共查询到20条相似文献,搜索用时 15 毫秒
1.
Martin J. Lohse Dieter Ukena Ulrich Schwabe 《Naunyn-Schmiedeberg's archives of pharmacology》1985,328(3):310-316
Summary Adenosine has been shown to have negative inotropic, chronotropic and dromotropic effects on the heart. The pharmacological profiles of these effects suggest that they are mediated via Ri (A1) adenosine receptors, but a direct demonstration of these receptors is still missing. In the present study we report direct labelling of these receptors with (-)N6-[125I]-p-hydroxyphenylisopropyladenosine ([125I]HPIA). The radioligand bound in a saturable and reversible manner to a crude membrane preparation, the B
max-value was 30.5 fmol/mg protein and the K
D-value 1.1 nmol/l. A similar affinity of the ligand was obtained in kinetic and competition experiments. Competition experiments with a variety of adenosine analogues gave a pharmacological profile characteristic of Ri adenosine receptors with high affinities of N6-substituted derivatives and a marked stereospecificity for N6-phenylisopropyladenosine (PIA). Purification of the membrane preparation by density gradient centrifugation resulted in a 30-fold increase in the number of binding sites which was paralleled by a similar increase in the number of binding sites for [3H]ouabain. Guanine nucleotides decreased binding of [125I]HPIA in a dose-dependent manner, but the IC50-values were considerably higher than those reported in other tissues. Finally, binding of [125I]HPIA appeared to be entropy-driven which has been shown to be characteristic of agonist binding to Ri adenosine receptors. These results suggest the presence of Ri adenosine receptors in ventricular myocardium which may be responsible for the mediation of the effects of adenosine and its analogues.Abbreviations [125I]HPIA
(-)N6-[125I]-p-hydroxyphenylisopropyladenosine
- (-)IHPIA
(-)N6-iodo-p-hydroxyphenylisopropyladenosine
- (+)/(-)PIA
(+)/(-)N6-phenylisopropyladenosine
- CHA
N6-cyclohexyladenosine
- NECA
5-N-ethylcarboxamidoadenosine
- App(NH)p
5-adenylylimidodiphosphate
- Gpp(NH)p
5-guanylylimidodiphosphate 相似文献
2.
Michael Williams Albert Braunwalder Thomas J. Erickson 《Naunyn-Schmiedeberg's archives of pharmacology》1986,332(2):179-183
Summary The binding of [3H]-Cyclopentyladenosine (CPA), an N6-substituted analog of adenosine, was examined in vitro. CPA bound with high affinity (K
d=0.48 nmol/l) to rat brain membranes. Specific binding, which represented 90–97% of the total counts bound at a ligand concentration of 1 nmol/l, was saturable, reversible and sensitive to protein denaturation. The pharmacology of binding was consistent with the labeling of an A-1 receptor, the R- and S-diastereomers of N6-phenylisopropyladenosine (PIA) showing a sixteenfold difference in their ability to displace CPA. The prototypic A-1 selective adenosine agonist, N6-cyclohexyladenosine (CHA) was twofold less active than CPA in displacing radiolabeled CPA. Comparison of the ability of cold CHA and CPA to displace [3H]-CPA gave rat dissociation constants of 1.88 and 1.80×104 s–1, respectively suggesting that both CHA and CPA bound to the same recognition site. In contrast however, comparison of the binding of [3H]-CPA with that of [3H]-CHA showed distinct differences. The K
d for CHA was approximately twice that of CPA while the apparent B
max was 60% greater. In comparing the pharmacology of CPA binding with that of CHA, it was found that CHA, S-PIA and the antagonist, PACPX were more active in displacing CHA than CPA. In general however, CPA has a binding profile very similar to that observed with CHA.Abbreviations 2-CADO
2 chloroadenosine
- CHA
N6cyclohexyladenosine
- CPA
N6cyclopentyladenosine
- EHNA
Erythro-9-(2-hydroxy-3-nonyl)adenine
- IBMX
Isobutylmethylxanthine
- NECA
5 N-ethylcarboxamide adenosine
- PACPX
[1,3-dipropyl-8-(2-amino-4-chloro)phenylxanthine]
- PIA
N6-Phenylisopropyladenosine 相似文献
3.
