Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adenosine (ADO) has a pharmacological profile which makes it an interesting 'drug' to handle many of the problems arising with ischemia and reperfusion. In human blood, however, it is rapidly taken up by the red blood cells and metabolized to inactive inosine and hypoxanthine. This transporter-mediated uptake can be specifically inhibited in vitro by a few drugs, known as nucleoside transport inhibitors. It has been reported that ADO can inhibit platelet aggregation in whole blood in the presence of dipyridamole, and it is well-known that ADO can inhibit the respiratory burst of purified neutrophils induced by certain stimuli. We investigated the effect of some of these drugs on the ADO-mediated inhibition of the fMLP-induced respiratory burst in neutrophils (as measured by lucigenin-enhanced luminescence), in undiluted whole blood. The combination of R 75,231 (a newly developed analog of mioflazine, with unique pharmacokinetic properties, for details see with ADO (0.1 microM) inhibited the luminescence by 40 +/- 4% (n = 10), while either R 75,231 or ADO alone did not affect the response to fMLP. In the presence of ADO (1 microM), R 75,231 (EC50 = 1.9 +/- 0.3 x 10(-7) M) (n = 3) was almost as potent as dilazep (EC50 = 1.1 +/- 0.2 x 10(-7) M) (n = 3), but far more potent than dipyridamole (EC50 = 1.2 +/- 0.2 x 10(-6) M) (n = 3). The present data show that ADO can inhibit PMN-activation in whole blood in the presence of R 75,231 or of other nucleoside transport inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)
J Mol Cell Cardiol 1991 Jul
PMID:Nucleoside transport inhibition and fMLP-stimulated whole blood luminescence. 179 29

P2Y-Purinergic receptors were solubilized from turkey erythrocyte plasma membranes with the nonionic detergent digitonin. Adenosine 5'-O-(2-[35S]thiodiphosphate) ([35S]ADP beta S) labeled a single population of soluble high affinity sites (Kd = 12.9 nM; Bmax = 4.5 pmol/mg of protein) in an equilibrium binding assay; adenine nucleotide analogs competitively inhibited [35S]ADP beta S binding with a rank order of potency consistent with that for P2Y-purinergic receptors. Radioligand binding to solubilized P2Y-purinergic receptors was noncompetitively inhibited by guanine nucleotides with a rank order of potency that was in agreement with the potency order observed for guanine nucleotide-mediated inhibition of [35S]ADP beta S binding in purified turkey erythrocyte plasma membranes. The rate constant for dissociation of [35S]ADP beta S from solubilized receptors was increased 2.3-fold by guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). Plasma membrane P2Y-purinergic receptors were labeled with [35S]ADP beta S or covalently labeled with the photoaffinity probe 3'-O-(4-benzoyl)benzoyl adenosine 5'-[alpha-32P]triphosphate ([alpha-32P]BzATP) before solubilization and gel filtration chromatography on Superose 12. [35S]ADP beta S- or [alpha-32P]BzATP-labeled species eluted as a single peak of radioactivity of apparent Mr greater than or equal to 300,000. Incubation of the Mr greater than or equal to 300,000 protein species with GTP gamma S before rechromatography resulted in loss of labeling of proteins by [35S]ADP beta S and a shift in apparent size of the covalently [alpha-32P]BzATP-labeled species to a single peak of radioactivity of approximate Mr 70,000. These results suggest that a P2Y-purinergic receptor-guanine nucleotide regulatory protein complex is stable to membrane solubilization with digitonin, even in the absence of prebound agonist.
Mol Pharmacol 1991 Jul
PMID:Solubilization of a guanine nucleotide-sensitive form of the P2Y-purinergic receptor. 190 78

