyroidism, using assays of the protein's biochemical activity and of its susceptibility to radiolabeling in the presence of [32P]NAD and cholera toxin.
Abstract: Hormone-sensitive adenylate cyclase contains a recently discovered protein component that is required for stimulation of cyclic AMP synthesis by hormones and guanine nucleotides; the component presumably couples the membrane receptor to the cyclase. We studied this protein (termed "N") in erythrocyte membranes of patients with pseudohypoparathyroidism, using assays of the protein's biochemical activity and of its susceptibility to radiolabeling in the presence of [32P]NAD and cholera toxin. By both assays, the protein's activity was reduced by 40 to 50 per cent in erythrocytes of five of 10 patients with Type I pseudohypoparathyroidism as compared with those of normal and hypoparathyroid subjects and one patient with Type II pseudohypoparathyroidism. If activity of the N protein is reduced in other tissues, this deficiency could cause the resistance of target organs in pseudohypoparathyroidism to parathyroid hormone and other hormones that work via cyclic AMP. Erythrocytes of five patients with Type I pseudohypoparathyroidism, all in one family, showed no defect in activity of the N protein; the biochemical defect of this family remains undefined.
244 citations
TL;DR: The results suggest that alamethicin disrupts membrane barriers of sarcolemmal vesicles, giving substrates and activators access to enzymic sites in the interior of the vesicle, while preserving functional coupling of enzymes to their effectors.
232 citations
TL;DR: Data provide direct evidence for the molecular interactions promoted by agonist occupancy of beta-adrenergic receptors and it is probable that the formation of a receptor-G-protein complex is crucial for catecholamine stimulation of the adenylate cyclase enzyme and, hence, transmembrane information transfer.
Abstract: Binding of the beta-adrenergic agonist [3H]hydroxybenzylisoproterenol to the beta-adrenergic receptor of rat reticulocyte membranes results in the coupling of the receptor to the guanine nucleotide regulatory protein associated with the adenylate cyclase system. This regulatory component, referred to as the G-protein, was identified by its specific [32P]-ADP-ribosylation catalyzed by cholera toxin. Incubation of [32P]ADP-ribosylated rat reticulocyte membranes with the [3H]hydroxybenzylisoproterenol agonist prior to membrane solubilization and gel exclusion chromatography resulted in the coelution of the 42,000 Mr [32P]ADP-ribosylated G-proteins with the agonist-occupied beta-adrenergic receptors. The receptor-G-protein complex was not formed when receptors were unoccupied or occupied with antagonists at the time of solubilization. Incubation of rat reticulocyte membranes with [3H]hydroxybenzylisoproterenol in the presence of guanine nucleotides reversed or prevented the formation of this receptor-G-protein complex. These data provide direct evidence for the molecular interactions promoted by agonist occupancy of beta-adrenergic receptors. It is probable that the formation of a receptor-G-protein complex is crucial for catecholamine stimulation of the adenylate cyclase enzyme and, hence, transmembrane information transfer.
206 citations
TL;DR: Observations support the notion that antiidiotypic antibodies may constitute an "internal image" of the original antigen and may mimic its biological effects.
Abstract: Rabbit antibodies induced against alprenolol, a potent beta-adrenergic antagonist, bind to other antagonists, and, with less avidity, to catecholamine agonists. Anti-idiotypic antibodies were raised against the anti-alprenolol immunoglobulins. The anti-idiotypic antibodies specifically bind and agglutinate turkey erythrocytes; this is not observed for human agglutinate turkey erythrocytes; this is not observed for human or sheep erythrocytes, which are devoid of beta-adrenergic receptors. The anti-idiotypic antibodies compete with (--)-[3H]-dihydroalprenolol for binding on the beta-adrenergic receptors on purified turkey erythrocyte membranes. The binding to the membrane-bound receptors is prevented by preincubation of the anti-idiotypic antibodies with their immunogen, the antialprenolol immunoglobulins. The binding to the receptor is not merely passive: the anti-idiotypic antibodies stimulate basal adenylate cyclase activity [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] and enhance adenylate cyclase activation by catecholamine. These observations support the notion that antiidiotypic antibodies may constitute an "internal image" of the original antigen and may mimic its biological effects.