The development of adenosine A1 and A2B receptors on the longitudinal muscle and muscularis mucosae of the neonatal rat distal colon has been investigated using
homogenate binding, quantitative autoradiography and functional studies. In homogenate binding studies 1,3-[3H]-dipropyl-8-cyclopentylxanthine ([3H]DPCPX) bound with high affinity to A1 receptors in the muscularis mucosae and intact colon from rats aged 10, 15, 20, 25 and 30 days. The affinity of [3H]DPCPX was similar to that in the adult at all ages, but the density of binding sites was higher in the neonatal tissues.
Quantitative autoradiography showed a higher density of [3H]DPCPX binding sites in the longitudinal muscle than in the muscularis mucosae at all ages studied (day 10 to adult), and
this binding was concentration-dependently displaced by N
6-cyclopentyladenosine (CPA). In functional studies the longitudinal muscle relaxed in response to 5’-N-ethylcarboxamidoadenosine (NECA) and CPA at all ages studied (15–30 days), NECA being more potent than CPA. The potency of
NECA remained constant and it was antagonised by 1 μM DPCPX at all ages with pA
2-values consistent with activation of A2 receptors. The inactivity of 2-[p-(carboxyethyl)-phenylethylamino]-5’-N-ethylcarbox-amidoadenosine (CGS 21680) indicated that the A2 receptors were of the A2B subtype. The muscularis mucosae contracted in response to CPA at all ages studied (day 15 to adult) and the antagonism by
DPCPX (10 nM) were consistent with activation of A1 receptors. In conclusion, binding, autoradiographic and functional studies identified A1 receptors on the rat colon muscularis mucosae at all ages studied. However, while binding and autoradiographic localisation
showed the presence of A1 receptors in the longitudinal muscle at all ages studied, functional data only revealed the presence of A2B receptors.
Received: 3 July 1998 / Accepted: 25 November 1998 相似文献
4.
5.
Ulrich Schwabe Volker Lenschow Dieter Ukena David R. Ferry Hartmut Glossmann 《Naunyn-Schmiedeberg's archives of pharmacology》1982,321(1):84-87
Summary N6-p-Hydroxyphenylisopropyladenosine (HPIA) has been labelled with carrier-free Na[125I] to very high specific activity (2,175 Ci/mmol) and used as an agonist ligand to characterize Ri adenosine receptors in rat cerebral cortex membranes. The binding is saturable, reversible, stereospecific and dependent on protein concentration. The specific binding at 37°C was of high affinity with an equilibrium dissociation constant KD of 0.48 nmol/l and was saturable with 0.23 pmol of [125I]HPIA per mg of protein. The rate constant of association, k1, was 3.25×108 l mol–1 min–1 and that of dissociation, k2, 0.0110 min–1 yielding a t1/2 of 63 min. In competition experiments the (–)isomer of N6-phenylisopropyladenosine (PIA) was 16-fold more potent than the (+)isomer in competing for the binding sites. Specific binding was most effectively displaced by N6-cyclohexyladenosine (CHA, ki=0.26 nmol/l), (–)PIA (ki=0.33 nmol/l) and HPIA (ki=0.52 nmol/l), whereas 5-N-ethylcarboxamidoadenosine (NECA, ki-1.42 nmol/l) was less effective. The methylxanthines 3-isobutyl-1-methylxanthine (IBMX), theophylline and caffeine which have been classified as adenosine antagonists had ki values between 5–34 mol/l. Binding of [125I]HPIA was regulated by guanine nucleotides and divalent cations. The results indicate that [125I]HPIA labels Ri adenosine receptors in rat brain membranes. 相似文献
6.
The effects of adenosine, 5'-(N-ethyl)carboxamidoadenosine (NECA), 2-chloroadenosine (2-CA), No-cyclohexyladenosine (CHA) and N6(R-2-phenylisopropyl)-adenosine (R-PIA) on the tone of phenylephrine-constricted guinea-pig isolated aorta have been examined. For aortic relaxation the analogues exhibited the following rank order of potency: NECA > adenosine > 2-CA > R-PIA > CHA. This is consistent with previous reports that relaxation of this tissue is mediated by the adenosine A2 receptor. An unexpected finding was that R-PIA, 2-CA and CHA all induced contractions at concentrations lower than were required for relaxation, giving a biphasic dose-response curve. Neither NECA nor adenosine contracted the aorta. This is consistent with activation of vascular A1 receptors. An A1-selective concentration of the antagonist l,3-dipropyl-8-cyclopentyl xanthine abolished the contraction elicited by R-PIA in the guinea-pig aorta. This further suggests that the contraction is mediated by a1 receptors. 相似文献
7.
