@article{LohseKlotzDiekmannetal.1988,
  author    = {Lohse, M. J. and Klotz, Karl-Norbert and Diekmann, E. and Friedrich, K. and Schwabe, U.},
  title     = {2',3'-Dideoxy-N\(^6\)-cyclohexyladenosine: an adenosine derivative with antagonist properties at adenosine receptors},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60282},
  year      = {1988},
  abstract  = {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.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{LohseKlotzSchwabeetal.1988,
  author    = {Lohse, M. J. and Klotz, Karl-Norbert and Schwabe, U. and Cristalli, G. and Vittori, S. and Grifantini, M.},
  title     = {2-Chloro-N\(^6\)-cyclopentyladenosine: a highly selective agonist at A\(_1\) adenosine receptors},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60279},
  year      = {1988},
  abstract  = {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.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{CristalliFranchettiGrifantinietal.1988,
  author    = {Cristalli, G. and Franchetti, P. and Grifantini, M. and Vittori, S. and Klotz, Karl-Norbert and Lohse, M. J.},
  title     = {Adenosine receptor agonists: Synthesis and biological evaluation of 1-deaza analogues of adenosine},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60262},
  year      = {1988},
  abstract  = {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.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{LohseElgerLindenbornFotinosetal.1988,
  author    = {Lohse, M. J. and Elger, B. and Lindenborn-Fotinos, J. and Klotz, Karl-Norbert and Schwabe, U.},
  title     = {Separation of solubilized A\(_2\) adenosine receptors of human platelets from non-receptor [\(^3\)H]NECA binding sites by gel filtration},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60309},
  year      = {1988},
  abstract  = {Human platelet membranes were solubilized with the zwitterionic detergent CHAPS (3-[3-(cholamidopropyl)dimethylammonio]- 1-propanesulfonate) and the solubilized extract subjected to gel ftltration. Binding of the adenosine receptor agonist [\(^3\)H]NECA (5'-N-ethylcarboxamidoadenosine) was measured to the eluted fractions. Two [\(^3\)H]NECA binding peaks were eluted, the first of them with the void volume. This first peak represented between 10\% and 25\% of the [\(^3\)H]NECA binding activity eluted from the column. It bound [\(^3\)H]NECA in a reversible, saturable and GTPdependent manner with an affinity of 46 nmol/1 and a binding capacity of 510 fmol/mg protein. Various adenosine receptor ligands competed for the binding of [\(^3\)H]NECA to the frrst peak with a pharmacological proftle characteristic for the A\(_2\) adenosine receptor as determined from adenylate cyclase experiments. In contrast, most adenosine receptor ligands did not compete for [\(^3\)H]NECA binding to the second, major peak. These results suggest that a solubilized A\(_2\) receptor-Gs protein complex of human platelets can be separated from other [\(^3\)H]NECA binding sites by gel filtration. This allows reliable radioligand binding studies of the A2 adenosine receptor of human plate1ets.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{LohseBoeserKlotzetal.1987,
  author    = {Lohse, M. J. and B{\"o}ser, S. and Klotz, Karl-Norbert and Schwabe, U.},
  title     = {Affinities of barbiturates for the GABA-receptor complex and A\(_1\) adenosine receptors: A possible explanation of their excitatory effects},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60250},
  year      = {1987},
  abstract  = {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.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{LohseKlotzLindenbornFotinosetal.1987,
  author    = {Lohse, M. J. and Klotz, Karl-Norbert and Lindenborn Fotinos, J. and Reddington, M. and Schwabe, U. and Olsson, R. A.},
  title     = {8-Cyclopentyl-1,3-dipropylxanthine (DPCPX) - a selective high affinity antagonist radioligand for A\(_1\) adenosine receptors},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60246},
  year      = {1987},
  abstract  = {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.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{KlotzLohse1986,
  author    = {Klotz, Karl-Norbert and Lohse, M. J.},
  title     = {The glycoprotein nature of A\(_1\) adenosine receptors},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60231},
  year      = {1986},
  abstract  = {A\(_1\) adenosine receptors from different tissues and species we~e photoaffinity labelled and then the carbohydrate content was examined by both enzymatic and chemical treatment. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the labelled membrane receptors shows that neuraminidase treatment alters the electrophoretic mobility of the receptor band indica ting the presence of terminal neurandnie acids. Neuraminidase digestion does not influence the binding characteristics of the receptor. The totally deglycosylated receptor protein obtained by chemical treatment has an apparent molecular weight Of 32,000.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{KlotzLohseSchwabe1986,
