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S Wurster

Publications and source records attributed to S Wurster.

14 recordsLinked to original sources
PubMed2003

Identification and characterization of the imidazoline I2b-binding sites in the hamster brown adipose tissue as a study model for imidazoline receptors.

The imidazoline-type compound, MPV-1743, has been found to activate nonshivering thermogenesis (NST) in brown adipose tissue (BAT) of the genetically obese Zucker rats. The regulation of NST in BAT is linked to the catecholamine metabolism, and the imidazoline I2-binding sites have been found on the monoamine oxidase, a catecholamine metabolising enzyme. In this study, the I2-binding sites of hamster BAT have been characterised using a receptor binding assay with 3H-idazoxan as a radioligand, and the interaction of MPV-1743 with these I2-binding sites has been studied using the enantiomers of MPV 1743, that is, MPV 2088 and MPV 2089. Cirazoline was used to determine the specific binding of 3H-idazoxan to the imidazoline I2-binding sites. Rauwolscine was added in the 3H-idazoxan binding assay in order to inhibit any binding to potential alpha2-adrenergic sites. In the presence of rauwolscine mask 3H-Idazoxan labelled a population of non-adrenergic binding sites expressing the properties of the imidazoline I2b-receptor subtype similar to that found in the rat liver (cirazoline >> guanabenz = amiloride >> clonidine). The binding of 3H-idazoxan to the I2b-binding sites could be displaced by the imidazole compounds with the following affinities: detomidine (KiHigh 9.2 nM; KiLow 3200 nM), MPV-2088 (KiHigh 19 nM; IKiLow 760 nM) and MPV-2089 (KiHigh 190 nM; KiLow 1300 nM), atipamezole (3500 nM) and dexmedetomidine (Ki 8400 nM). These results have shown that the hamster BAT contains the imidazoline I2b-binding sites with heterogeneous binding properties for some test compounds. In addition, the enantiomers of MPV 1743, that is, MPV 2088 and MPV 2089, had high affinity to these BAT imidazoline I2b-binding sites. Therefore, it is suggested that the regulation of NST in the hamster BAT may be an attractive model to study the role of imidazoline I2b-binding sites.

Adipose Tissue, Brown↗
PubMed2001

Molecular mechanism for agonist-promoted alpha(2A)-adrenoceptor activation by norepinephrine and epinephrine.

We present a mechanism for agonist-promoted alpha(2A)-adrenergic receptor (alpha(2A)-AR) activation based on structural, pharmacological, and theoretical evidence of the interactions between phenethylamine ligands and alpha(2A)-AR. In this study, we have: 1) isolated enantiomerically pure phenethylamines that differ both in their chirality about the beta-carbon, and in the presence/absence of one or more hydroxyl groups: the beta-OH and the catecholic meta- and para-OH groups; 2) used [(3)H]UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine; agonist] and [(3)H]RX821002 [2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline; antagonist] competition binding assays to determine binding affinities of these ligands to the high- and low-affinity forms of alpha(2A)-AR; 3) tested the ability of the ligands to promote receptor activation by measuring agonist-induced stimulation of [(35)S]GTPgammaS binding in isolated cell membranes; and 4) used automated docking methods and our alpha(2A)-AR model to predict the binding modes of the ligands inside the alpha(2A)-AR binding site. The ligand molecules are sequentially missing different functional groups, and we have correlated the structural features of the ligands and ligand-receptor interactions with experimental ligand binding and receptor activation data. Based on the analysis, we show that structural rearrangements in transmembrane helix (TM) 5 could take place upon binding and subsequent activation of alpha(2A)-AR by phenethylamine agonists. We suggest that the following residues are important in phenethylamine interactions with alpha(2A)-AR: Asp113 (D(3.32)), Val114 (V(3.33)), and Thr118 (T(3.37)) in TM3; Ser200 (S(5.42)), Cys201 (C(5.43)), and Ser204 (S(5.46)) in TM5; Phe391 (F(6.52)) and Tyr394 (Y(6.55)) in TM6; and Phe411 (F(7.38)) and Phe412 (F(7.39)) in TM7.