Joachim Neumann Wilhelm Schmitz Hasso Scholz Birgitt Stein 《Naunyn-Schmiedeberg's archives of pharmacology》1989,340(6):689-695
Summary In the present study the effects of adenosine analogues were investigated on cAMP content and contractile response in guinea-pig ventricular myocytes. The adenosine analogues (–)-N6-phenylisopropyladenosine (R-PIA), 5-N-ethylcarboxamideadenosine (NECA) and (+)-N6-phenyl-isopropyladenosine (S-PIA) in the presence of 0.01 mol/l isoprenaline reduced contractile response concentration-dependently. R-PIA and NECA were about equipotent (IC25: 0.01 mol/l and 0.039 mol/l respectively), while S-PIA was less potent (IC25: 0.6 mol/l). Isoprenaline stimulated cAMP content was reduced by R-PIA (IC25: 0.004 mol/l) and with lower potency by S-PIA (IC25: 0.15 mol/l) but the extent of reduction of cAMP by R-PIA and S-PIA (to 55% and 64% respectively) was less than the reduction of contractile response (to 26% and 55% respectively). This suggests that the effects of R- and S-PIA on contractile response are only in part due to a reduction in cAMP content. In addition, NECA did not decrease cAMP content but decreased contractile response to the same extent as R-PIA. Similar results were obtained in the presence of the phosphodiesterase inhibitor Ro 20-1724. Time course studies revealed that the effects of R-PIA (1 mol/l) on cAMP content and contractile response coincided reaching steady state after 5 min and remained stable thereafter. The effects of NECA (1 µmol/l) on contractility also reached steady state within 5 min, whereas it did not change cAMP content. It is concluded that the reduction of contractility by adenosine analogues in the presence of isoprenaline can only in part be explained by a reduction of cAMP content. It is suggested that a cAMP-independent effect, possibly an activation of phosphatases, might be involved additionally.Abbreviations R-PIA
(–)-N6-phenylisopropyladenosine
- NECA
5-N-ethylcarboxamideadenosine
- S-PIA
(+)-N6-phenylisopropyl-adenosine
- Ro 20-1724
4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone
Send offprint requests to J. Neumann at the above address 相似文献
8.
Paolo Barili Damiano Zaccheo Francesco Amenta 《European journal of pharmacology》1996,310(2-3):129-135
The pharmacological profile and the anatomical localization of dopamine D1-like and D2-like receptors were studied in sections of rat adrenal medulla, with radioligand binding and autoradiographic techniques, respectively. [3H]([R]-(+)-chloro-2,3,4,5-tetrahydro-5-phenyl-1H-3benzazepin-al hemimaleate) (SCH 23390) was used as a ligand for dopamine D1-like receptors and [3H]spiperone was used as a ligand for dopamine D2-like receptors. Radioligand binding and light microscope autoradiography did not show specific [3H]SCH 23390 binding in sections of rat adrenal medulla. This suggests that rat adrenal medulla does not express dopamine D1-like receptors. [3H]Spiperone was specifically bound to sections of rat adrenal medulla. The binding was time-, temperature- and concentration-dependent, with a dissociation constant (Kd) of 1.05 nM and a maximum density of binding sites (Bmax) of 100.2 ± 3.8 fmol/mg tissue. The pharmacological profile of [3H]spiperone binding to rat adrenal medulla was similar to that displayed by neostriatum, which is known to express dopamine D2 receptors. Light microscope autoradiography showed the accumulation of specifically bound [3H]spiperone as silver grains within sections of adrenal medulla. Silver grains were found primarily over the cellular membrane of chromaffin cells. The above data indicate that chromaffin cells of the rat adrenal medulla express dopamine receptors belonging to the dopamine D2 receptor subtype. These receptors are probably involved in the modulation of catecholamine release from chromaffin cells, as documented by functional studies. 相似文献
9.
