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G Lambrecht

Publications and source records attributed to G Lambrecht.

At least 19 recordsLinked to original sources
PubMed2003

Characterization of muscarinic autoreceptors in the rabbit hippocampus and caudate nucleus.

Oxotremorine-induced inhibition of electrically evoked release of 3H-acetylcholine from brain slices preincubated with 3H-choline was used to characterize muscarinic autoreceptors in rabbit hippocampus and caudate nucleus. From the shifts to the right of the concentration-response curves of oxotremorine in the presence of muscarinic receptor antagonists, the following pKB values [95% C.I.] were determined in the hippocampus: tripinamide: 8.7 [8.5, 8.8]; himbacine: 8.4 [8.3, 8.5]; AQ-RA 741: 8.3 [8.2, 8.5]; 4-DAMP: 8.2 [8.0, 8.3]; hexahydrosiladifenidol: 7.4 [7.2, 7.5]; AF-DX 116: 7.3 [7.1, 7.4]; pirenzepine: 6.8 [6.6, 7.0]; and PD102807: 6.3 [6.0, 6.5]. In the caudate nucleus: tripinamide: 9.1 [8.9, 9.2]; 4-DAMP: 8.3 [8.2, 8.5]; himbacine: 8.1 [8.0, 8.2]; AQ-RA 741: 8.1 [8.0, 8.3]; hexahydrosiladifenidol: 7.3 [7.2, 7.4]; AF-DX 116: 7.1 [7.0, 7.2]; pirenzepine: 6.7 [6.6, 6.8]; and PD102807: 6.5 [6.2, 6.8]. These pKB values fit best to literature values for M2 receptors, suggesting that the muscarinic autoreceptor of the rabbit hippocampus and caudate nucleus is the m2 gene product.

Acetylcholine↗
PubMed2001

Design and pharmacology of quinuclidine derivatives as M2-selective muscarinic receptor ligands.

In our search for M2-selective muscarinic receptor antagonists, we synthesized 1,3-disubstituted indenes. The effects of different basic moieties with regard to binding and selectivity towards the five distinct muscarinic receptor subtypes were investigated. The results show that the quinuclidine series afforded the most promising compounds in terms of both receptor affinity and M2-subtype selectivity.

Alzheimer Disease↗
PubMed2001

NF449: a subnanomolar potency antagonist at recombinant rat P2X1 receptors.

Antagonistic effects of the novel suramin analogue 4,4',4",4"'-(carbonylbis(imino-5,1,3-benzenetriylbis(carbonylimino)))tetrakis-benzene-1,3-disulfonic acid (NF449) were studied on contractions of the rat vas deferens elicited by alpha,beta-methylene ATP (alphabetameATP; mediated by P2X1 receptors), contractions of the guinea-pig ileal longitudinal smooth muscle elicited by alphabetameATP (mediated by P2X3 receptors) or adenosine 5'-O-(2-thiodiphosphate) (ADPbetaS; mediated by P2Y1 receptors), ATP-induced increases of [Ca2+]i in human embryonic kidney (HEK) 293 cells (mediated by P2Y2 receptors), inward currents evoked by ATP in follicle cell-free Xenopus laevis oocytes expressing rP2X1 or rP2X3 receptors and degradation of ATP by ecto-nucleotidases in folliculated Xenopus laevis oocytes. In addition, NF449 was examined for its P2 receptor specificity in rat vas deferens (alpha1A-adrenoceptors) and guinea-pig ileum (histamine H1 and muscarinic M3 receptors). At native (pIC50=7.15) and recombinant (pIC50=9.54) P2X1 receptors, NF449 was a highly potent antagonist. The P2X3 receptors present in guinea-pig ileum (pIC50=5.04) or expressed in oocytes (pIC50 approximately 5.6) were much less sensitive for NF449. It also was a very weak antagonist at P2Y1 receptors in guinea-pig ileum (pIC50=4.85) and P2Y2 receptors in HEK 293 cells (pIC50=3.86), and showed very low inhibitory potency on ecto-nucleotidases (pIC50<3.5). NF449 (100 microM) did not interact with alpha1A-adrenoceptors or histamine H1 and muscarinic M3 receptors. Thus, the antagonism by NF449 is highly specific for P2 receptors. In conclusion, the subnanomolar potency at rP2X1 receptors and the rank order of potency, P2X1 >> P2X3 > P2Y1 > P2Y2 > ecto-nucleotidases, make NF449 unique among the P2 receptor antagonists reported to date. NF449 may fill the long-standing need for a P2X1-selective radioligand.