Adrenergic Agonists↗
PubMed1999

Alpha2-adrenoceptor agonists stimulate high-affinity GTPase activity in a receptor subtype-selective manner.

Transfected Chinese hamster ovary cells expressing human alpha2A-, alpha2B- and alpha2C-adrenoceptor subtypes were used to monitor alpha2-adrenoceptor-stimulated GTP hydrolysis. Incubation with 100 microM (-)-adrenaline resulted in stimulation of pertussis toxin-sensitive GTPase by 380% after activation of the alpha2A-subtype, by 320% after activation of the alpha2B-subtype and by 110% after activation of the alpha2C-subtype. The agonists dexmedetomidine, UK14,304 (5-bromo-6-[2-imidazoline-2-ylamino]quinoxaline) and oxymetazoline showed subtype-dependent efficacy. Dexmedetomidine was a full agonist at the alpha2B-subtype and a partial agonist at the alpha2A- and the alpha2C-subtypes. UK14,304 was a full agonist at the alpha2A-subtype and a partial agonist at the other two. Oxymetazoline showed strong partial agonism at the alpha2B-subtype (63% of adrenaline), but did not significantly activate the alpha2A- and the alpha2C-subtypes. These results agreed with cAMP accumulation experiments carried out with cell lines endogenously expressing the alpha2A-subtype (human erythroleukemia, HEL) or the alpha2B-subtype (neuroblastoma-glioma, NG108-15). The GTPase assay may thus provide a valuable tool for the identification of subtype-selective alpha2-adrenoceptor agonists.

Adrenergic alpha-2 Receptor Agonists↗
PubMed1998

Modulation of agonist binding to recombinant human alpha2-adrenoceptors by sodium ions.

Agonist binding to alpha2-adrenoceptors is modulated by a number of factors such as Mg2+ and Na+ ions and by experimental manipulations which interfere with receptor-G-protein-coupling such as pertussis toxin pre-treatment or the presence of guanine nucleotides. Agonist binding assays may therefore offer an opportunity to make inferences, albeit indirect, about receptor states or conformations and about the molecular nature of the processes involved in receptor activation. We have investigated possible differences in the effects of Na+ ions on the binding of agonists to the three human alpha2-adrenoceptor subtypes, alpha2A, alpha2B and alpha2C, recombinantly expressed in S115 mouse mammary tumour cells. NaCl (40 mM) influenced the apparent affinity of a panel of alpha2-adrenoceptor ligands in a complex compound- and subtype-dependent manner. Sodium ions affected both high- and low-affinity conformations of the receptors, as defined by co-incubation with 10 microM 5'-guanylylimidodiphosphate (Gpp(NH)p). The effects of NaCl and Gpp(NH)p on agonist binding were additive indicating different modes of action for the two allosteric modulators. Thus, quite marked differences between closely related receptor subtypes were noted in the molecular details of agonist-receptor interactions and in the integration of allosteric modulation by Na+ ions. Possible explanations for the experimental findings are discussed within the theoretical framework of multi-state models, and a proposal is presented for a potential physiological role of the modulatory effect of Na+ ions, where intracellular Na+ concentrations would direct the activating influence of receptors to different G-proteins.

Adrenergic alpha-Agonists↗
PubMed1998

[Explant test with skin and peritoneum of the neonatal rat as a predictive test of tolerance of local anti-infective agents in wounds and body cavities].

In vitro culture of peritoneal explants of neonatal rats after previous application of agents simulating wound antisepsis is a sensitive screening method for the determination of the tissue compatibility of local wound antiinfectives. Two test models are differentiated: (1) separated peritoneal explants as a model for chronic or deep wounds and (2) peritoneum in situ in the experimental animal with subsequent extraction and cultivation of the explants. Considering the present state of knowledge the following conclusions can be drawn regarding antisepsis of wounds: Lavasept (0.1%) may be classified as the agent of choice for deep and chronic wounds, for drip-suck irrigation and for antiinfective lavage of body cavities inclusively for peritoneal lavage (0.05%). Taurolidin is antiseptically effective in long term application (> 6 h), and because of its antitoxic effect as well as lack of cytotoxicity it is especially suitable for peritoneal lavage. Betaisodona solution is very well suited for superficial contaminated wounds and can be used in a dilution of 1:10 for short-term rinsing of deep wounds, including body cavities but not for peritoneal lavage. Ethanol causes no inhibition of explant growth and therefore retains its importance in wound antisepsis.