E. Hüttemann D. Ukena V. Lenschow U. Schwabe 《Naunyn-Schmiedeberg's archives of pharmacology》1984,325(3):226-233
Summary Adenosine receptors in human platelet membranes have been characterized by radioligand binding and measurement of adenylate cyclase activity. Binding of 5-N-ethylcarboxamido[3H]adenosine ([3H]NECA) was rapid, reversible and dependent on protein concentration, pH and temperature. Due to a rapid rate of dissociation (t
1/2 approximately 20 s) binding was highest at 0° C. Adenosine deaminase and GTP alone did not influence [3H]NECA binding, whereas several divalent cations decreased binding. Saturation experiments revealed two different binding sites for [3H]NECA, with K
d values of 0.16 and 2.9 mol/l and B
max values of 8.4 and 33.4 pmol/mg of protein. In competition experiments NECA was the most potent adenosine agonist (IC50 0.5 mol/l), followed by 2-chloroadenosine (IC50 6.3 mol/l) and adenosine (IC50 12mol/l). A similar rank order of potencies was observed for the stimulatory effect of adenosine analogues on platelet adenylate cyclase. NECA stimulated adenylate cyclase activity with an EC50 value of 0.5 mol/l and was approximately 4-fold more potent than (–)N6-phenylisopropyladenosine [(–)PIA]. However, (–)PIA and N6-cyclohexyladenosine did not significantly affect [3H]NECA binding, an observation not consistent with the stimulatory effect on adenylate cyclase. The adenosine antagonists 3-isobutyl-1-methylxanthine, theophylline and caffeine showed IC50 values between 98 and 5,600 mol/l. [3H]PIA bound to platelet membranes with very low affinity and was not displaced by NECA. The [3H]NECA binding to human platelet membranes satisfies essential criteria for R
a adenosine receptors and, with some limitations, should be of value for the characterization of adenosine receptors in R
a subtype selective cells. 相似文献
10.
R. A. Cunha M. D. Constantino A. M. Sebastião B. Johansson B. B. Fredholm 《Naunyn-Schmiedeberg's archives of pharmacology》1996,353(3):261-271
The binding of the adenosine A2A receptor selective agonist 2-[4-(2-p-carboxyethyl) phenylamino]-5-N-ethylcarboxamidoadenosine (CGS 21680) to the rat hippocampal and cerebral cortical membranes was studied and compared with that to striatal membranes. [3H] CGS 21680, in the concentration range tested (0.2–200 nM), bound to a single site with a K
d of 58 nM and a B
max of 353 fmol/mg protein in the hippocampus, and with a K
d of 58 nM and a B
max of 264 fmol/mg protein in the cortex; in the striatum, the single high-affinity [3H] CGS 21680 binding site had a K
d of 17 nM and a B
max of 419 fmol/mg protein. Both guanylylimidodiphosphate (100 M) and Na+ (100 mM) reduced the affinity of [3H] CGS 21680 binding in the striatum by half and virtually abolished [3H] CGS 21680 binding in the hippocampus and cortex. The displacement curves of [3H] CGS 21680 binding with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), N
6-cyclohexyladenosine (CHA), 5-N-ethyl-carboxamidoadenosine (NECA) and 2-chloroadenosine (CADO) were biphasic in the hippocampus and cortex as well as in the striatum. The predominant [3H]CGS 21680 binding site in the striatum (80%) had a pharmacological profile compatible with A2A receptors and was also present in the hippocampus and cortex, representing 10–25% of [3H]CGS 21680 binding. The predominant [3H]CGS 21680 binding site in the hippocampus and cortex had a pharmacological profile distinct from A2A receptors: the relative potency order of adenosine antagonists DPCPX, 1,3-dipropyl8-{4-[(2-aminoethyl)amino]carbonylmethyloxyphenyl} xanthine (XAC), 8-(3-chlorostyryl) caffeine (CSC), and (E)-1,3-dipropyl-8-(3,4-dimethoxystyryl)-methylxanthine (KF 17,837) as displacers of [3H] CGS 21680 (5 nM) binding in the hippocampus and cerebral cortex was DPCPX > XAC CSC KF 17,837, and the relative potency order of adenosine agonists CHA, NECA, CADO, 2-[(2-aminoethylamino)carbonylethylphenylethylamino]-5-N-ethylcar-boxamidoadenosine (APEC), and 2-phenylaminoadenosine (CV 1808) was CHA NECA CADO > APEC CV1808 > CGS 21680. In the presence of DPCPX (20 nM), [3H] CGS 21680 (0.2-200 nM) bound to a site (A2A-like) with a K
d of 20 nM and a B
max of 56 fmol/mg protein in the hippocampus and with a K
d of 22 nM and a B
max of 63 fmol/mg protein in the cortex. In the presence of CSC (200 nM), [3H]CGS 21680 (0.2–200 nM) bound to a second high-affinity site with a K
d of 97 nM and a B
max of 255 fmol/mg protein in the hippocampus and with a K
d of 112 nM and a B
max of 221 fmol/mg protein in the cortex. Two pharmacologically distinct [3H]CGS 21680 binding sites were found in synaptosomal membranes of the hippocampus and cortex and in the striatum, one corresponding to A2A receptors and the other to the second high-affinity [3H]CGS 21680 binding site. In contrast, the pharmacology of [3H]CHA binding was similar in synaptosomal membranes of the three brain areas. The present results establish the existence of at least two high-affinity [3H]CGS 21680 binding sites in the CNS and demonstrate that the [3H]CGS 21680 binding site predominant in the hippocampus and cerebral cortex has different binding characteristics from the classic A2A adenosine receptor, which predominates in the striatum. 相似文献
11.
