TY - JOUR A1 - Lohse, M. J. A1 - Klotz, Karl-Norbert A1 - Diekmann, E. A1 - Friedrich, K. A1 - Schwabe, U. T1 - 2',3'-Dideoxy-N\(^6\)-cyclohexyladenosine: an adenosine derivative with antagonist properties at adenosine receptors N2 - Tbe 2',3'-dideoxy analogue of the potent A\(_1\) receptor agonist, N\(^6\)-cyclohexyladenosine (CHA), was synthesized as a potential antagonist for the A\(_1\) adenosine receptor. In sturlies on adenylate cyclase 2',3'-dideoxy-N\(^6\)-cyclohexyladenosine (ddCHA) did not show agonist properties at A\(_1\) or at A\(_2\) receptors. However, it antagonized the inhibition by R-PIA of adenylate cyclase activity of fat cell membranes via A\(_1\) receptors with a K\(_i\) value of 13 \(\mu\)M. ddCHA competed for the binding of the selective A1 receptor antagonist, [\(^3\) HJ8-cyclopentyl-1,3-dipropylxantbine ([\(^3\)H]DPCPX), to rat brain membranes with a K\(_i\) value of 4.8 \(\mu\)M; GTP did not affect the competition curve. In contrast to the marked stereoselectivity of the A\(_1\) receptor for the cx- and the natural ß-anomer of adenosine, the cx-anomer of ddCHA showed a comparable affinity for the A\(_1\) receptor (K\(_i\) value 13.9 \8\mu\)M). These data indicate that the 2'- and 3'-hydroxy groups of adenosine and its derivatives are required foragonist activity at and high affinity binding to A\(_1\) adenosine receptors and for the distinction between the cx- and ß-forms. KW - Toxikologie KW - Adenosine receptors KW - Adenylate cyclase KW - Adenosine receptor antagonists Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60282 ER - TY - JOUR A1 - Cristalli, G. A1 - Eleuteri, A. A1 - Vittori, S. A1 - Volpini, R. A1 - Lohse, M. J. A1 - Klotz, Karl-Norbert T1 - 2-Alkynyl derivatives of adenosine and adenosine-5'-N-ethyluronamides as selective agonists at A\(_2\) adenosine receptors N2 - In the search for more selective A2-receptor agonists and on the basis that appropriate substitution at C2 is known to impart selectivity for A\(_2\) receptors, 2-alkynyladenosines 2a-d were resynthesized and evaluated in radioligand binding, adenylate cycla.se, and platelet aggregation studies. Binding of [\(^3\)H]NECA to A\(_2\) receptors of rat striatal membranes was inhibited by compounds 2a-d with K\(_i\) values ranging from 2.8 to 16.4 nM. 2-Alkynyladenosines also exhibited high-affmity binding at solubilized A\(_2\) receptors from human platelet membranes. Competition of 2-alkynyladenosines 2a-d for the antagonist radioligand [\(^3\)H]DPCPX and for the agonist [\(^3\)H]CCPA gave K\(_i\) values in the nanomolar range, and the compounds showed moderate A\(_2\) selectivity. In order to improve this selectivity, the correaponding 2-alkynyl derivatives of adenosine-5'-N-ethyluronamide 8a-d were synthesized and tested. A\(_1\) expected, the 5'-N-ethyluronamide derivatives retained the A\(_2\) affinity whereas the A\(_1\) affinity was attenuated, resulting in an up to 10-fold increase in A\(_2\) selectivity. A similar patternwas observed in adenylate cyclase assays andin platelet aggregation studies. A 30- to 45-fold selectivity for platelet A\(_2\) receptors compared to A\(_1\) receptors was found for compounds 8a-c in adenylate cyclase studies. KW - Toxikologie Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60412 ER - TY - JOUR A1 - Klotz, Karl-Norbert A1 - Lohse, M. J. A1 - Schwabe, U. A1 - Cristalli, G. A1 - Vittori, S. A1 - Grifantini, M. T1 - 2-Chloro-N\(^6\)-[\(^3\)H]cyclopentyladenosine ([\(^3\)H]CCPA) - a high affinity agonist radioligand for A\(_1\) adenosine receptors N2 - The tritiated analogue of 2-chloro-N6-cyclopentyladenosine (CCPA), an adenosine derivative with subnanomolar affinity and a 10000-fold selectivity for A1 adenosine receptors, has been examined as a new agonist radioligand. [3H]CCP A was prepared with a specifi.c radioactivity of 1.58 TBqjmmol ( 43 Ci/mmol) and bound in a reversible manner to A1 receptors from rat brain membranes with a high affinity K0 -value of 0.2 nmol/1. In the presence of GTP a K0 -value of 13 nmol/1 was determined for the low affinity state for agonist binding. Competition of several adenosine receptor agonists and antagonists for [3H]CCPA