The triazoloquinazoline CGS 15943 is the first reported nonxanthine adenosine antagonist that has high affinity for brain adenosine receptors. In the present study, the binding of [3H] CGS 15943 to recognition sites in rat cortical membranes was characterized. Saturation experiments revealed that [3H]CGS 15943 labeled a single class of recognition sites with high affinity (Kd = 4 nM) and limited capacity (Bmax = 1.5 pmol/mg of protein). Competition studies revealed that the binding of [3H]CGS 15943 was consistent with the labeling of brain adenosine A1 receptors. Adenosine agonists inhibited 1 nM [3H]CGS 15943 binding with the following order of activity N6-cyclopentyladenosine (IC50 = 15 nM) greater than 2-chloroadenosine greater than (R)-N6-phenylisopropyladenosine greater than 5'-N6-ethylcarboxamidoadenosine greater than (S)N6-phenylisopropyladenosine greater than CGS 21680 greater than CV 1808 (IC50 greater than 10,000 nM). The potency order for adenosine antagonists was CGS 15943 (IC50 = 5 nM) greater than 8-phenyltheophylline greater than 1,3-dipropyl-8-(4-amino-2-chloro)phenylxanthine greater than 1,3-diethyl-8-phenylxanthine greater than theophylline = caffeine (IC50 greater than 10,000 nM). Antagonist inhibition curves were steep and best described by a one-site binding model. In contrast, adenosine A1 agonist competition curves were shallow, as indicated by Hill coefficients less than unity. Computer analysis revealed that these inhibition curves were best described by a two-site binding model. Agonist competition curves generated in the presence of 1 mM GTP resulted in a rightward shift and steepening of the inhibition-concentration curves, whereas antagonist binding was not altered in the presence of GTP. The complex binding interactions found with adenosine agonists indicate that [3H]CGS 15943 labels both high and low affinity components of the adenosine A1 receptor in the rat cortex. Additionally, the present data also provide some evidence that [3H]CGS 15943 may also recognize an additional low affinity binding component, which may represent a putative low affinity A2b receptor in this tissue.
Mol Pharmacol 1991 Jan
PMID:Characterization of the binding of a novel nonxanthine adenosine antagonist radioligand, [3H]CGS 15943, to multiple affinity states of the adenosine A1 receptor in the rat cortex. 198 52

Kinetic analysis of the binding of [3H]nitrobenzylthioinosine ([3H] NBMPR) to Ehrlich ascites tumor cell plasma membranes was conducted in the presence and absence of a variety of nucleoside transport inhibitors and substrates. The association of [3H] NBMPR with Ehrlich cell membranes occurred in two distinct phases, possibly reflecting functional conformation changes in the [3H]NBMPR binding site/nucleoside transporter complex. Inhibitors of the equilibrium binding of [3H]NBMPR, tested at submaximal inhibitory concentrations, generally decreased the rate of association of [3H]NBMPR, but the magnitude of this effect varied significantly with the agent tested. Adenosine and diazepam had relatively minor effects on the association rate, whereas dipyridamole and mioflazine slowed the rate dramatically. Inhibitors of nucleoside transport also decreased the rate of dissociation of [3H]NBMPR, with an order of potency significantly different from their relative potencies as inhibitors of the equilibrium binding of [3H]NBMPR. Dilazep, dipyridamole, and mioflazine were effective inhibitors of both [3H]NBMPR dissociation and equilibrium binding. The lidoflazine analogue R75231, on the other hand, had no effect on the rate of dissociation of [3H]NBMPR at concentrations below 300 microM, even though it was one of the most potent inhibitors of [3H]NBMPR binding tested (Ki less than 100 nM). In contrast, a series of natural substrates for the nucleoside transport system enhanced the rate of dissociation of [3H]NBMPR with an order of effectiveness that paralleled their relative affinities for the permeant site of the transporter. The most effective enhancers of [3H]NBMPR dissociation, however, were the benzodiazepines diazepam, chlordiazepoxide, and triazolam. Comparable effects of adenosine and dipyridamole on [3H]NBMPR dissociation rate were obtained upon solubilization of the membranes with octylglucoside, suggesting that this phenomenon was not due to changes in membrane fluidity. These results are compatible with the existence of specific ligand recognition sites on the nucleoside transport complex of Ehrlich cells that are pharmacologically distinct from, but allosterically linked to, the high affinity binding sites for [3H]NBMPR. The marked effects on [3H]NBMPR binding kinetics that result from ligand interactions with these sites must be considered in the design and analysis of all studies involving the use of [3H]NBMPR as a high affinity probe for the nucleoside transport system.
Mol Pharmacol 1991 Jun
PMID:Kinetic analysis of ligand binding to the Ehrlich cell nucleoside transporter: pharmacological characterization of allosteric interactions with the [3H]nitrobenzylthioinosine binding site. 205 91