Anna Lorenzen Sigrid Grün Heidrun Vogt Ulrich Schwabe 《Naunyn-Schmiedeberg's archives of pharmacology》1992,346(1):63-68
Summary In solubilized extracts from bovine striatal membranes three different binding sites for 5-N-ethylcarboxamidoadenosine ([3H]NECA) were observed after separation of the extract by gel filtration on Sepharose CL-6B. The first peak was eluted in the void volume and contained the AZ adenosine receptor. In the second peak, [3H]NECA binding sites were eluted with a pharmacological profile characteristic of adenotin, a low affinity non-receptor adenosine binding protein. The third peak represented approximately 50% of the [3H]NECA binding activity. This site bound [3H]NECA in a reversible and saturable manner with K
D
of 17 nmol/l and a binding capacity of 11.3 pmol/mg protein. In competition experiments, adenosine, NECA, NAD, nnosine, 5-AMP and S-adenosyl-L-homocysteine were the most potent ligands. In contrast to adenosine receptors, this site did neither bind adenosine receptor antagonists nor the A2 selective agonist CGS 21,680 (2-[p-(2-carboxyethyl)phenethylamino]5-N-ethylcarboxamidoadenosine). These results suggest the existence of a novel high affinity binding site for adenosine of unknown function in bovine striatum.Abbreviations AMPPCP
,-methyleneadenosine-5-triphosphonate
- CCPA
2-chloro-N6-cyclopentyladenosine
- CHAPS
3-[3-(cholamidopropyl)dimethylammonio]-1-propanesulfonate
- CGS 21,680
2-[p-(2-carboxyethyl)phenethylamino]-5-N-ethylcarbox-amidoadenosine
- CPA
N6-cyclopentyladenosine
- DPCPX
1,3-dipropyl-8-cyclopentylxanthine
- GppNHp
guanosine-5-[,-imido]triphosphate
- GTP[S]
guanosine-5-O-(3-thiotriphosphate)
- NBTI
S-4-nitrobenzyl-6-thioinosine
- NECA
5-N-ethylcarbox-amidoadenosine
- NECG
5-N-ethylcarboxamidoguanosine
- PIA
N6-phenylisopropyladenosine
- SAH
S-adenosyl-L-homocysteine
- XAC
8-{4-[([{(2-aminoethyl)-amino}carbonyl]-methyl)oxy]-phenyl}-1,3-dipropylxanthine
Send offprint requests to A. Lorenzen at the above address 相似文献
12.
Martin J. Lohse Volker Lenschow Ulrich Schwabe 《Naunyn-Schmiedeberg's archives of pharmacology》1984,326(1):69-74
Summary The effects of barbiturates on radioligand binding to inhibitory R
i adenosine receptors of rat brain membranes were investigated. Binding of the adenosine receptor agonist (–)N6-phenylisopropyl[3H]adenosine and the antagonist 1,3-diethyl-8-[3H]phenylxanthine was inhibited by several barbiturates. This inhibition was concentration-dependent and occurred in the range of pharmacologically effective concentrations. Pentobarbital was the most potent of the barbiturates tested with a K
i of 92 mol/l. The (+)isomers of hexobarbital and mephobarbital were more potent than the respective (–)isomers. Barbituric acid itself did not displace either radioligand in concentrations up to 1 mmol/l. The inhibitory effect of pentobarbital was reversed by a single wash of membranes preincubated with the barbiturate. The presence of pentobarbital caused a decrease of the affinity of the receptor for the antagonist radioligand but did not alter the number of binding sites, suggesting a competitive antagonism. The effects of pentobarbital on radioligand binding to the receptor were not changed by the presence of picrotoxinin nor by the absence of chloride ions. This indicates that they are not mediated via the picrotoxinin binding site. The barbiturates could not be classified as either agonists or antagonists at the R
i adenosine receptor. The presence of GTP did not influence the inhibition of radioligand binding by pentobarbital; this is also observed for antagonists, whereas the affinity of agonists is markedly reduced by GTP. Binding of antagonists to the receptor is enthalpy-driven; the interaction of pentobarbital with the receptor was entropy-driven and the same was true for agonists. Thus, the interaction of pentobarbital with R
i adenosine receptors of rat brain membranes differs from that of both adenosine agonists and antagonists. Our data suggest that R
i adenosine receptors may be involved in the mediation of the effects of barbiturates. 相似文献
13.