binding to rat brain membranes confrrmed binding to an A1 receptor. Solubilized A1 receptors bound [3H]CCPA with similar affinity for the high affinity state. At solubilized receptors a reduced association rate was observed in the presence of MgC12, as has been shown for the agonist [ 3H]N6-phenylisopropyladenosine ([3H]PIA). [3H]CCPA was also used for detection of A1 receptors in rat cardio myocyte membranes, a tissue with a very low receptor density. A K0 -value of 0.4 nmol/1 and a Bmax-value of 16 fmol/ mg protein was determined in these membranes. In human platelet membranes no specific binding of [3H]CCPA was measured at concentrations up to 400 nmoljl, indicating that A2 receptors did not bind [3H]CCPA. Based on the subnanomolar affinity and the high selectivity for A1 receptors [ 3H]CCPA proved to be a useful agonist radioligand for characterization of A 1 adenosine receptors also in tissues with very low receptor density. KW - Toxikologie KW - Adenosine receptors KW - Radioligauds KW - agonists Y1 - 1989 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60328 ER - TY - JOUR A1 - Lohse, M. J. A1 - Klotz, Karl-Norbert A1 - Schwabe, U. A1 - Cristalli, G. A1 - Vittori, S. A1 - Grifantini, M. T1 - 2-Chloro-N\(^6\)-cyclopentyladenosine: a highly selective agonist at A\(_1\) adenosine receptors N2 - 2-Chloro-N\(^6\)-cyclopentyladenosine (CCPA) was synthesized as a potential high affinity ligand for At adenosine receptors. Binding of [\(^3\)H]PIA to A1 receptors of rat brain membranes was inhibited by CCP A with a Ki-value of 0.4 nM, compared to a Ki-value of 0.8 nM for the parent compound N\(^6\)-cyclopentyladenosine (CPA). Binding of [\(^3\)H]NECA to A\(_2\) receptors of rat striatal membranes was inhibited with a Ki-value of 3900 nM, demonstrating an almost 10,000-fold A\(_1\)-selectivity of CCPA. CCP A inhibited the activity of rat fat cell membrane adenylate cyclase, a model for the A\(_1\) receptor, with an IC\(_{50}\)-value of 33 nM, and it stimulated the adenylate cyclase activity of human platelet membranes with an EC\(_{50}\)-value of 3500 nM. The more than 100-fold A\(_1\)-selectivity compares favourably with a 38-fold selectivity of CPA. Thus, CCPA is an agonist at A\(_1\) adenosine receptors with a 4-fold higher selectivity and 2-fold higher affinity than CPA, and a considerably higher selectivity than the standard At receptor agonist R-N\(^6\) -phenylisopropyladenosine (R-PIA). CCP A represents the agonist with the highest selectivity for A\(_1\) receptors reported so far. KW - Toxikologie KW - Adenosine receptors KW - Adenylate cyclase Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60279 ER - TY - JOUR A1 - Lohse, M. J. A1 - Klotz, Karl-Norbert A1 - Lindenborn Fotinos, J. A1 - Reddington, M. A1 - Schwabe, U. A1 - Olsson, R. A. T1 - 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX) - a selective high affinity antagonist radioligand for A\(_1\) adenosine receptors N2 - The properties of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as an antagonist ligand for A\(_1\) adenosirre receptors were examined and conipared with other radioligands for this receptor. DPCPX competitively antagonized both the inhibition of adenylate cyclase activity via A\(_1\) adenosirre receptors and the stimulationvia A\(_2\) adenosirre receptors. The K\(_i\)-values of this antagonism were 0.45 nM at the A\(_1\) receptor of rat fat cells, and 330 nM at the A\(_2\) receptor of human platelets, giving a more than 700-fold A\(_1\)-selectivity. A similar A\(_1\)-selectivity was determined in radioligand binding studies. Even at high concentrations, DPCPX did not significantly inhibit the soluble cAMPphosphodiesterase activity of human platelets. [\(^3\)H]DPCPX (105 Ci/mmol) bound in a saturable manner with high affinity to A\(_1\) receptors in membranes of bovine brain and heart, and rat brain and fat cells (K\(_D\) -values 50-190 pM). Its nonspecific binding was about 1% of total at K\(_D\) , except in bovine myocardial membranes (about 10%). Binding studies with bovine myocardial membranes allowed the analysis of both the high and low agonist affinity states of this receptor in a tissue with