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, 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  - CHAP
A1  - Lohse, Martin J.
A1  - Klotz, Karl-Norbert
A1  - Schwabe, Ulrich
T1  - Functional characterization of A1 adenoosine receptors by photoaffinity labelling
N2  - The ligand-binding subunit ofthe A1 adenosine receptor has been identified in membranes with the photoaffinity Iabel R-2-azido-N6-p-hydroxyphenylisopropyladenosine (R-AHPIA). Covalent labelling ofthe A1 receptor can also be achieved in intact cells. The dissociation of the radioiodinated label (1251-AHPIA) from isolated rat fat cells was incomplete after UV irradiation, leaving about 20°/o of irreversible specific binding. Such covalent labelling of the receptor led to a concentration-dependent reduction of cellular cyclic AMP levels. This persistent effect of covalent labeHing occurred with an IC50 value of 9 nM, as compared to an IC50 value of 0.9 nM for the direct reduction of cyclic AMP Ievels by the ligand. The difference in the IC5o values can be explained by assuming spare receptors. This hypothesis was verified in binding studies using [ 3HJPIA as a radioligand. R-AHPIA inhibited binding of [3H)PIA to intact fat cells with a K1 value of about 20 nM, which is about 20 tim es high er than the corresponding IC50 value of cyclic AMP reduction. These data show that the A1 receptor is activated according to the occupancy theory. The high sensitivity of the activation in intact ceJis is due to a large number of spare receptors.
KW  - Adenosinrezeptor
Y1  - 1987
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-86097
ER  - 
TY  - JOUR
A1  - Lohse, M. J.
A1  - Elger, B.
A1  - Lindenborn-Fotinos, J.
A1  - Klotz, Karl-Norbert
A1  - Schwabe, U.
T1  - Separation of solubilized A\(_2\) adenosine receptors of human platelets from non-receptor [\(^3\)H]NECA binding sites by gel filtration
N2  - 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.
KW  - Toxikologie
KW  - A<sub>2</sub> Adenosine receptor
KW  - Human platelets
KW  - Radioligand binding
KW  - Adenylate cyclase
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60309
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  - 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  - 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  - Klotz, Karl-Norbert
A1  - Lohse, M. J.
A1  - Schwabe, U.
T1  - Chemical modification of A\(_1\) adenosine receptors in rat brain membranes - evidence for histidine in different domains of the ligand binding site
N2  - Chemical modification of amino acid residues was used to probe the ligand recognition site of A\(_1\) adenosine receptors from rat brain membranes. The effect of treatment with group·specific reagents on agonist and antagonist radioligand binding was investigated. The histidine-specific reagent diethylpyrocarbonate (DEP) induced a loss of binding of the agonist R-N\(^6\)-[\(^3\)H]phenylisopropyladenosine ([\(^3\)H]PIA), which could be prevented in part by agonists, but not by antagonists. DEP treatment induced also a loss of binding of the antagonist [\(^3\)H]8- cyclopentyl-1 ,3-dipropylxanthine ([\(^3\)H]DPCPX). Antagonists protected A\(_1\) receptors from this inactivation while agonists did not. This result provided evidence for the existence of at least 2 different histidine residues involved in ligand binding. Consistent with a modification of the binding site, DEP did not alter the affinity of [\(^3\)H]DPCPX, but reduced receptor number. From the selective protection of [\(^3\)H] PIA and [\(^3\)H]DPCPX binding from inactivation, it is concluded that agonists and antagonists oocupy different domains at the binding site. Sulfhydryl modifying reagents did not influence antagonist binding, but inhibited agonist binding. This effect is explained by modification of tbe inhibitory guanine nucleotide binding protein. Pyridoxal 5-phosphate inactivated both [\(^3\)H]PIA and [\(^3\)H]DPCPX binding, but the receptors could not be protected from inactivation by ligands. Therefore, no amino group seems to be located at the Iigand binding site. In addition, it was shown that no further amino acids witb polar side chains are present. The absence of bydrophilic amino acids frout the recognition site of the receptor apart from histidine suggests an explanation for the lack of hydrophilic ligands with high affinity for A\(_1\) receptors.
KW  - Toxikologie
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60295
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  - Reddington, M.
A1  - Klotz, Karl-Norbert
A1  - Lohse, M. J.
A1  - Hietel, B.
T1  - Radiation inactivation analysis of the A\(_1\) adenosine receptor: decrease in radiation inactivation size in the presence of guanine nucleotide
N2  - Radiation inactivation analysis of the binding of the A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine to rat brain membranes yielded a radiation inactivation size of 58 kDa. In the presence of GTPyS this was reduced to 33 kDa, in good agreement with the size of the ligand-binding subunit detected after photoaffinity labelling. The data indicate that the structural association of A\(_1\) adenosine receptors with G-protein components is altered in situ in the presence of guanine nucleotides.
KW  - Toxikologie
KW  - Adenosine receptor
KW  - A1
KW  - Radiation inactivation
KW  - Target size
KW  - G-protein
KW  - (Rat brain membrane)
Y1  - 1989
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-60318
ER  -