163 citations
TL;DR: The results suggest that the activation of phospholipase A2 in the local domain of the beta-adrenergic receptor may be involved in desensitization.
Abstract: C6 astrocytoma cells contain beta-adrenergic receptors coupled to adenylate cyclase. A 2-hr exposure to l-isoproterenol results in an 80% decrease in cyclic AMP production in response to a subsequent challenge by l-isoproterenol (desensitization). This loss in responsiveness is paralleled by a 20-30% decrease in the apparent number of beta-adrenergic receptors and by increased release of arachidonic aciid into the medium. The increased release of arachidonic acid is caused by the action of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) and corresponds to increased turnover of methylated phospholipids. Mepacrine and tetracaine, both inhibitors of this phospholipase A2, are able to block l-isoproterenol-induced desensitization of cyclic AMP production and the decrease in beta-adrenergic receptors. Mellitin and phorbol ester, two activators of phospholipase A2, when preincubated with the cells cause a decreased cyclic AMP response of the cells to l-isoproterenol. These results suggest that the activation of phospholipase A2 in the local domain of the beta-adrenergic receptor may be involved in desensitization.
TL;DR: H2‐receptors are involved in the activation of adenylate cyclase of the capillary fraction of the guinea pig cerebral cortex, and this action elicits a twofold stimulation in the accumulation of cyclic AMP in this capillary fractions.
Abstract: A fraction enriched in capillaries has been prepared from the guinea pig cerebral cortex. The purity of this fraction was checked by light- and electron-microscopic examination and by its high enrichment in alkaline phosphatase and γ-glutamyl transpeptidase. In the capillary-rich fraction, the endogenous level of histamine was 1.9%’of that measured in the initial hornogenate. The histamine-synthesizing enzyme, I-histidine decarboxylase, and the metabolizing enzyme, histamine-N-methyltransferase, were barely detectable. In addition, histamine elicits a twofold stimulation in the accumulation of cyclic AMP in this capillary fraction with an EC50 of 5 γM. Agonists and antagonists of the two types of histamine receptors (H1 and H2) were used for the characterization of the receptors mediating this action: H2-receptor agonists were able to activate the adenylate cyclase with “relative potencies” similar to that found on typical H2-receptors, and cimetidine, a specific H2-receptor antagonist, competitively inhibited the response to histamine with a K1 value reflecting its interaction with a single population of H2-receptors. On the contrary, data obtained with H1-receptor agonists and antagonists reflect their interaction with H2-receptors rather than H1-receptors. Thus H2-receptors are involved in the activation of adenylate cyclase of the capillary fraction.
TL;DR: The existence of a long lived nucleotide-sensitive agonist receptor complex in both turkey and frog erythrocyte membranes is demonstrated and qualitatively similar mechanisms of receptor adenylate cyclase coupling may be operative in these two widely studied model systems.
TL;DR: Incubation of astrocytoma cells with catecholamines results in a decrease in catechlamine-stimulated adenylate cyclase activity and a concomitant alteration in the sedimentation properties of particulate beta-adrenergic receptors.
Abstract: Incubation of astrocytoma cells with catecholamines results in a decrease in catecholamine-stimulated adenylate cyclase activity and a concomitant alteration in the sedimentation properties of particulate beta-adrenergic receptors The altered receptors exhibit agonist binding properties similar to those of receptors that are "uncoupled" from adenylate cyclase
Journal Article•
TL;DR: In this article, N6-Phenylisopropyladenosine and other analogues of adenosine are potent inhibitors of adenylate cyclase in a particulate preparation of rat cerebral cortex.
Abstract: Adenosine analogues inhibit rat cerebral cortical adenylate cyclase by a receptor-mediated GTP-dependent process. N6-Phenylisopropyladenosine and other analogues of adenosine are potent inhibitors (Ki values of 10-100 nM) of adenylate cyclase in a particulate preparation of rat cerebral cortex. The detection of such inhibitory effects is facilitated by the use of a deoxy ATP assay system. The inhibition is strictly dependent on GTP, is amplified by Na+ ions, and is antagonized by methylxanthines.