low receptor density. The binding properties of [\(^3\)H]DPCPX appear superior to those of other agonist and antagonist radioligands for the A\(_1\) receptor. KW - Toxikologie KW - Adenosine receptors KW - Adenylate cyclase KW - Phosphodiesterase KW - Xanthines KW - Radioligands Y1 - 1987 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60246 ER - TY - JOUR A1 - Bommakanti, R. K. A1 - Klotz, Karl-Norbert A1 - Dratz, E. A. A1 - Jesaitis, A. J. T1 - A carboxyl-terminal tail peptide of neutrophil chemotactic receptor disrupts its physical complex with G protein N2 - No abstract available KW - Toxikologie Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60456 ER - TY - JOUR A1 - Spinaci, Andrea A1 - Lambertucci, Catia A1 - Buccioni, Michela A1 - Dal Ben, Diego A1 - Graiff, Claudia A1 - Barbalace, Maria Cristina A1 - Hrelia, Silvana A1 - Angeloni, Cristina A1 - Tayebati, Seyed Khosrow A1 - Ubaldi, Massimo A1 - Masi, Alessio A1 - Klotz, Karl-Norbert A1 - Volpini, Rosaria A1 - Marucci, Gabriella T1 - A\(_{2A}\) adenosine receptor antagonists: are triazolotriazine and purine scaffolds interchangeable? JF - Molecules N2 - The A\(_{2A}\) adenosine receptor (A\(_{2A}\)AR) is one of the four subtypes activated by nucleoside adenosine, and the molecules able to selectively counteract its action are attractive tools for neurodegenerative disorders. In order to find novel A\(_{2A}\)AR ligands, two series of compounds based on purine and triazolotriazine scaffolds were synthesized and tested at ARs. Compound 13 was also tested in an in vitro model of neuroinflammation. Some compounds were found to possess high affinity for A\(_{2A}\)AR, and it was observed that compound 13 exerted anti-inflammatory properties in microglial cells. Molecular modeling studies results were in good agreement with the binding affinity data and underlined that triazolotriazine and purine scaffolds are interchangeable only when 5- and 2-positions of the triazolotriazine moiety (corresponding to the purine 2- and 8-positions) are substituted. KW - A\(_{2A}\) adenosine receptor antagonist KW - purine derivatives KW - triazolotriazine derivatives KW - anti-Parkinson agents KW - anti-inflammatory agents KW - molecular modeling Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-270618 SN - 1420-3049 VL - 27 IS - 8 ER - TY - CHAP A1 - Spielmann, W. S. A1 - Arend, L. J. A1 - Klotz, Karl-Norbert A1 - Schwabe, U. T1 - Adenosine control of the renal Collecting tubule: receptors and signaling N2 - No abstract available. KW - Adenosin Y1 - 1991 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86129 ER - TY - JOUR A1 - Cristalli, G. A1 - Franchetti, P. A1 - Grifantini, M. A1 - Vittori, S. A1 - Klotz, Karl-Norbert A1 - Lohse, M. J. T1 - Adenosine receptor agonists: Synthesis and biological evaluation of 1-deaza analogues of adenosine N2 - In a search for more selective A\(_1\) adenosine receptor agonists, N\(^6\)-[(R)-(-)-1-methyl-2-phenethyl]-1-deazaadenosine (1-deaza-R-PIA, 3a), N\(^6\)-cyclopentyl-1-deazaadenosine (1-deazaCPA, 3b), N\(^6\)-cyclohexyl-l-deazaadenosine (1-deazaCHA, Sc), and the corresponding 2-chloro derivatives 2a-c were synthesized from 5,7-dichloro-3-ß-D-ribofuranosyl-3Himidazo[ 4,5-b]pyridine (1). On the other band, N-ethyl-1'-deoxy-1'-(1-deaza-6-amino-9H-purin-9-yl)-ß-D-ribofuranuronamide (1-deazaNECA, 10) was prepared from 7-nitro-3-ß-D-ribofuranosyl-3H-imidazo[4,5-b]pyridine (4), in an attempt to find a more selective A\(_2\) agonist. The activity of all deaza analogues at adenosine receptors has been determined in adenylate cyclase andin radioligand binding studies. 