Administration, Topical↗
PubMed1998

Protean agonism at alpha2A-adrenoceptors.

The coupling of the endogenously expressed alpha2A-adrenoceptors in human erythroleukemia cells (HEL 92.1.7) to Ca2+ mobilization and inhibition of forskolin-stimulated cAMP production was investigated. The two enantiomers of medetomidine [(+/-)-[4-(1-[2, 3-dimethylphenyl]ethyl)-1H-imidazole]HCl] produced opposite responses. Dexmedetomidine behaved as an agonist in both assays (i.e. , it caused Ca2+ mobilization and depressed forskolin-stimulated cAMP production). Levomedetomidine, which is a weak agonist in some test systems, reduced intracellular Ca2+ levels and further increased forskolin-stimulated cAMP production and therefore can be classified as an inverse agonist. A neutral ligand, MPV-2088, antagonized responses to both ligands. Several other, chemically diverse alpha2-adrenergic ligands also were tested. Ligands that could promote increases in Ca2+ levels and inhibition of cAMP production could be classified as full or partial agonists. Their effects could be blocked by the alpha2-adrenoceptor antagonist rauwolscine and by pertussis toxin treatment. Some typical antagonists such as rauwolscine, idazoxan, and atipamezole had inverse agonist activity like levomedetomidine. The results suggest that the alpha2A-adrenoceptors in HEL 92.1.7 cells exist in a precoupled state with pertussis toxin-sensitive G proteins, resulting in a constitutive mobilization of intracellular Ca2+ and inhibition of cAMP production in the absence of agonist. This constitutive activity can be antagonized by inverse agonists such as levomedetomidine and rauwolscine. Levomedetomidine can be termed a "protean agonist" because it is capable of activating uncoupled alpha2-adrenoceptors in other systems and inhibiting the constitutive activity of precoupled alpha2-adrenoceptors in HEL 92.1. 7 cells. With this class of compounds, the inherent receptor "tone" could be adjusted, which should provide a new therapeutic principle in receptor dysfunction.

Adrenergic alpha-Agonists↗
PubMed1997

Different apparent modes of inhibition of alpha2A-adrenoceptor by alpha2-adrenoceptor antagonists.

The inhibition of alpha2A-adrenoceptor-mediated Ca2+ elevation by alpha2-adrenoceptor antagonists was measured in HEL human erythroleukemia cells. The antagonists could be divided in two classes: those that displayed surmountable inhibition (right-shift of the agonist dose-response curve), and those that displayed different degrees of insurmountable inhibition (depression of the maximum signal and a possible right-shift of the agonist dose-response curve). The degree of surmountability of the inhibition correlated well with the measured antagonist dissociation rates, suggesting that the hypothesis of the antagonist dissociation rate governing the mode of inhibition of fast responses, holds true. HEL cells thus provide a useful model system for the investigation of physiological consequences of different dissociation rates. Also, the dissociation rates of antagonists not available in radiolabelled form can be predicted from the functional data. The data stresses the importance of measurement of kinetic parameters of the drug-receptor interaction in addition to the equilibrium binding constants.

Adrenergic alpha-2 Receptor Antagonists↗
PubMed1994

The voltage-sensitive Ca2+ channel (VSCC) antagonists omega-Aga-IVA and omega-CTX-MVIIC inhibit spontaneous epileptiform discharges in the rat cortical wedge.

The ability of VSCC antagonists to modulate excitatory amino acid (EAA) release was evaluated by measuring N-methyl-D-aspartate (NMDA) receptor-dependent spontaneous epileptiform discharges in rat cortical wedges. The N-type channel blocker omega-CTX-GVIA (300 nM) was ineffective. The P-type channel blocker omega-Aga-IVA at 300 nM reduced the frequency of discharges by 63%, while 300 nM omega-CTX-MVIIC reduced the frequency by 35%. These results coupled with the absence of NMDA antagonism by omega-Aga-IVA or omega-CTX-MVIIC in the cortical wedge suggest that the VSCCs blocked by these toxins are primarily responsible for mediating impulse dependent EAA release in the rat neocortex.