Martin J. Lohse Karl-Norbert Klotz Ulrich Schwabe Gloria Cristalli Sauro Vittori Mario Grifantini 《Naunyn-Schmiedeberg's archives of pharmacology》1988,337(6):687-689
Summary 2-Chloro-N6-cyclopentyladenosine (CCPA) was synthesized as a potential high affinity ligand for A1 adenosine receptors. Binding of [3H]PIA to A1 receptors of rat brain membranes was inhibited by CCPA with a K
i-value of 0.4 nM, compared to a K
i-value of 0.8 nM for the parent compound N6-cyclopentyladenosine (CPA). Binding of [3H]NECA to A2 receptors of rat striatal membranes was inhibited with a K
i-value of 3900 nM, demonstrating an almost 10,000-fold A1-selectivity of CCPA.CCPA inhibited the activity of rat fat cell membrane adenylate cyclase, a model for the A1 receptor, with an IC50-value of 33 nM, and it stimulated the adenylate cyclase activity of human platelet membranes with an EC50-value of 3500 nM. The more than 100-fold A1-selectivity compares favourably with a 38-fold selectivity of CPA. Thus, CCPA is an agonist at A1 adenosine receptors with a 4-fold higher selectivity and 2-fold higher affinity than CPA, and a considerably higher selectivity than the standard A1 receptor agonist R-N6-phenylisopropyladenosine (R-PIA). CCPA represents the agonist with the highest selectivity for A1 receptors reported so far.Abbreviations CCPA
2-choro-N6-cyclopentyladenosine
- CPA
N6-cyclopentyladenosine
- NECA
5-N-ethylcarboxamidoadenosine
- PIA
N6-phenylisopropyladenosine
Send offprint requests to M. J. Lohse at the above address 相似文献
14.
Receptors in rat brain membranes which specifically bind 3H-diazepam were characterized pharmacologically using reference substances representing several pharmacological classes of drugs. Of 28 benzodiazepines tested, several “classical” ones (diazepam, clonazepam, lorazepam, oxazepam, nitrazepam, flurazepam, bromazepam and chlorazepate) with known clinical efficacy, as well as three newer “triazolo” benzodiazepines (estazolam, U 35,005, U 31,957), one new “imidazolo” benzodiazepine, U 31,219, and one new 2-carbamoylmethylene-benzodiazepine, displaced 3H-diazepam binding at low concentrations (Ki = 1–60 nM). For these benzodiazepines there was a statistically significant correlation between Ki values for displacement and ED50 (or MED) values in several pharmacological tests predictive of anxiolytic activity in man. More than 100 nonbenzodiazepines, representing 22 distinct pharmacological classes as well as 14 presumed neurotransmitters in the CNS, including 4 peptides, were much weaker as 3H-diazepam displacers (Ki > 0.1 nM). These results that in vitro 3H-diazepam binding represents the physiologically relevant binding to hitherto unknown receptors in the CNS. 相似文献
15.
Comparison of A1 adenosine receptors in brain from different species by radioligand binding and photoaffinity labelling 总被引:5,自引:0,他引:5
Karl-Norbert Klotz Heidrun Vogt Hoda Tawfik-Schlieper 《Naunyn-Schmiedeberg's archives of pharmacology》1991,343(2):196-201
Summary Radioligand binding to A1 adenosine receptors at brain membranes from seven species was investigated. The antagonist 8-cyclopentyl-1,3-[3H]dipropyl-xanthine ([3H]DPCPX) bound with affinities between 0.17 nM in sheep brain and 2.1 nM in guinea pig brain. Competition of several antagonists for [3H]DPCPX binding showed that the most potent compounds were DPCPX with K
i values of 0.05 nM in bovine brain and 1.1 nM in guinea pig brain and xanthine amine congener (XAC) with K
i values of 0.03 nM in bovine brain and 5.5 nM in guinea pig brain. The differences in affinity of the agonist radioligand 2-chloro-N
6-[3H]cyclopentyl-adenosine ([3H]CCPA) were less pronounced, ranging from a K
D value of 0.12 nM (hamster brain) to 0.42 nM (guinea pig brain). Agonist competition for [3H]DPCPX binding of photoaffinity labelling, however, exhibited marked species differences. N-Ethylcarboxamidoa-denosine (NECA) and S-N
6-phenylisopropyladenosine (S-PIA) showed 20 to 25-fold different K
D values in different species. NECA had a particularly high affinity in guinea pig brain and was only two-fold less potent than R-PIA. Thus, the difference from the classical A1 receptor profile (R-PIA > -NECA > S-PIA) is not sufficient to speculate that A1 receptor subtypes may exist that are coupled to different effector systems. Our data show that these difference can easily be explained by species differences. 相似文献
16.