TL;DR: Although not the only events in coupled mast cell activation--secretion, there is a sequential relationship among perturbation of IgE-Fc receptors, transmembrane activation of adenylate cyclase, elevation of cytoplasmic levels of cyclic AMP, activation of cyclIC AMP-dependent protein kinase, and secretion of mast cell granules.
Abstract: The initial monophasic rise in cyclic AMP beginning 5-15 sec after bridging of rat mast cell IgE-Fc receptors precedes the secretion of granule constituents, thereby implying a causal relationship. Direct evidence for a relationship between IgE-dependent transmembrane activation of adenylate cyclase and granule secretion was provided by the capacity of purine-modified (R site active) and ribose-modified (P site active) adenosine analogs, respectively, to augment and suppress mediator release while simultaneously increasing and decreasing the activity of adenylate cyclase. R site stimulation alone does not cause granule secretion but augments the rate and magnitude of IgE-Fc receptor-induced secretion, reflecting the coupled relationship of such receptors. Inhibition of adenylate cyclase at the P site attenuates the rise in cellular cyclic AMP and suppresses IgE-dependent mediator release in a parallel and superimposable dose-response fashion. Further, the relationship between the attenuation in the rise in cyclic AMP and the diminution in immunologic mediator release is linear with the regression line passing through the origin, indicating a direct relationship between the IgE-dependent activation of adenylate cyclase and preformed mediator release. Although not the only events in coupled mast cell activation--secretion, there is a sequential relationship among perturbation of IgE-Fc receptors, transmembrane activation of adenylate cyclase, elevation of cytoplasmic levels of cyclic AMP, activation of cyclic AMP-dependent protein kinase, and secretion of mast cell granules.
TL;DR: It is concluded that the guanine nucleotide regulatory protein is necessary for fluoride activation of adenylate cyclase and that the nature of the Guanineucleotide bound at the regulatory site influences fluoride stimulation.
TL;DR: The substrate for cholera toxin is a complex of the GTP-binding protein with GTP, in some way modified by a macromolecule of the cytosol that regulates adenylate cyclase activity, and the conditions for preactivation resemble those for the specific binding of Gpp(NH)p to the regulatory component of adenyate cycl enzyme.
TL;DR: The interactions of free divalent cation with the receptor-cyclase complex with regard to mechanism and site of action of metal ions, receptor-mediated inhibition of Mg2+ transport, and physiological function of the Mg 2+ interactions are discussed.
Abstract: While it is now well-established that guanine nucleotide is an important regulatory agent acting on the hormone receptor-adenylate cyclase complex, only recently has sufficient evidence accumulated to indicate that free divalent cation, particularly free Mg2+, is also an important modulatory ligand. This review discusses the interactions of free divalent cation with the receptor-cyclase complex with regard to mechanism and site of action of metal ions, receptor-mediated inhibition of Mg2+ transport, and physiological function of the Mg2+ interactions. Careful kinetic analyses indicate that the receptor-cyclase complex possesses specific sites for free Mg2+. The influence of Mg2+ on these sites is demonstrated by a Mg2+-induced increase in both agonist affinity for the hormone receptor and Vmax of adenylate cyclase catalytic activity, without change in Km for the MgATP2− substrate. Upon addition of guanine nucleotide, the effect of free Mg2+ on agonist affinity for the receptor is abolished. However, the coupling influence of nucleotide or of nucleotide plus hormone does not eliminate increased catalytic activity induced by Mg2+, but appears to increase the apparent affinity of free Mg2+ for its binding site(s). Data from specific mutant cell lines of the murine S49 lymphoma and from solubilization and reconstitution studies with S49 cells and turkey and frog erythrocytes indicate that both free Mg2+ and guanine nucleotide interact with the guanine nucleotide coupling protein at the cytoplasmic membrane face. The roles of Mn2+ and Ca2+ are less well-studied. Our assessment of published data suggests that neither of these cations is a major regulatory ligand of receptor-cyclase function. Ca2+ interacts weakly if at all with free Mg2+ sites, and the CaATP2− complex, while probably a nonproductive substrate, is a poor competitive inhibitor of the enzyme. Some evidence indicates that Ca2+ plus the Ca2+-dependent regulatory protein (calmodulin) has a potential modulatory role for a subclass of nervous system receptor-cyclase complexes. The significance of this interaction is