Animals↗
PubMed2000

The suramin analogue NF279 is a novel and potent antagonist selective for the P2X(1) receptor.

The suramin analogue 8,8'-(carbonylbis(imino-4, 1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)) bis(1,3,5-naphthalenetrisul fonic acid) (NF279) was analysed with respect to its potency and P2X receptor subtype selectivity. Two-electrode voltage-clamp measurements were performed with Xenopus laevis oocytes expressing homomultimeric rat P2X(1), P2X(2), P2X(3) and human P2X(4) receptors. For the fast desensitising P2X(1) and P2X(3) receptors, IC(50) values strongly depended on whether oocytes were pre-incubated with NF279 prior to ATP superfusion or exposed to NF279 simultaneously with ATP. With a 10 s pre-incubation period of NF279, IC(50) values of 19 nM and 1.62 microM were obtained for rat P2X(1) and P2X(3), respectively. Without pre-incubation, IC(50) values amounted to 2 microM and 85.5 microM for P2X(1) and P2X(3), respectively. For the non-desensitising rat P2X(2) receptor NF279 appeared to act as a competitive antagonist with an IC(50) value of 0.76 microM and a K(B) value of 0.36 microM, as derived from Schild analysis. P2X(4) receptors were the least sensitive subtypes for NF279 (IC(50)>300 microM). The antagonism was fully reversible at all P2X subtypes analysed. Our results indicate that NF279 is a potent P2X(1) receptor-selective and reversible antagonist.

Adenosine Triphosphate↗
PubMed2000

The novel heteromeric bivalent ligand SB9 potently antagonizes P2Y(1) receptor-mediated responses.

Effects of 6-[(4,6,8-trisulfo-1-naphthyl)iminocarbonyl-1, 3-(4-methylphenylene)iminocarbonyl-1, 3-phenylene-azo]-pyridoxal-5'-phosphate (SB9), a heterodimeric bivalent ligand consisting of pyridoxal-5'-phosphate and the suramin monomer, were studied on contractions of the rat vas deferens elicited by alpha beta-methylene ATP (alpha beta meATP; mediated by P2X(1)-like receptors), contractions of the guinea-pig ileal longitudinal smooth muscle elicited by adenosine 5'-O-(2-thiodiphosphate) (ADP beta S mediated by P2Y(1)-like receptors), and the degradation of ATP by ecto-nucleotidases in folliculated Xenopus laevis oocytes. SB9 (0.1-10 microM) antagonized contractile responses produced by alpha beta meATP or ADP beta S in a concentration-dependent manner. Schild analysis yielded linear regression lines of unit slope, indicating competitive antagonism. From the rightward shifts of the agonist concentration-response curves pA(2) values of 6.05+/-0.13 (vas deferens) and 6.98+/-0.07 (ileum) were derived. In both preparations, SB9 behaved as a slow onset, slow offset antagonist. Incubation of three oocytes in the presence of ATP produced an increase in inorganic phosphate (P(i)) over a 30-min period, which amounted to 35.1+/-1.9 microM P(i) from 100 microM ATP. SB9 (10-1000 microM) reduced this degradation (pIC(50)=4.33+/-0.10). The results illustrate that SB9 is a high-affinity P2Y(1) receptor antagonist with a remarkable selectivity for P2Y(1) vs. P2X(1) receptors (about 10-fold) and ecto-nucleotidases (447-fold). These properties make it unique among the pyridoxal-5'-phosphate and suramin derivatives reported to date.

5'-Nucleotidase↗
PubMed2000

Antagonism by the suramin analogue NF279 on human P2X(1) and P2X(7) receptors.