1-DeazaNECA (10) proved tobe a nonselective agonist at both subtypes of the adenosine receptor. It is about 10-fold less active than NECA but clearly more active than the parent compound 1-deazaadenosine as an inhibitor of platelet aggregation and as a stimulator of cyclic AMP accumulation. The N\(^6\)-substituted 1-deazaadenosines largely retain the A\(_1\) agonist activity of their parent compounds, but lose some of their A\(_2\) agonist activity. This results in A\(_1\)-selective compounds, of which N\(^6\)cyclopentyl- 2-chloro-1-deazaadenosine (1-deaza-2-Cl-CPA, 2b) was identified as the most selective agonist at A\(_1\) adenosine receptors so far known. The activity of all 1-deaza analogues confirms that the presence of the nitrogen atom at position 1 of the purine ring is not critical for A\(_1\) receptor mediated adenosine actions. KW - Toxikologie Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60262 ER - TY - JOUR A1 - Vazquez-Rodriguez, Saleta A1 - Vilar, Santiago A1 - Kachler, Sonja A1 - Klotz, Karl-Norbert A1 - Uriarte, Eugenio A1 - Borges, Fernanda A1 - Matos, Maria João T1 - Adenosine receptor ligands: coumarin−chalcone hybrids as modulating agents on the activity of hARs JF - Molecules N2 - Adenosine receptors (ARs) play an important role in neurological and psychiatric disorders such as Alzheimer's disease, Parkinson's disease, epilepsy and schizophrenia. The different subtypes of ARs and the knowledge on their densities and status are important for understanding the mechanisms underlying the pathogenesis of diseases and for developing new therapeutics. Looking for new scaffolds for selective AR ligands, coumarin–chalcone hybrids were synthesized (compounds 1–8) and screened in radioligand binding (hA\(_1\), hA\(_{2A}\) and hA\(_3\)) and adenylyl cyclase (hA\(_{2B}\)) assays in order to evaluate their affinity for the four human AR subtypes (hARs). Coumarin–chalcone hybrid has been established as a new scaffold suitable for the development of potent and selective ligands for hA\(_1\) or hA\(_3\) subtypes. In general, hydroxy-substituted hybrids showed some affinity for the hA\(_1\), while the methoxy counterparts were selective for the hA\(_3\). The most potent hA\(_1\) ligand was compound 7 (K\(_i\) = 17.7 µM), whereas compound 4 was the most potent ligand for hA\(_3\) (K\(_i\) = 2.49 µM). In addition, docking studies with hA\(_1\) and hA\(_3\) homology models were established to analyze the structure–function relationships. Results showed that the different residues located on the protein binding pocket could play an important role in ligand selectivity. KW - coumarin KW - chalcone KW - neurodegenerative diseases KW - adenosine receptors KW - binding affinity KW - docking Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-213165 SN - 1420-3049 VL - 25 IS - 18 ER - TY - CHAP A1 - Spielmann, W.-S. A1 - Arend, L. J. A1 - Klotz, Karl-Norbert A1 - Schwabe, U. T1 - Adenosine receptors and singnaling in the kidney N2 - No abstract available. KW - Adenosinrezeptor KW - Niere Y1 - 1990 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86114 ER - TY - JOUR A1 - Lohse, Martin J. A1 - Klotz, Karl-Norbert A1 - Salzer, Manfred J. A1 - Schwabe, Ulrich T1 - Adenosine regulates the \(Ca^{2+} \) sensitivity of mast cell mediator release : (histamine secretion/inositol phosphates/calcium) JF - Proceedings of the National Academy of Sciences of the United States of America N2 - Mast cells release histamine and other mediators of allergy in response to stimulation of their IgE receptors. This release is generally thought to be mediated by an elevation of cytosolic \(Ca^{2+}\). Recent evidence suggests that there might be factors that modulate the coupling between \(Ca^{2+}\) levels and mediator release. The present report identifies adenosine as one such modulator. Adenosine and several of its metabolically stable analogues were shown to enhance histamine release from rat peritoneal mast cells in response to stimuli such as concanavalin A. Metabolizing endogenous adenosine with adenosine deaminase dampened the response to stimuli, whereas trapping endogenous adenosine inside mast cells with nucleoside-transport inhibitors markedly enhanced stimulated histamine release. The metabolically stable adenosine analogue 5' -(N-ethylcarboxamido)adenosine (NECA) did not affect the initial steps in the sequence from IgE-receptor activation to mediator release, which are generation of inositol trisphosphate and increase of cytosolic \(Ca^{2+}\). However, NECA did enhance the release induced in ATP-permeabilized cells by exogenous \(Ca^{2+}\), but it had no effect on the release induced by phorbol esters. These data suggest that adenosine sensitizes mediator release by a mechanism regulating stimulus-secretion coupling at a step distal to receptor activation and second-messenger generation. Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-127883 VL - 85 ER - TY - JOUR A1 - Lohse, M. J. A1 - Böser, S. A1 - Klotz, Karl-Norbert A1 - Schwabe, U. T1 - Affinities of barbiturates for the GABA-receptor complex and A\(_1\) adenosine receptors: A possible explanation of their excitatory effects N2 - The effects of barbiturates on the GABA·receptor complex and the A\(_1\) adenosine receptor were studied. At the GABA-receptor complex the barbiturates inhibited the binding of [\(^{35}\)S]t-butylbicyclophosphorothionate [\(^{35}\)S]TBPT) and enhanced the binding of [\(^3\)H]diazepam. Kinetic and saturation experiments showed that both effects were allosteric. Whereas all barbiturates caused complete inhibition of [\(^{35}\)S]TBPT binding, they showed varying degrees of maximal enhancement of [\(^3\)H]diazepam binding; (±)methohexital was idenafied as the most efficacious compound for this enhancement. At the A\(_1\) adenosine receptor all barbiturates inhibited the binding of [\(^3\)H]N\(^6\)-phenylisopropyladenosine (\(^3\)H]PIA) in a competitive manner. The comparison of the effects on [\(^3\)H]diazepam and [\(^3\)H]PIA binding showed that excitatory barbiturates interact preferentially with the A\(_1\) adenosine receptor, and sedative/anaesthetic barbiturates with the GABA-receptor complex. It is speculated that the interaction with these two receptors might be the basis of the excitatory versus sedative/ anaesthetic properties of barbiturates. KW - Toxikologie KW - GABA-receptor complex KW - Adenosine receptors KW - Barbiturates Y1 - 1987 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60250 ER - TY - JOUR A1 - Lohse, Martin J. A1 - Klotz, Karl-Norbert A1 - Schwabe, Ulrich T1 - Agonist photoaffinity labeling of A1 adenosine receptors: Persistent activation reveals spare receptors N2 - No abstract available. KW - Pharmazie KW - Pharmakologie Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-87966 ER - TY - JOUR A1 - Lohse, M. J. A1 - Klotz, Karl-Norbert A1 - Jakobs, K. H. A1 - Schwabe, U. T1 - Barbiturates are selective antagonists at A\(_1\) adenosine receptors N2 - Barbiturates in pharmacologically relevant . concentrations inhibit binding of (R)-\(N^6\)-phenylisopropyl[\(^3\)H]adenosine ([\(^3\)H]PIA) to solubilized A\(_1\) adenosine receptors in a concentration-dependent, stereospecific, and competitive manner. K\(_i\) values are similar to those obtained for membrane-bound receptors and are 31 \(\mu\)M for ( ± )-5-(1 ,3-dimethyl)-5-ethylbarbituric acid [( ± )DMBB] and 89 \(\mu\)M for ( ± )-pentobarbital. Kinetic experiments demoostrate that barbiturates compete directly for the binding site of the receptor. The inhibition of rat striatal adenylate cyclase by unlabelled (R)-\(N^6\)-phenylisopropyladenosine [(R)-PIA] is antagonized by barbiturates in the same concentrations that inhibit radioligand binding. The Stimulation of adenylate cyclase via A\(_2\) adenosine receptors in membranes from NIE 115 neuroblastoma cells is antagonized only by 10-30 times higher concentrations of barbiturates. lt is concluded that barbiturates are selective antagonists at the A1 receptor subtype. In analogy to the excitatory effects of methylxanthines it is suggested that A\(_1\) adenosine receptor antagonism may convey excitatory properties to barbiturates. Key Words: Adenosine receptors-Barbiturates - Adenylate cyclase-Receptor solubilization-[3H]PIA binding-N1E 115 cells. Lohse M. J. et al. Barbiturates are selective antagonists at A1 adenosine receptors. KW - Toxikologie KW - adenosine receptors KW - barbiturates KW - adenylate cyclase KW - receptor solubilization KW - N1E 115 cells KW - [3H]PIA binding Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60187 ER - TY - JOUR A1 - van Calker, D. A1 - Steber, R. A1 - Klotz, Karl-Norbert A1 - Greil, W. T1 - Carbamazepine distinguishes between adenosine receptors that mediate different second messenger responses N2 - The mechanism of the therapeutic and prophylactic effects of carbamazepine (CBZ) in affective psychoses