A background current induced by isoprenaline, and its modulation by adenosine and ATP, have been studied using the whole cell patch clamp technique in guinea-pig ventricular myocytes. Isoprenaline (1-2000 nM) caused an inward shift of the holding current, in addition to increasing the inward calcium current (ICa). The effect on the background current was maximal earlier than the increase in ICa, but was of shorter duration. The magnitude of the background current was concentration dependent with a EC50 of 8 nM. This current was unaffected by tetrodotoxin 20 microM, Cd 200 microM or verapamil, 10 microM and potassium channel blockade (intracellular Cs, extracellular Cs 20 mM, Ba 2 mM or tetraethylammonium 10 mM). Lowering the chloride content of the electrode solution reduced the magnitude of the background current. The background current was also induced by histamine (1 or 10 microM). Adenosine (10-1000 microM) and and ATP (200 microM) antagonised the isoprenaline induced background current and the increase in ICa. The histamine effects on these currents were also reduced by adenosine. These results suggest that this background current may be carried by chloride ions and may be mediated via an increase in intracellular cyclic AMP concentration. Antagonism of this current may contribute to the antiarrhythmic actions of adenosine and ATP but their mechanisms of action are yet to be determined.
J Mol Cell Cardiol 1990 Dec
PMID:Antagonism by adenosine and ATP of an isoprenaline-induced background current in guinea-pig ventricular myocytes. 208 55

Because adenosine narrows asthmatic airways, is released during hypoxia and by mast cells, and is antagonized by theophylline, it may play a role in asthma. I characterized the first step in pulmonary responses to adenosine: its adenosine receptor. Plasma membranes, prepared from macroscopically normal human peripheral lung, were incubated with 10 nM 5'-N-ethylcarboxamido[3H]adenosine ([3H]NECA) and various concentrations of competing ligand under experimentally determined optimal conditions: 4 degrees C, pH 7.4, 5 mM MgCl2, 1.8 mg protein/ml, 30-min incubation time. Bound and free ligand were separated by rapid vacuum filtration, and the radioactive counts were analyzed using a weighted, non-linear, least-squares curve-fitting program, LIGAND. Analyzed together, the data from the lungs of 6 patients revealed a single binding site with a dissociation constant (Kd) for NECA of 200 nM +/- 14% and a receptor concentration of 543 fmol/mg protein +/- 13%. Analyzed separately, the individual Kds ranged from 133 to 430 nM and the receptor concentrations from 338 to 811 fmol/mg protein. Adenosine receptor ligands competed with NECA in an A2 rank order of potency: NECA greater than 8-phenyltheophylline greater than 3-isobutyl-1-methylxanthine greater than theophylline greater than N6-L-phenylisopropyladenosine greater than N6-D-phenylisopropyladenosine greater than N6-cyclohexyladenosine. Theophylline bound to the receptor with an inhibition constant (Ki = 70.9 microM +/- 28%) near the therapeutic range (28 to 56 microM). Cromolyn also bound with high affinity (Ki = 5.42 microM +/- 47%). I conclude that human lung adenosine receptors: (1) are single-site receptors, probably of the A2 subtype and (2) bind to both theophylline and cromolyn.
Am J Respir Cell Mol Biol 1990 Feb
PMID:Characterization of the human peripheral lung adenosine receptor. 240 76

Adenosine receptors in the smooth muscle cell line DDT1 MF-2 were studied by radioligand binding using the A1 receptor-selective antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine [( 3H]DPCPX) as the ligand. Binding characteristics were similar in intact cells and in membranes (KD value of approximately 1 nM). The maximum binding amounted to 183 fmol/10(6) intact cells or 344 fmol/mg of membranes. To characterize the receptor, competition experiments were performed by inhibiting [3H]DPCPX binding with several adenosine agonists and antagonists. Adenosine receptor antagonists appeared to bind to a single class of binding site, both in membranes and intact cells. The order of potency was DPCPX = CGS 15943A greater than 8-cyclopentyl-1,3-dimethylxanthine greater than 8-(p-sulfophenyl)-theophylline greater than 3-isobutyl-1-methylxanthine greater than theophylline. Competition curves with adenosine agonists in membranes were best described by a two-site rather than a one-site model. At equilibrium in intact cells, only a single site was detected at both 4 degrees and 25 degrees. However, short term incubations (1-4 min) at 25 degrees showed biphasic binding curves in intact cells. The equilibrium KD values for intact cells were similar to the low affinity KD values in membranes (KL). The order of potency was N6-cyclopentyladenosine greater than or equal to (-)-(R)-N6-phenylisopropyladenosine[(R)-PIA] greater than or equal to N6-cyclohexyl adenosine greater than 5'-N-ethylcarboxamidoadenosine (NECA) greater than 2-chloroadenosine greater than adenosine (intact cells only) greater than 2-phenylaminoadenosine (CV 1808). Treatment of cells with pertussis toxin ADP-ribosylated GTP-binding proteins and eliminated the high affinity agonist binding in membranes but did not affect binding to intact cells. The addition of GTP (100 microM) also shifted the competition curves from bi- to monophasic curves in membranes. Adenosine receptor agonists inhibited the formation of cAMP induced by isoprenaline (IC50 for (R)-PIA, 0.4 nM). This inhibition could be prevented with adenosine receptor antagonists. Pretreatment with pertussis toxin also reversed these effects and actually revealed functional A2 receptors, as shown by the formation of cAMP induced by NECA. In conclusion, the equilibrium binding of A1 receptor agonists to intact smooth muscle cells is similar to the low affinity binding observed in membranes. In addition, it is suggested that agonists may transiently convert the A1 receptor from a "resting" low affinity state to a high affinity state coupled to a GTP-binding protein.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Pharmacol 1990 Nov
PMID:Characterization of adenosine A1 receptors in intact DDT1 MF-2 smooth muscle cells. 217 73

