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:3.5.4.4 (adenosine deaminase)
5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Analysis of cyclic nucleotide phosphodiesterase (PDE) activity in cellular fractions from cultured rat pheochromocytoma (PC12) cells has shown that the predominant hydrolytic activity in both cytosolic and particulate compartments is characteristic of a PDE II, the cGMP-activatable family of PDE isozymes. Cytosolic PDE activity was purified to a high degree utilizing DE-52 anion exchange and cGMP-Sepharose affinity chromatographies. The physicochemical properties of PC12 PDE II were similar to those of PDE II isolated from particulate or soluble fractions of other tissues, including subunit molecular weight of approximately 102,000, activation of cAMP hydrolysis by cGMP, and positive cooperative kinetic behavior for cAMP and cGMP hydrolysis. The potential role of PDE II in regulating cAMP metabolism in intact PC12 cells was studied using an [3H]adenine prelabeling technique. Stimulation of PC12 cell adenosine receptors resulted in a 5-8-fold increase in cAMP accumulation. Removal of the adenosine stimulus by the addition of exogenous adenosine deaminase resulted in a rapid decay of cAMP to prestimulated basal levels within 2 min. Treatment of PC12 cells with atrial natriuretic factor or sodium nitroprusside caused 1) increased intracellular cGMP levels, 2) attenuation of adenosine-stimulated cAMP accumulation, and 3) increased rates of cAMP decay after removal of the adenosine stimulus. Treatment of PC12 cells with HL-725 (a potent inhibitor of isolated PDE II activity in vitro) caused 1) increased basal cAMP accumulation, 2) potentiation of adenosine-stimulated cAMP accumulation, and 3) retardation of the rate of cAMP decay after removal of the adenosine stimulus. HL-725 blocked both the attenuation of cAMP accumulation and the accelerated rate of cAMP decay observed with the cGMP-elevating agents. These results suggest that, in PC12 cells, drugs or hormones that inhibit PDE II or increase intracellular cGMP levels to activate PDE II can modulate cAMP metabolism by altering the catalytic status of the enzyme.
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PMID:Phosphodiesterase II, the cGMP-activatable cyclic nucleotide phosphodiesterase, regulates cyclic AMP metabolism in PC12 cells. 164 46

Adenosine increases the activity of tyrosine 3-monooxygenase in intact pheochromocytoma cells. The effect of adenosine is not dependent upon extracellular Ca2+, and is not accompanied by an increase in catecholamine secretion from the cells. Adenosine deaminase decreases the basal activity of tyrosine 3-monooxygenase, and almost completely abolishes the activation of this enzyme by adenosine. In cells treated with adenosine deaminase, 2-chloroadenosine causes a 2- to 5-fold increase in tyrosine 3-monooxygenase activity. 2-Chloroadenosine produces half-maximal activation at a concentration of 0.1 microM, and maximal activation at 10 microM. Incubation of cells with 2-chloroadenosine produces a stable activation of tyrosine 3-monooxygenase, as measured in vitro. Finally, 3-chloroadenosine increases the content of cAMP in pheochromocytoma cells, and increases the incorporation of 3H into cAMP in cells that have been preincubated with [3H]adenine. This rise in cAMP presumably mediates the activation of tyrosine 3-monooxygenase by 2-chloroadenosine. Adenosine appears to be an endogenous regulator of tyrosine 3-monooxygenase activity in pheochromocytoma cells.
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PMID:Activation of tyrosine 3-monooxygenase in pheochromocytoma cells by adenosine. 610 63