is unknown but may in part be related to the potent competitive interaction of CBZ with adenosine-binding sites in the brain. The antioonvulsant and sedative properties of CBZ are reminiscent of the effects evoked by adenosine-agonists and contrast sharply with the opposite aclions of adenosine-antagonists like caffeine. However. indirect evidence suggests an antagonist- rather than an agonist-like activity of CBZ at adenosi11e-receptors. We have used various model systems, in which adenosine receptor subtypes mediate different second messenger-responses, to investigate this apparent paradox. CBZ was found to antagonize the A\(_1\) receptor-mediated inhibition of cydic AMP accumulation in cultured astroblasts and in GH3-cells. Furthermore, CBZ also inhibits the adenosine-induced increase in the level of cyclic AMP in cultured astroblasts, which is mediated by low-affinity A\(_{2b}\)-receptors. ln contrast, CBZ does not block the inhibition elicited by adenosine-agonists of the agonist-induced increased formation of inositolphosphates in human neutrophils, which is mediated by high-affinity A\(_{2a}\)-receptors. The specific antagonism by CBZ of A\(_1\)- but not of high-affinity A\(_{2a}\)-receptors was further supported by binding experiments using rat brain membranes. These results suggest tbat the paradox of CBZ's antagonistic effects at adenosine-receptors might be at least partially reconciled by a selective antagonistic action of CBZ at A\(_1\)recertors but not at high-affinity A\(_{2a}\)-receptors. KW - Toxikologie Y1 - 1991 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60392 ER - TY - JOUR A1 - Gonzalez-Calero, G. A1 - Cubero, A. A1 - Klotz, Karl-Norbert T1 - Characterization and photoaffinity labeling of A1 adenosine receptors in coated visicles form bovine brain N2 - The antagonist (3 II ) DPCPX exhi bitcd a Kd of 0. 4 nM at coalcd vcsicles from bovine brain. Agonist compelition for ( 3 11) DPCPX bind in~ revcaled two affini ty slales for gonists. The pholoaffinity probe I25 I -AHPIA specifically labelled a band with a molecular weight of 35 Kd. KW - Pharmakologie Y1 - 1991 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86004 ER - TY - JOUR A1 - Spielman, William S. A1 - Klotz, Karl-Norbert A1 - Arend, Lois J. A1 - Olson, Barbara A. A1 - LeVier, David G. A1 - Schwabe, Ulrich T1 - Characterization of adenosine A1 receptor in a cell line (28A) derived from the rabbit collecting tubule N2 - We have previously reported that in several renal cell types, adenosine receptor agonists inhibit adenylyl cyclase and activate phospholipase C via a pertussis toxin-sensitive G protein. In the present study, in 28A cells, both uf these adenosine receptor-mediated responses were inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). a highly selective A1 adenosine receptor antagonist. The binding characteristics of the adenosine A 1 receptor in the 28A renal cell line were studied using the radiolabeled antagonist f:1H]DPCPX to determine whether two separate binding sites could account for these responses. Saturation binding of [: 1H]DPCPX to 28A cell membranes revealed a single class of A1 binding sites with an apparent Kd value of 1.4 nM and maximal binding capacity of 64 fmol/mg protein. Competition experiments with a variety of adenosine agonists gave biphasic displacement curves with a pharmacological profile characteristic of A1 receptors. Comparison of [: 1H]DPCPX competition binding data from 28A cell membranes with rabbit brain membranes, a tissue with well-characterized A1 receptors, reveals that the A 1 receptor population in 28A cells has similar agonist binding affinities to the receptor population in brain but has a considerably lower density. Addition of guanosine ;)' -triphosphate ( 100 ,uM) to 28A cell membranes caused the competition curves to shift from biphasic to monophasic. indicating that the A1 receptors exist in two interconvertible affinity states because of their coupling to G proteins. In the absence of evidence for subpopulations of the A1 receptor, it appears that in 28A cells. A single A1 receptor population. As defined by ligand binding characteristics, couples