Several 2-amino-3-benzoylthiophenes were found to increase the binding of [3H]N6-cyclohexyladenosine to A1 adenosine receptors in rat brain membranes. Concentration-response curves were bell-shaped, with up to 45% stimulation of binding at 10 microM followed by inhibition at higher concentrations. Because these compounds originated from a series of nonxanthine adenosine antagonists, the inhibition of binding was attributed to the presence of interfering adenosine antagonist activity. The compounds stimulated binding of several A1 agonist ligands but only inhibited binding of the A1 antagonist ligand [3H]8-cyclopentyl-1,3-dipropylxanthine, indicating that enhancement was specific for the agonist conformation of the receptor. The enhancement was also specific for the A1 receptor, because agonist binding to A2 adenosine, M2 muscarinic, alpha 2 adrenergic, and delta opiate receptors showed little or no enhancement. Uncoupling of the A1 receptor from the inhibitory guanine nucleotide-binding protein did not prevent enhancement. The enhancers slowed the dissociation of [3H]N6-cyclohexyladenosine from the A1 receptor, implying an allosteric mechanism of action. The inhibition of forskolin-stimulated cyclic AMP accumulation in FRTL-5 cells was employed as a functional index of A1 receptor activation. The enhancers caused up to 19-fold leftward shifts in the concentration-response curve for N6-cyclopentyladenosine and also caused up to 55% inhibition of cyclic AMP accumulation in the absence of agonist. The binding and functional results are consistent with a model in which the enhancers bind preferentially to the agonist conformation of the A1 receptor, thereby shifting the receptor equilibrium in favor of agonist binding. Adenosine enhancers may be useful for ischemia and other conditions involving local energy deficits. More generally, allosteric enhancers may provide a means for strengthening physiological control circuits in a variety of receptor systems.
Mol Pharmacol 1990 Dec
PMID:Allosteric enhancement of adenosine A1 receptor binding and function by 2-amino-3-benzoylthiophenes. 217 10

Antibodies against adenosine markedly inhibited in vitro transcription in isolated BHK 21 nuclei in a dose-dependent manner. The inhibition was specific as it could be completely reversed by the addition of homologous hapten. Addition of RNA at low concentration reversed the inhibition, whereas excess DNA did not have any effect. Adenosine antibodies also inhibited in vitro transcription with calf thymus DNA and E. coli RNA polymerase. Antibodies that react with DNA but not with RNA such as anti-dpA, anti-dpC and anti-DNA failed to inhibit in vitro transcription in isolated nuclei as well as with calf thymus DNA and E. coli RNA polymerase. The results strongly indicate that the binding of adenosine antibodies to RNA is responsible for the inhibition of transcription.
Mol Immunol 1990 Nov
PMID:Inhibition of in vitro transcription by adenosine antibodies. 224 89

Adenosine agonists have now been shown by several laboratories to have profound neuroprotective effects when administered either pre- or postischemia. In an effort to determine whether these effects are centrally mediated, the effects of the non-brain-permeable adenosine receptor antagonist 8-sulfophenyl-theophylline (8-SPTH) on cyclohexyladenosine (CHA) -mediated protection was determined. Both survival and neurologic outcome were assessed in gerbils following 30 minutes of bilateral carotid occlusion. A dose of 2 mg/kg of CHA 5 minutes postreperfusion resulted in highly significant increases in survival relative to saline injected controls. Administration of doses of 8-SPTH sufficient to normalize the hypotension observed with CHA resulted in the same degree of postischemic protection. Similar results were obtained when neurologic status was evaluated. The results indicate that the neuroprotective effects of CHA are apparently centrally mediated.
J Mol Neurosci 1990
PMID:Cerebral ischemia in gerbils: postischemic administration of cyclohexyl adenosine and 8-sulfophenyl-theophylline. 225


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