The decrease in receptor-stimulated cyclic AMP production after chronic ethanol exposure was suggested previously to be secondary to an ethanol-induced increase in extracellular adenosine. The present study was undertaken to ascertain whether a similar mechanism was responsible for the ethanol-induced desensitization of cyclic AMP production in PC12 pheochromocytoma cells. The acute addition of ethanol in vitro significantly increased both basal cyclic AMP content and extracellular levels of adenosine. A 4-day exposure to ethanol decreased basal as well as 2-chloroadenosine- and forskolin-stimulated cyclic AMP contents. No change in cyclic AMP content was observed after a 2-day exposure of PC12 cells to ethanol. Inclusion of adenosine deaminase during the chronic ethanol treatment significantly decreased extracellular levels of adenosine, yet the percentage decrease in 2-chloroadenosine- and forskolin-stimulated cyclic AMP levels after chronic ethanol exposure was not changed by the inclusion of the adenosine deaminase. Similar results were obtained when the chronic treatment was carried out with serum-free defined media. The ethanol-induced desensitization could not be mimicked by chronic exposure of PC12 cells to adenosine analogues. A 24-h exposure of PC12 cells to 2-chloroadenosine resulted in a decrease in the subsequent ability of this adenosine analogue to stimulate cyclic AMP content, but basal and forskolin-stimulated cyclic AMP levels were increased. Similar results were obtained after a 4-day exposure of PC12 cells to 2-chloroadenosine or 5'-N-ethylcarboxamido-adenosine. The present results indicate that the ethanol-induced decrease in receptor-stimulated cyclic AMP content in PC12 cells is not due to an increase in extracellular adenosine.
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PMID:Role of extracellular adenosine in ethanol-induced desensitization of cyclic AMP production. 838 60

PC12 pheochromocytoma cells have P2 purinoceptors which are activated by ATP and coupled to Ca2+ influx and catecholamine release. Also PC12 cells have adenosine receptors coupled positively to adenylyl cyclase, and cyclic AMP regulates cell functions such as catecholamine release. The effects of ATP and ATP analogs on cyclic AMP accumulation in PC12 cells were investigated in this study. ATP and adenosine 5'-0-(3-thiotriphosphate) stimulated cyclic AMP accumulation at low concentrations up to 300 microM but showed inhibitory effects above this concentration. 2',3'-O-(4-Benzoyl)benzoyl ATP and 2-methylthio ATP showed similar effects, although the responses were very limited. Addition of adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) or beta, gamma-methylene ATP, but not alpha, beta-methylene ATP, stimulated cyclic AMP accumulation markedly without causing an inhibitory phase. The effects of ATP, ADP beta S and beta, gamma-methylene ATP were not inhibited by adenosine deaminase or specific antagonists to A1 and A2 adenosine receptors. Neither ADp beta S nor beta, gamma-methylene ATP showed any effect on Ca2+ influx or noradrenaline release. Suramin, a P2 receptors antagonists, had no inhibitory effect against ATP analog-stimulated cyclic AMP accumulation, although reactive blue 2 inhibited the beta, gamma-methylene ATP-stimulated reaction but not that up-regulated by ADP beta S. These findings suggest that the pharmacological characteristics of these ATP receptors coupled to adenylyl cyclase are clearly different from those of ligand-gated ion channels defined by P2X purinoceptors, which have been cloned and shown to be coupled to Ca2+ influx and catecholamine release in PC12 cells. The existence of a new type of P2 purinoceptor-mediating stimulation of adenylyl cyclase is proposed in PC12 cells.
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PMID:P2 purinoceptor-mediated stimulation of adenylyl cyclase in PC12 cells. 895 42