Animals↗
PubMed1991

Effect of fluoride, pertussis and cholera toxin on the release of arachidonic acid and the formation of prostaglandin E2, D2, superoxide and inositol phosphates in rat liver macrophages.

Fluoride elicited in liver macrophages a release of arachidonic acid and prostaglandins but not formation of inositol phosphates or superoxide. The effects of fluoride required extracellular calcium and were inhibited by staurosporine and by phorbol ester treatment of the cells. Furthermore, fluoride led to a translocation of protein kinase C from the cytosol to membranes. This indicates that the calcium-dependent protein kinase C is involved in the action of fluoride. Cholera toxin decreased the zymosan-induced release of arachidonic acid and prostaglandins but not of inositol phosphates or superoxide. Pertussis toxin ADP-ribosylated a 41,000 molecular weight membrane protein; enhanced specifically the zymosan-induced formation of prostaglandin(PG)E2 but did not affect the zymosan-induced release of arachidonic acid, PGD2, inositol phosphates or superoxide. These data suggest that activation of phospholipase (PL)A2, phosphoinositide (PI)-specific PLC and NADPH oxidase in liver macrophages is most probably not mediated by activation of guanine nucleotide binding (G)-proteins coupled directly to these enzymes.

Adenosine Diphosphate Ribose↗
PubMed1990

Regulatory proteins in presynaptic function.

Activation of alpha 2-adrenoceptors, opioid, A1-adenosine, and PGE receptors inhibited the stimulation-induced [3H]noradrenaline release in brain tissue in a concentration-dependent manner. Under experimental conditions (360 pulses/3 Hz) where the released noradrenaline activated the presynaptic alpha 2-autoreceptors, the effects of the heteroreceptor (k-opioid, A1-adenosine, PGE) agonists were decreased. By avoiding autoinhibition by either blockade of the alpha 2-autoreceptors with yohimbine or stimulating the tissue with four pulses/100 Hz, the heteroreceptor-mediated inhibition of [3H]noradrenaline release was markedly increased. The dependence of the heteroreceptor-mediated inhibition of evoked noradrenaline release on the extent of alpha 2-autoreceptor activation suggests a common postreceptor signal transduction pathway. PTX-catalyzed [32P]ADP ribosylation of synaptosomal membrane proteins revealed three bands of polypeptides with molecular weights corresponding to the alpha subunits of Go (39,000) and the Gi proteins (40,000, 41,000). Pretreatment with NEM reduced the PTX-induced 32P labeling by alkylating the alpha subunits at or near the site that is ADP ribosylated by PTX in a concentration-dependent manner. K(+)-evoked release of [3H]noradrenaline from synaptosomes indicated the presynaptic localization of the PTX-sensitive G proteins coupled to alpha 2-, k-, and A1-receptors of noradrenergic nerve terminals. Electrically evoked [3H]noradrenaline release was only increased by PTX or NEM in a time- and concentration-dependent manner when autoinhibition was present. The alpha 2-, opioid, and A1-adenosine receptor-mediated inhibition of [3H]noradrenaline release was impaired similarly by PTX or NEM treatment. In contrast, the inhibitory effect of PGE2 remained unaffected. These results indicate that presynaptic alpha 2-, opioid, and A1-receptors but not PGE receptors of noradrenergic nerve terminals are linked to PTX-sensitive G proteins. The interaction between the alpha 2-autoreceptors and the PGE receptors therefore does not occur at the level of a common pool of G proteins but at some subsequent step of the signal transduction mechanism.

Animals↗
PubMed1989

Effects of botulinum A toxin on presynaptic modulation of evoked transmitter release.

