@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{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{LohseMaurerKlotzetal.1989, author = {Lohse, M. J. and Maurer, K. and Klotz, Karl-Norbert and Schwabe, U.}, title = {Synergistic effects of calcium-mobilizing agents and adenosine on histamine release from rat peritoneal mast cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60346}, year = {1989}, abstract = {1 Adenosine and its metabolically stable analogue N.etbyl-carboxamidoadenosine (NECA) enhance histamine release from rat peritoneal mast cells when tbese are stimulated by calciummobilizing agents. NECA and adenosine shift the concentration-response curve of tbe calcium ionophore A23187 to lower concentrations. 2 The potencies of NECA or adenosinein enhancing A23187-induced histamine release are dependent on the Ievel of stimulated release in tbe absence of adenosine analogues. At high Ievels of release their potencies are up to 20 times higher than at low Ievels. Consequently, averaged concentration-response curves of adenosine and NECA for enhancing bistamine release are shallow. 3 The adenosine transport blocker S-(p-nitrobenzyl)-6-thioinosine (NBTI) has no effect by itself at low Ievels of stimulated histamine release, but abolishes the enhancing effect of adenosine. At high Ievels of release, however, NBTI alone enhances the release of histamine. 4 lt is concluded that adenosine and calcium reciprocally enhance the sensitivity of the secretory processes to the effects of the other agent. The Ievels of intracellular adenosine obtained by trapping adenosine inside stimulated mast cells are sufficient to enhance histamine release substantially, suggesting that this effect may play a physiological and pathophysiological role.}, subject = {Toxikologie}, language = {en} } @incollection{LohseKlotzMaureretal.1990, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Maurer, K. and Ott, I. and Schwabe, Ulrich}, title = {Effects of adenosine on mast cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86101}, publisher = {Universit{\"a}t W{\"u}rzburg}, year = {1990}, abstract = {No abstract available}, subject = {Adenosin}, language = {en} } @article{LohseKlotzSalzeretal.1988, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Salzer, Manfred J. and Schwabe, Ulrich}, title = {Adenosine regulates the \(Ca^{2+} \) sensitivity of mast cell mediator release : (histamine secretion/inositol phosphates/calcium)}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {85}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-127883}, pages = {8875-8879}, year = {1988}, abstract = {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.}, language = {en} } @article{LohseKlotzSchwabe1991, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Schwabe, Ulrich}, title = {Mechanism of A2 adenosine receptor activation. I. Blockade of A2 adenosine receptors by photoaffinity labeling}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86073}, year = {1991}, abstract = {It has previously been shown that covalent incorporation of the photoreactive adenosine derivative (R)-2-azido-N6-p-hydroxyphenytisopropyladenosine [(R)-AHPIA] into the A, adenosine receptor of intact fat cells leads to a persistent activation of this receptor, resulting in a reduction of celular cAMP Ieveis [Mol. Pharmacol. 30:403-409 (1986)]. In contrast, covalent incorporation of (R)-AHPIA into human platelet membranes, which contain only stimulatory A2 adenosine receptors, reduces adenytate cyclase Stimulation via these receptors. This effect of (R)-AHPIA is specific for the A2 receptor and can be prevented by the adenosine receptor antagonist theophylline. Binding studies in-dicate that up to 90\% of A2 receptors can be blocked by photoincorporation of (R)-AHPIA. However, the remaining 10-20\% of A2 receptors are sufficient to mediate an adenylate cyclase Stimulation of up to SOOk of the control value. Similarly, the activation via these 10-20\% of receptors occurs with a halflife that is only 2 times Ionger than that in control membranes. This indicates the presence of a receptor reserve, with respect to both the extent and the rate of adenytate cyclase Stimulation. These observations require a modification of the models of receptor-adenytate cyclase coupling, which is described in the accompanying paper [Mol. Pharmacol. 39:524-530 (1991)].}, subject = {Adenosinrezeptor}, language = {en} } @incollection{LohseKlotzSchwabe1985, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Schwabe, Ulrich}, title = {Effects of barbiturates on A1 adenosine receptors of rat brain}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-70100}, publisher = {Universit{\"a}t W{\"u}rzburg}, year = {1985}, abstract = {Barbiturates inhibit binding of radioligands to A 1(Ri) adenosine receptors of rat brain membranes. This inhibition is dose-dependent and stereospecific and occurs in the range of pharmacologically active concentrations. The displacement of radiolabelled A1antagonists by barbiturates is not modified by GTP, indicating that barbiturates might act as antagonists at this receptor. This action of barbiturates does not seem to be related to the binding of barbiturates to plasma membranes, as the latter process has different characteristics. Barbiturates also inhibit the binding of radioligands to solubilized A1receptors, and saturation and kinetic experiments suggest that this is due to a competitive antagonism. These results indicate that barbiturates interact with the recognition site of the A1adenosine receptor.}, subject = {Barbiturat}, language = {en} } @incollection{LohseKlotzSchwabe1987, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Schwabe, Ulrich}, title = {Functional characterization of A1 adenoosine receptors by photoaffinity labelling}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86097}, publisher = {Universit{\"a}t W{\"u}rzburg}, year = {1987}, abstract = {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.}, subject = {Adenosinrezeptor}, language = {en} } @article{LohseKlotzSchwabe1986, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Schwabe, Ulrich}, title = {Effectes of temperature and membrane phase transitions on ligand binding to a2-receptors of human platelets}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86023}, year = {1986}, abstract = {The binding of agonists and antagonists to a2-adrenergic receptors of human platelets was studied. The receptors showed homogeneaus affinities for antagonists but two affinity states for the agonist (-)-epinephrine, which were modulated by guanine nucleotides. Van't Hoffplots of antagonist binding had a break point at about 18° and considerable diversity between 18° and 0°. Agonist binding to both affinity states showed a similar break point; agonist binding to the high affinity state was characterized by a large entropy component compared to the low affinity state. This entropy component was reduced at higher concentrations of sodium, indicating that it may be due to Iiberation of sodium ions. Measurements of the fluorescence of 1-anilin-8-naphthalenesulfonate showed thermotropic phase transitions of theplatelet membranes at about 17°. The transition temperature was decreased to about 12° by addition of 1 0 mM octanoic acid. Octanoic acidalso shifted the break points of the van't Hoffplot of antagonist and low affinity agonist binding from 18° to 12°. High affinity agonist binding, however, remained unchanged. It is concluded that agonist-specific thennodynamic characteristics of ligand binding to a2-receptors of human platelets can only be investigated by regarding differences between high and low affinity agonist binding. These differences include an entropy increase upon Iigand binding, which is in part due to enhanced liberation of sodium ions, and a loss of sensitivity to fluidity changes in the outer layer of the plasma membrane.}, subject = {Molekularpharmakologie}, language = {en} } @article{LohseKlotzSchwabe1986, author = {Lohse, Martin J. and Klotz, Karl-Norbert and Schwabe, Ulrich}, title = {Agonist photoaffinity labeling of A1 adenosine receptors: Persistent activation reveals spare receptors}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-87966}, year = {1986}, abstract = {No abstract available.}, subject = {Pharmazie}, language = {en} }