In addition to their well known roles within cells, purine nucleotides such as adenosine 5' triphosphate (ATP) and guanosine 5' triphosphate (GTP), nucleosides such as adenosine and guanosine and bases, such as adenine and guanine and their metabolic products xanthine and hypoxanthine are released into the extracellular space where they act as intercellular signaling molecules. In the nervous system they mediate both immediate effects, such as neurotransmission, and trophic effects which induce changes in cell metabolism, structure and function and therefore have a longer time course. Some trophic effects of purines are mediated via purinergic cell surface receptors, whereas others require uptake of purines by the target cells. Purine nucleosides and nucleotides, especially guanosine, ATP and GTP stimulate incorporation of [3H]thymidine into DNA of astrocytes and microglia and concomitant mitosis in vitro. High concentrations of adenosine also induce apoptosis, through both activation of cell-surface A3 receptors and through a mechanism requiring uptake into the cells. Extracellular purines also stimulate the synthesis and release of protein trophic factors by astrocytes, including bFGF (basic fibroblast growth factor), nerve growth factor (NGF), neurotrophin-3, ciliary neurotrophic factor and S-100beta protein. In vivo infusion into brain of adenosine analogs stimulates reactive gliosis. Purine nucleosides and nucleotides also stimulate the differentiation and process outgrowth from various neurons including primary cultures of hippocampal neurons and pheochromocytoma cells. A tonic release of ATP from neurons, its hydrolysis by ecto-nucleotidases and subsequent re-uptake by axons appears crucial for normal axonal growth. Guanosine and GTP, through apparently different mechanisms, are also potent stimulators of axonal growth in vitro. In vivo the extracellular concentration of purines depends on a balance between the release of purines from cells and their re-uptake and extracellular metabolism. Purine nucleosides and nucleotides are released from neurons by exocytosis and from both neurons and glia by non-exocytotic mechanisms. Nucleosides are principally released through the equilibratory nucleoside transmembrane transporters whereas nucleotides may be transported through the ATP binding cassette family of proteins, including the multidrug resistance protein. The extracellular purine nucleotides are rapidly metabolized by ectonucleotidases. Adenosine is deaminated by adenosine deaminase (ADA) and guanosine is converted to guanine and deaminated by guanase. Nucleosides are also removed from the extracellular space into neurons and glia by transporter systems. Large quantities of purines, particularly guanosine and, to a lesser extent adenosine, are released extracellularly following ischemia or trauma. Thus purines are likely to exert trophic effects in vivo following trauma. The extracellular purine nucleotide GTP enhances the tonic release of adenine nucleotides, whereas the nucleoside guanosine stimulates tonic release of adenosine and its metabolic products. The trophic effects of guanosine and GTP may depend on this process. Guanosine is likely to be an important trophic effector in vivo because high concentrations remain extracellularly for up to a week after focal brain injury. Purine derivatives are now in clinical trials in humans as memory-enhancing agents in Alzheimer's disease. Two of these, propentofylline and AIT-082, are trophic effectors in animals, increasing production of neurotrophic factors in brain and spinal cord. Likely more clinical uses for purine derivatives will be found; purines interact at the level of signal-transduction pathways with other transmitters, for example, glutamate. They can beneficially modify the actions of these other transmitters.
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PMID:Trophic effects of purines in neurons and glial cells. 1084 57

The effects of cilostazol, a dual inhibitor of type 3 phosphodiesterase and adenosine uptake, on ion currents were investigated in pituitary GH(3) cells and pheochromocytoma PC12 cells. In whole-cell configuration, cilostazol (10 microm) reversibly increased the amplitude of Ca(2+)-activated K(+) current [I(K(Ca))]. Cilostazol-induced increase in I(K(Ca)) was suppressed by paxilline (1 microM) but not glibenclamide (10 microm), dequalinium dichloride (10 microM), or beta-bungarotoxin (200 nM). Pretreatment of adenosine deaminase (1 U/ml) or alpha,beta-methylene-ADP (100 microM) for 5 h did not alter the magnitude of cilostazol-stimulated I(K(Ca)). Cilostazol (30 microM) slightly suppressed voltage-dependent l-type Ca(2+) current. In inside-out configuration, bath application of cilostazol (10 microM) into intracellular surface caused no change in single-channel conductance; however, it did increase the activity of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. Cilostazol enhanced the channel activity in a concentration-dependent manner with an EC(50) value of 3.5 microM. Cilostazol (10 microM) shifted the activation curve of BK(Ca) channels to less positive membrane potentials. Changes in the kinetic behavior of BK(Ca) channels caused by cilostazol were related to an increase in mean open time and a decrease in mean closed time. Under current-clamp configuration, cilostazol decreased the firing frequency of action potentials. In pheochromocytoma PC12 cells, cilostazol (10 microM) also increased BK(Ca) channel activity. Cilostazol-mediated stimulation of I(K(Ca)) appeared to be not linked to its inhibition of adenosine uptake or phosphodiesterase. The channel-stimulating properties of cilostazol may, at least in part, contribute to the underlying mechanisms by which it affects neuroendocrine function.
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PMID:Cilostazol, an inhibitor of type 3 phosphodiesterase, stimulates large-conductance, calcium-activated potassium channels in pituitary GH3 cells and pheochromocytoma PC12 cells. 1464 20

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