A possible influence of botulinum A toxin on the modulation of evoked neurotransmitter release was investigated in hippocampus tissue. Rabbit hippocampal slices prelabelled with [3H]noradrenaline ([3H]NA), [3H]5-hydroxytryptamine ([3H]5-HT) or [3H]choline were superfused with physiological medium and were stimulated electrically during superfusion. The evoked release of [3H]NA, [3H]5-HT and [3H]acetylcholine [( 3H]ACh) was inhibited by botulinum A toxin in a concentration- and time-dependent manner. Neither the inhibition of release of [3H]NA and [3H]5-HT by the alpha 2-adrenoceptor agonist clonidine nor facilitation of release in the presence of alpha 2-antagonists were influenced by pretreatment of the tissue with botulinum toxin. The toxin caused no [32P]ADP ribosylation of synaptosomal proteins of hippocampus. The facilitation of the stimulation-induced [3H]NA and [3H]5-HT release by the specific protein kinase C (PKC) activator 4 beta-phorbol-12,13-dibutyrate (PDB) was significantly diminished by botulinum A toxin. These results show that the evoked transmitter release is inhibited by botulinum A toxin by a mechanism which does not involve ADP ribosylation or an interaction with the alpha 2-adrenoceptor mechanism.

Acetylcholine↗
PubMed1988

P2-purinoceptor induced prostaglandin synthesis in primary rat astrocyte cultures.

Adenosine triphosphate (ATP) is one of the cotransmitters that are commonly released at catecholaminergic and cholinergic nerve terminals. The glial cell type most closely associated with the synapse is the astrocyte and, thus, is the next cellular element beside the postsynaptic neuron to face the transmitters released. This report gives evidence of P2-purinoceptors on cultured astroglial cells. Upon stimulation with nucleoside triphosphates and nucleoside diphosphates, the cells respond with synthesis of prostaglandins of the D2 type, which is the predominant prostaglandin made in rat brain. Nucleoside triphosphate analogues, such as 5'-adenyl-imido diphosphate, beta,gamma-methylene, or alpha,beta-methylene ATP were less effective than ATP or its non-hydrolysable analogue ATP [gamma S]. The receptor was desensitized by ATP [gamma S] within 15 min, whereas desensitization by alpha,beta-methylene ATP was significantly delayed. 8-phenyl-theophylline (10(-4) M) had no influence on ATP-stimulated prostaglandin synthesis. Adenosine 5'-monophosphate (AMP) and adenosine were unable to stimulate prostaglandin D2 formation. According to the common nomenclature for purinoceptors, the described astroglial receptor would fulfill the characteristics of a P2-purinoceptor. Furthermore, it is shown that pertussis toxin sensitive G-proteins influence some early step in prostaglandin synthesis. The inactivation of these proteins results in reduced prostaglandin formation. It is assumed that ATP serves as an important mediator in the cross-talk between neurons and astroglial cells at the synaptic cleft.

Adenosine Triphosphate↗
PubMed1988

Multiple pertussis toxin substrates as candidates for regulatory G proteins of adenylate cyclase coupled to the somatostatin receptor in primary rat astrocytes.

The involvement of G proteins in receptor mediated astroglial cAMP formation was studied. Isoproterenol or prostaglandin E2 stimulated adenylate cyclase of primary astroglial cells was inhibited by somatostatin. Preincubation of cells with increasing concentrations of islet activating protein (IAP) diminished somatostatin inhibition of adenylate cyclase. At an IAP concentration of 50 ng/ml somatostatin inhibition was completely abolished. Studies on IAP catalyzed 32P-ADP-ribosylation of astroglial cell particulate material revealed an incorporation of radiolabel into three polypeptides in the molecular weight range of 41,000-39,000 Dalton. Pretreatment of intact cells with IAP reduced radiolabeling of this molecular species in a concentration dependent manner. No further radiolabeling above background level was detectable after pretreatment of cultures with 10 ng IAP/ml or more. At present, the occurrence of at least three IAP substrates (G proteins) does not permit an identification of the somatostatin receptor coupled G protein. Rather, the finding reveals that astrocytes are endowed with multiple variants of GTP binding proteins likely to be coupled to different receptors.

Adenylate Cyclase Toxin↗