Summary A variety of alkylxanthines has been comparatively examined as antagonists of A1 adenosine receptors in rat fat cells, rat and bovine cerebral cortex and of A2 adenosine receptors in human platelets. With few exceptions all xanthine derivatives with 7-position substituents such as diprophylline, proxyfylline, pentoxifylline and etofylline were less potent antagonists than xanthine itself which hadK
i-values of 170 mol/l (A1) and 93 mol/l (A2). Theophylline, caffeine and 3-isobutyl-1-methylxanthine were more potent than xanthine but nearly equipotent antagonists at both receptor subtypes. 8-Phenyl substituents considerably increased the antagonist potency at A1 and A2 receptors. 1,3-Diethyl-8-phenylxanthine was the most potent A2 antagonist (K
i 0.2 mol/l) in human platelets. At A1 receptors 1,3-dipropyl-8-(2-amino-4-chlorophenyl)xanthine (PACPX) was the most potent antagonist in all three tissues withK
i-values from 0.3 to 8.6 nmol/l. Several 8-phenylxanthine derivatives were remarkably selective antagonists at A1 receptors. 8-Phenyltheophylline was approximately 700 times more potent as antagonist at A1 receptors (bovine brain) than at A2 receptors (human platelets), and PACPX was even 1,600 times more potent as A1 adenosine receptor antagonist. These compounds offer a possibility for a subtype-selective blockade of adenosine receptors. 相似文献
17.
Summary The modulation of radioligand binding at R
i adenosine receptors of rat fat cells by guanine nucleotides and cations was investigated. Guanine nucleotides (in the order of potency: GTP=GDP>Gpp(NH)p>5-GMP) decreased the binding of the R
i receptor agonist (–)N6-phenylisopropyl[3H]adenosine ([3H]PIA), but did not affect binding of the antagonist 1,3-diethyl-8[3H]phenylxanthine ([3H]DPX). Saturation of [3H]PIA binding revealed that GTP (100 mol/l) converts the high affinity form of the R
i receptor into a low affinity form. This effect was confirmed in kinetic experiments. GTP decreased the potency of agonists in competing for [3H]DPX binding, as shown by a 50-fold shift of the K
i-value for (–)PIA, whereas antagonist-induced inhibition of binding remained unchanged. The divalent cations Mg2+ and Ca2+ produced a slight increase in [3H]PIA binding but did not affect [3H]DPX binding. Mn2+ markedly decreased both agonist and antagonist binding at R
i adenosine receptors. Divalent cations reversed the guanine nucleotide-induced decrease of affinity of the R
i receptor. Na+ did not significantly affect agonist or antagonist binding but abolished the stimulatory effect of Mg2+ on agonist binding in the presence of GTP. Our data indicate that guanine nucleotides convert the R
i adenosine receptor of rat fat cells from a high to a low agonist affinity state and that the modulation of radioligand binding by mono-and divalent cations differs from that of R
i receptors of other tissues. 相似文献
18.