  author    = {Klotz, Karl-Norbert and Lohse, M. J. and Schwabe, U.},
  title     = {Characterization of the solubilized A\(_1\) adenosine receptor from rat brain membranes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60222},
  year      = {1986},
  abstract  = {A\(_1\) adenosine receptors from rat brain membranes were solubilized with the zwitterionic detergent 3-[3-( cholamidopropyl)dimethylammonio]-1-propanesulfonate. The solubilized receptors retained all the characteristics of membrane-bound A\(_1\) adenosine receptors. A high and a low agonist affinity state for the radiolabelled agonist (R)-\(N^6\)-[\(^3\)H]phenylisopropyladenosine([\(^3\)H]PJA) with K\(_D\) values of 0.3 and 12 nM, respectively, were detected. High-affinity agonist binding was regulated by guanine nucleotides. In addition agonist binding was still modulated by divalent cations. The solubilized A\(_1\) adenosine receptors could be labelled not only with the agonist [\(^3\)H]PIA but also with the antagonist I ,3-diethyi-8-[\(^3\)H]phenylxanthine. Guanine nucleotides did not affect antagonist binding as reported for membrane-bound receptors. These results suggest that the solubilized receptors are still coupled to the guanine nucleotide binding protein N; and that all regulatory functions are retained on solubilization. Key Words: A1 adenosine receptors - Solubilization- Rat brain membranes. Klotz K.-N. et al. Characterization of the solubilized A1 adenosine receptor from rat brain membranes. J. Neurochem. 46, 1528-1534 (1986).},
  subject      = {Toxikologie},
  language  = {en}
}
@article{KochDegerKlotzetal.1986,
  author    = {Koch, R. and Deger, A. and Klotz, Karl-Norbert and Schenzle, D. and Kr{\"a}mer, H. and Kelm, S. and M{\"u}ller, G. and Rapp, R. and Weber, U.},
  title     = {Characterization of solubilized insulin receptors from rat liver microsomes. Existence of two receptor species with different binding properties},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60215},
  year      = {1986},
  abstract  = {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.},
  subject      = {Toxikologie},
  language  = {en}
}
@article{UkenaSchirrenKlotzetal.1985,
  author    = {Ukena, D. and Schirren, C. G. and Klotz, Karl-Norbert and Schwabe, U.},
  title     = {Evidence for an A\(_2\) adenosine receptor in guinea pig lung},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60202},
  year      = {1985},
  abstract  = {Adenosine receptors in guinea pig lung were characterized by measurement of cyclic AMP formation and radioligand binding. 5'-N-Ethylcarboxamidoadenosine (NECA) increased cyclic AMP Ievels in lung slices about 4-fold over basal values with an EC\(_{50}\) of 0.32 \(\mu\)mol/l. N\(^6\) - R-(- )-Phenylisopropyladenosine (R-PIA) was 5-fold less potent than NECA. 5'-N-Methylcarboxamidoadenosine (MECA) and 2-chloroadenosine had EC\(_{50}\)-values of 0.29 and 2.6 \(\mu\)mol/l, whereas adenosine and inosine had no effect. The adenosine receptors in guinea pig Iung can therefore be classified as A\(_2\) receptors. Several xanthine derivatives antagonized the NECA-induced increase in cyclic AMP levels. 1,3-Diethyl-8-phenylxanthine (DPX; K\(_i\) 0.14 \(\mu\)mol/l) was the most potent analogue, followed by 8-phenyltheophylline (K\(_i\) 0.55 \(\mu\)mol/l), 3-isobutyl-1-methylxanthine (IBMX; K\(_i\) 2.9 \(\mu\)mol/l) and theophylline (K\(_i\) 8.1 \(\mu\)mol/l). In contrast, enprofylline (1 mmol/1) enhanced basal and NECA-stimulated cyclic AMP formation. In addition, we attempted to characterize these receptors in binding studies with [\(^3\)H]NECA. The K\(_D\) for [\(^3\)H] NECA was 0.25 \(\mu\)mol/l and the maximal number of binding sites was 12 pmol/mg protein. In competition experiments MECA (K\(_i\) 0.14 \(\mu\)mol/l) was the most potent inhibitor of [\(^3\)H] NECA binding, followed by NECA (K\(_i\) 0.19 \(\mu\)mol/l) and 2-chloroadenosine (K\(_i\) 1.4 \(\mu\)mol/l). These results correlate well with the EC\(_{50}\)- values for cyclic AMP formation in lung slices. However, the K\(_i\)-values of R-PIA and theophylline were 240 and 270 \(\mu\)mol/l, and DPX and 8-phenyltheophylline did not compete for [\(^3\)H]NECA binding sites. Therefore, a complete characterization of A\(_2\) adenosine receptors by [\(^3\)H] NECA binding was not achieved. In conclusion, our results show the presence of adenylate cyclase-coupled A\(_2\) adenosiile receptors in lung tissue which are antagonized by several xanthines.},
  subject      = {Toxikologie},
  language  = {en}
}