not clear. Mn2+, unlike Ca2+, forms a productive substrate complex and in addition appears to interact with the free Mg2+ site(s). However, in contrast to the activation produced by free Mg2+, Mn2+ may be an inhibitory cation at the free metal site(s). However, no physiological significance of these interactions with Mn2+ is known. Further complexity has been added to the interactions of Mg2+ with the receptor-cyclase complex by this laboratory's description of hormonal inhibition of Mg2+ transport across the plasma membrane. Using mutant cell clones of the S49 lymphoma cell we have been able to show that this inhibition of Mg2+ transport is not mediated by cyclic AMP. The transport function appears to be a property of the receptor-cyclase complex itself or of a possible Mg2+ transport protein associated with the hormone receptor. The potential physiological significance of hormone-sensitive Mg2+ transport is discussed. Finally, we suggest, as a framework for future experimentation, a sequence of interactions of Mg2+, GTP and hormone with the receptor-cyclase complex that appears to account for the effect of and interactions between these regulatory ligands. Specifically, we suggest that activation of adenylate cyclase by hormone occurs via, a form of the receptor-cyclase complex induced by and absolutely requiring the presence of bound Mg2+. Furthermore, formation of this complex requires the absence of bound GTP. Subsequent interaction of this Mg+-containing complex with GTP results in activation of the cyclase catalytic component. We further suggest that reported differences in Mg2+/GTP interactions on receptor-cyclase complexes from different cell types are a function of minor differences (e.g. in ligand affinities) in the same fundamental characteristics. The mechanism of hormonal activation of the receptor-cyclase complex appears to be identical regardless of species or cell type and in all cases appears to require interaction with both free Mg2+ and guanine nucleotide. In this regard, it should be noted that the nucleotide coupling protein is more properly described as a metal/nucleotide coupling protein.
TL;DR: It is demonstrated here that insulin, at physiologically relevant concentrations, can trigger the cyclic AMP-dependent activation and phosphorylation of a low Km cyclIC AMP phosphodiesterase attached to the liver plasma membrane.
Abstract: Regulation of blood glucose levels by the liver is primarily achieved by the action of two peptide hormones, insulin and glucagon, which bind to specific receptors associated with the hepatocyte plasma membrane. Whilst the molecular action of glucagon at the level of the cell plasma membrane in activating adenylate cyclase is relatively well understood, we know little, if anything, of the molecular consequences of insulin occupying its receptor. We demonstrate here that insulin, at physiologically relevant concentrations, can trigger the cyclic AMP-dependent activation and phosphorylation of a low Km cyclic AMP phosphodiesterase attached to the liver plasma membrane. Such an effect may in part explain the ability of insulin to inhibit the increase in cellular cyclic AMP content that glucagon alone produces by activation of adenylate cyclase. Our observation that basal, intracellular cyclic AMP levels are insufficient to allow insulin to activate the cyclic AMP phosphodiesterase, yet those cyclic AMP levels achieved after exposure of the cells to glucagon are sufficient, gives a molecular rationale to Butcher and Sutherland's proposal that it is necessary to first elevate cellular cyclic AMP levels before they can be depressed by insulin.
TL;DR: It is suggested that the protein CaM-BP80 may have a role in the cerebrum at the site of neurotransmitter action and at the level of microtubular function in bovine brain.
Abstract: Bovine brain contains a heat-labile, 80,000-dalton calmodulin-binding protein (CaM-BP80) which inhibits the calmodulin-dependent activities of cyclic 3',5'-nucleotide phosphodiesterase, adenylate cyclase, and Ca2+-ATPase in vitro. CaM-BP80 is composed of two polypeptides (60,000 and 18,500 daltons) present in a 1:1 ratio. An antibody directed against CaM-BP80 was raised in rabbits, and a radioimmunoassay was developed, having a sensitivity of 60 fmol of CaM-BP80. Using the radioimmunoassay, we determined the levels of CaM-BP80 in various bovine tissues. The protein was found primarily in the brain, present in particularly high levels in the neostriatum. These results, together with immunohistochemical localization of CaM-BP80 at the postsynaptic densities and the microtubules of postsynaptic dendrites [Wood, J.G., Wallace, R., Whitaker, J., & Cheung, W.Y. (1980) J. Cell Biol. 84, 66-76], suggest that the protein may have a role in the cerebrum at the site of neurotransmitter action and at the level of microtubular function.