Two major subtypes of adenosine receptors occur in different tissues which have been distinguished by pharmacological and biochemical criteria. The A1 adenosine receptor has a high-affinity for adenosine and mediates inhibition of adenylyl cyclase, whereas the A2 adenosine receptor usually has a lower affinity and mediates stimulation of the enzyme. Furthermore, evidence has been obtained that A1 receptors increase the conductance of receptor-regulated potassium channels, induce inactivation of calcium channels, and modulate the breakdown of phosphoinositides by phospholipase C. Selective agonists and antagonists have been developed for both receptor subtypes. In addition, both adenosine receptors have extensively been characterized by radioligand binding studies. Suitable radioligands for the A1 receptor are the agonist [3H]2-chloro-N6-cyclopentyladenoisine (CCPA) and the antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX)and for the A2a receptor [3H]2-[p-(carboxyethyl)phenethylamino]- 5′-N-carboxamidoadenosine (CGS 21860). Furthermore, photoaffinity ligands were developed from adenosine derivatives, which can be covalently incorporated into the binding unit of both receptor subtypes. With this approach, it has been shown that the A1 receptor has an apparent molecular weight of approximately 36 kDa and the A2a receptor of 45 kDa. A second approach to elucidate the structure of adenosine receptors involves the purification of receptor protein by affinity chromatography. With this procedure, cerebral A1 receptors have been purified to apparent homogeneity. More recently, the structure of receptor subtypes has been elucidated by cloning the receptors from a cDNA library. Furthermore, a novel adenosine binding with [3H] 5′ -N-ethylcarboxamidoadenosine ([3H]NECA). The pharmacological profile of this NECA-binding protein has been determined in competition experiments with adenosine receptor ligands. It can be distinguished from that of A2a adenosine receptors and other adenosine binding proteins. We propose the name Ax for this unique adenosine binding protein. © 1993 Wiley-Liss, Inc. 相似文献
19.
Solinas M Ferré S Antoniou K Quarta D Justinova Z Hockemeyer J Pappas LA Segal PN Wertheim C Müller CE Goldberg SR 《Psychopharmacology》2005,179(3):576-586
Rationale Caffeine is a non-selective adenosine receptor antagonist in vitro, but involvement of different adenosine receptor subtypes, particularly adenosine A1 and A2A receptors, in the central effects of caffeine remains a matter of debate.Objective Investigate the role of adenosine A1 and A2A receptors in the discriminative-stimulus effects of caffeine.Methods Rats were trained to discriminate an injection of 30 mg/kg (i.p.) caffeine from saline. The selective A1 receptor antagonist CPT, the selective A2A receptor antagonist MSX-3 and the non-selective adenosine receptor antagonist DMPX were assessed for their ability to produce caffeine-like discriminative effects. The ability of CPT, MSX-3, the A1 receptor agonist CPA and the A2A receptor agonist CGS21680 to reduce the discriminative effects of caffeine was also tested. Radioligand binding experiments with membrane preparations from rat striatum and transfected mammalian cell lines were performed to characterize binding affinity profiles of the different adenosine antagonists used in the present study (caffeine, DMPX, CPT and MSX-3) in relation to all known adenosine receptors (A1, A2A, A2B, A3).Results DMPX and CPT, but not MSX-3, produced significant caffeine-like discriminative effects. MSX-3, but not CPT, markedly reduced the discriminative effects of caffeine and the caffeine-like discriminative effects of CPT. Furthermore, the A1 receptor agonist CPA, but not the A2A agonist CGS21680, reduced caffeines discriminative effects.Conclusions Adenosine A1 receptor blockade is involved in the discriminative-stimulus effects of behaviorally relevant doses of caffeine; A2A receptor blockade does not play a central role in caffeines discriminative effects and counteracts the A1 receptor-mediated discriminative-stimulus effects of caffeine. 相似文献
20.
Pao-Luh Tao Chih-Shung Wong Mei-Chuan Lin 《Naunyn-Schmiedeberg's archives of pharmacology》1996,354(2):187-191
We have shown previously that systemic chronic morphine treatment causes down-regulation of spinal adenosine A1 receptors in rats. Recently, we have found that chronic supraspinal morphine treatment also causes this effect. In the present study, we investigated whether chronic spinal morphine treatment has the same effect of down-regulation of spinal adenosine A1 receptors. Adult male Sprague-Dawley rats were rendered tolerant to morphine either by multiple intrathecal (i.t.) injections or continuous Lt. infusion by osmotic pump administration for 2 or 4 days. Spinal A1-adenosine receptor binding activity was measured by using the selective A1 adenosine agonist [3H]cyclohexyladenosine. No significant decrease in [3H]cyclohexyladenosine binding was found in the spinal cord after 2 or 4 days of multiple Lt. injections of morphine. There was also no significant change in the amount of spinal [3H]cyclohexyladenosine bound after 4 days of continuous Lt. infusion of morphine by osmotic pump. From these and our previous results, it is concluded that only supraspinal chronic morphine treatment down regulates the spinal A1 adenosine receptor and this may play a role in the mechanism of supraspinal morphine tolerance but not spinal morphine tolerance. 相似文献