via one or more pertussis toxin-sensitive guanine nucleotide binding proteins to two different biological signaling mechanisms. KW - calcium KW - phosphoinositides KW - adenosine 3',5'-cyclic monophosphate KW - receptor binding KW - signal transduction KW - G proteins Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86083 ER - TY - JOUR A1 - Koch, R. A1 - Deger, A. A1 - Klotz, Karl-Norbert A1 - Schenzle, D. A1 - Krämer, H. A1 - Kelm, S. A1 - Müller, G. A1 - Rapp, R. A1 - Weber, U. T1 - Characterization of solubilized insulin receptors from rat liver microsomes. Existence of two receptor species with different binding properties N2 - Insulin receptors were solubilized from rat liver microsomes by the nonionic detergent Triton X-100. After gel filtration of the extract on Sepharose CL-6B, two insulin-binding species (peak I and peak li) were obtained. The structure and binding properties of both peaks were characterized. Gel filtration yielded Stokes radii of 9.2 nm (peak I) and 8.0 nm (peak Il). Both peaks were glycoproteins. At 4°C peak 1 showed optimal insulin binding at pH 8.0 and high ionic strength. In contrast, peak li bad its binding optimum at pH 7.0 and low ionic strength, where peak I bindingwas minimal. For peak I the change in insulin binding under different conditions of pH and ionic strength was due to a change in receptor affinity only. For peak 11 an additional change in receptor number was found. Both peaks yielded non-linear Scatchard plots under most of the buffer conditions examined. At their binding optima at 4 oc the high affinity dissociation constants were 0.50 nM (peak I) and 0.55 nM (peak II). Sodium dodecyl sulfatejpolyacrylamide gel electrophoresis of peak I revealed five receptor bands with Mr 400000, 365000, 320000, 290000, and 245000 under non-reducing conditions. For peak II two major receptor bands with M\(_r\) 210000 and 115000 were found. The peak II receptor bands were also obtained aftermild reduction of peak I. After complete reduction both peaks showed one major receptor band with M\(_r\) 130000. The reductive generation of the peak II receptor together with molecular mass estimations suggest that the peak I receptor is the disulfide-linked dimer of the peak II receptor. Thus, Triton extracts from rat liver microsomes contain two receptor species, which are related, but differ considerably in their size and insulin-binding properties. KW - Toxikologie Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60215 ER - TY - JOUR A1 - Tawfik-Schlieper, H. A1 - Klotz, Karl-Norbert A1 - Kreye, V. A. W. A1 - Schwabe, U. T1 - Characterization of the K\(^+\)-channel-coupled adenosine receptor in guinea pig atria N2 - In the present work we studied the pharmacological profile of adenosine receptors in guinea pig atria by investigating the effect of different adenosine analogues on 86Rb + -efflux from isolated left atria and on binding of the antagonist radioligand 8-cyclopentyl-1 ,3-[\(^3\)H]dipropylxanthine ([\(^3\)H]DPCPX) to atrial membrane preparations. The rate of \8^{86}\)Rb\(^+\) -effiux was increased twofold by the maximally effective concentrations of adenosine receptor agonists. The EC50-values for 2-chloro-N\(^6\)-cyclopentyladenosine (CCPA), R-N\(^6\)-phenylisopropyladenosine (R-PIA), 5'-Nethylcarboxamidoadenosine (NECA), and S-N\(^6\)-phenylisopropyladenosine (S-PIA) were 0.10, 0.14, 0.24 and 12.9 \(\mu\)M, respectively. DPCPX shifted the R-PIA concentration-response curve to the right in a concentration-dependent manner with a K\(_B\)-value of 8.1 nM, indicating competitive antagonism. [\(^3\)H]DPCPX showed a saturable binding to atrial membranes with a Bmax·value of 227 fmol/mg protein and a K\(_D\)-value of 1.3 nM. Competition experiments showed a similar potency for the three agonists CCPA, R-PIA and NECA. S-PIA is 200 times less potent than R-PIA. Our results suggest that the K\(^+\) channel-coupled adenosine receptor in guinea pig atria is of an A\(_1\) subtype. KW - Toxikologie KW - A1 Adenosine receptors KW - K + -channels KW - Atria KW - Radioligand binding - 86Rb + -efflux Y1 - 1989 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60333 ER -