TL;DR: The heat-labile enterotoxin of Escherichia coli, like cholera toxin, activates adenylate cyclase by catalyzing the transfer of adenosine diphosphate-ribose from HAD+ to the guanyl nucleotide-dependent regulatory component of the cyclase.
Abstract: The heat-labile enterotoxin of Escherichia coli, like cholera toxin, activates adenylate cyclase by catalyzing the transfer of adenosine diphosphate-ribose from HAD+ (oxidized nicotinamide adenine dinucleotide) to the guanyl nucleotide-dependent regulatory component of the cyclase. A preparation of enterotoxin that had been released from E. coli following exposure to polymyxin B and then partially purified was found to contain two enzymatically active peptides, one of about 29,000 and the other of about 24,000 daltons, which correspond in molecular size to the enzymatically active subunit A and fragment A1 of cholera toxin, respectively. As with cholera toxin, the enzymatic activity of E. coli enterotoxin was elevated by incubation with sodium dodecyl sulfate to release active peptides. Treatment with dithiothreitol, however, had no effect. Dithiothreitol activates subunit A of cholera toxin by reducing an internal disulfide bond, but no corresponding bond appears to be present in the partially purified E. coli enterotoxin.
TL;DR: The following conclusions can be drawn: (i) catecholamines, in the presence of a guanine nucleotide, stimulate the exchange of bound and exogenous nucleotide; (ii) the exchange reaction is involved in both the activation of adenylate cyclase and in the reciprocal effects of hormone and guanines nucleotides on each other's binding.
TL;DR: It is shown that PMA exerts this effect by uncoupling epidermal β-receptors from adenylate cyclase, and that accumulation of cyclic AMP in response to isoprenaline injection is sharply inhibited.
Abstract: Alterations in β-adrenergic receptor number and function and in the hormonal responsiveness of adenylate cyclase have been observed in transformed cells1–3, and tumours4,5. Phorbol myristate acetate (PMA), a potent tumour promoter in mouse skin, induces a dramatic loss of epidermal responsiveness to catecholamines in vivo6,8, although basal levels of cyclic AMP are not affected7–9. In other work we have shown that PMA treatment does not alter the number or affinity of epidermal β-receptors, although accumulation of cyclic AMP in response to isoprenaline injection is sharply inhibited10. Evidence is presented here that PMA exerts this effect by uncoupling epidermal β-receptors from adenylate cyclase.
TL;DR: It is reported that adrenal corticoids can alter the sensitivity of this system to NA, and this system has provided the basis for a revised catecholamine hypothesis of affective disorders.
Abstract: Considerable evidence indicates that alterations in the availability of noradrenaline (NA) at postsynaptic sites can cause compensatory changes in the NA stimulated cyclic AMP generating system in various brain regions. Thus, an increased responsiveness to NA has been reported in the limbic forebrain and cortex following reserpine or 6-hydroxydopamine1–3. Conversely, manipulations which increase the availability of NA at receptor sites (monoamine oxidase (MAO) inhibitors, electroconvulsive treatment (ECT), tricyclic antidepressants) cause a decrease in responsiveness4–6. This up and down-regulation of central noradrenergic sensitivity is generally linked to changes of the density of β-adrenergic receptors7–10. The findings that psychotropic drugs which can either precipitate (reserpine) or alleviate (tricyclic antidepressants, MAO inhibitors and also ECT) depressive states cause opposite changes in the NA receptor-coupled adenylate cyclase system in brain have provided the basis for a revised catecholamine hypothesis of affective disorders11. It has also been suggested that the pituitary adrenal axis may have a role in mood disorders12. Since manipulation of the levels of corticosterone through bilateral adrenalectomy can alter the sensitivity of catecholamine-sensitive adenylate cyclase systems in preparations from liver13,14 and adipose tissue15, we have tried to determine if corticosterone could regulate the NA receptor-coupled adenylate cyclase system in brain tissue. We now report that adrenal corticoids can alter the sensitivity of this system to NA.
TL;DR: The results show that the re is an inverse relationship between adenylate cyclase activity and phosphodiesterases activity and suggest that intracellular calcium may mediate a coordinated regulation of the rates of synthesis and degradation of cyclic nucleotides.
TL;DR: The ciliary process epithelium was found to be enriched in an adenylate cyclase with pharmacological characteristics indicative of a predominance of beta 2-adrenergic receptors, consistent with the possibility that the adrenergic nervous system may regulate aqueous humor production through a direct effect on secretion.
Abstract: To determine the site and possible mechanism of action of adrenergic agents in regulating intraocular pressure, experiments were undertaken to identify, localize, and characterize beta-adrenergic receptors associated with adenylate cyclase in various ocular tissues involved in secretion and reabsorption of aqueous humor. The ciliary process epithelium was found to be enriched in an adenylate cyclase with pharmacological characteristics indicative of a predominance of beta 2-adrenergic receptors. The results are consistent with the possibility that the adrenergic nervous system may regulate aqueous humor production through a direct effect on secretion. The data also are relevant to the potential development of drugs that can control increased intraocular pressure.
TL;DR: The maturation of rat reticulocytes to erythrocytes is paralleled by a marked loss of adenylate cyclase responsiveness to catecholamines and guanine nucleotides without significant loss of basal enzyme activity, which suggests that one molecular concomitant of rat ERYthrocyte maturation is a decrease in the effectiveness of receptor-guanineucleotide regulatory protein communication.
TL;DR: In ghosts of hamster adipocytes, the regulation of adenylate cyclase by prostaglandins, α-adrenergic agonists and nicotinic acid was studied, suggesting that an α2 of receptors is involved in this catecholamine-induced inhibition.
Abstract: In ghosts of hamster adipocytes, the regulation of adenylate cyclase (ATP: pyrophosphate lyase, cyclizing; EC 4.6.1.1) activity by prostaglandins, α-adrenergic agonists and nicotinic acid was studied. These three classes of antilipolytic agents caused adenylate cyclase inhibition without an apparent lag phase. Maximal inhibitions observed ranged between about 45% (by α-adrenergic agonists) and 60% (by prostaglandins and nicotinic acid). The order of potency for the inhibitory prostaglandins (PG) was PGE1 ≧ PGE2>PGF2α≅PGI2>PGD2>6-keto PGF1α. The IC50 values obtained were about 0.007, 0.06, 0.3 and 1 μM for PGE1, PGF2α, PGD2 and 6-keto PGF1α, respectively. α-Adrenergic agonists, studied in the presence of the β-adrenergic blocking agent, propranolol (30 μM), inhibited the fat cell enzyme with the order of potency (1)-adrenaline > (1)-α-methylnoradrenaline ≅ (1)-noradrenaline > clonidine ≅ tetryzoline > (1)-phenylephrine. The IC50 values obtained for (1)-adrenaline and (1)-noradrenaline were about 3 and 10 μM, respectively. The inhibitory effect of (1)-adrenaline was blocked by the α-adrenergic antagonists with the potency order yohimbine ≅ phentolamine > prazosin. These findings suggest that an α2 of receptors is involved in this catecholamine-induced inhibition. Nicotinic acid (10 μM) reduced adenylate cyclase activity by about 60% with half-maximal effectiveness at about 0.6 μM. The nicotinic acid derivatives, nicotinamide, β-pyridylcarbinol and NAD (up to 100 μM), had no effect on enzyme activity.
TL;DR: The 5-HT receptor linked to adenylate cyclase and the high affinity binding site for [3H]-5-HT were compared on the basis of their kinetic and pharmacological properties in the CNS of new born rats to provide evidence for the possible existence of multiple receptors for 5- HT in the rat brain.