The effect of the suramin analogue 8,8'-(carbonylbis(imino-4, 1-phenylenecarbonylimino-4,1-phenylenecarbonylimino))bis(1,3 , 5-naphthalenetrisulfonic acid) (NF279) was analyzed on human P2X(1) and P2X(7) receptor subtypes (human P2X(1) and human P2X(7)) heterologously expressed in Xenopus oocytes using the two-microelectrode voltage-clamp technique. At activating ATP concentrations of 1 microM (human P2X(1)) and 10 microM ATP (human P2X(7)), IC(50) values of 0.05 microM and 2.8 microM were found for human P2X(1) and human P2X(7) receptors, respectively. An increase in the activating [ATP] shifted the NF279 concentration-inhibition curve rightwards for both receptors. NF279 slowed the activation of both human P2X(1) and human P2X(7) as well as the desensitization of human P2X(1). The data support a model in which desensitization of P2X(1) is dependent on preceding activation of these P2X receptors. It is concluded that NF279 acts as a competitive antagonist with much higher potency at human P2X(1) than at P2X(7) receptors. NF279 may hence be suited to discriminate between both receptors in native tissues.

Animals↗
PubMed2000

The novel pyridoxal-5'-phosphate derivative PPNDS potently antagonizes activation of P2X(1) receptors.

Pyridoxal-5'-phosphate-6-(2'-naphthylazo-6'-nitro-4',8'-disulfonat e) (PPNDS) potently antagonized P2X(1) receptor-mediated responses in rat vas deferens (pK(B)=7.43) and Xenopus laevis oocytes (pIC(50)=7. 84). It showed lower (up to 20,000-fold) inhibitory potency on ecto-nucleotidase in Xenopus oocytes and on P2Y(1) receptors in guinea-pig ileum (pA(2)=6.13). PPNDS did not interact with alpha(1A)-adrenoceptors, adenosine A(1) and A(2B), histamine H(1) and muscarinic M(3) receptors. Thus, PPNDS is a novel, specific P2 receptor antagonist and represents the pyridoxal-5'-phosphate derivative with the highest potency at P2X(1) receptors.

Animals↗
PubMed2000

Agonists and antagonists acting at P2X receptors: selectivity profiles and functional implications.

P2X receptors are nucleotide-gated cation channels composed of homomeric or heteromeric assemblies of three subunits. In the past 7 years, an extended series (P2X1-7) of P2X subunits has been cloned from vertebrate tissues. In this rapidly expanding field, one of the main current challenges is to relate the cloned P2X receptor subtypes to the diverse physiological responses mediated by the native P2X receptors. However, the paucity of useful ligands, especially subtype-selective agonists and antagonists as well as radioligands, acts as a considerable impediment to progress. Most of the ligands available are highly limited in terms of their kinetics of action, receptor-affinity, subtype-selectivity and P2X receptor-specificity. Their suspected ability to be a substrate for ecto-nucleotidases or to inhibit these enzymes also complicates their use. A number of new antagonists at P2X receptors have recently been described which to some degree are more potent and more selective than earlier antagonists like suramin or pyridoxal-5'-phosphate-6-azophenyl 2',4'-disulfonate (PPADS). This work moves us closer to the ideal goal of classifying the recombinant and native P2X receptor subtypes on the basis of antagonist profiles. This review begins with a brief account of the current status of P2X receptors. It then focuses on the pharmacological properties of a series of key P2 receptor agonists and antagonists and will finish with the discussion of some related therapeutic possibilities.

Animals↗
PubMed2000

Functional role of muscarinic M(2) receptors in alpha,beta-methylene ATP induced, neurogenic contractions in guinea-pig ileum.

1. The muscarinic acetylcholine receptors mediating the contractile response elicited to endogenous acetylcholine released by the selective P2X receptor agonist alpha,beta-methylene ATP (mATP) were investigated in guinea-pig ileum. 2. mATP (0.1 - 30 microM) elicited a concentration-dependent neurogenic contractile response inhibited by tetrodotoxin (TTX) and antagonized by the non-selective muscarinic receptor antagonist N-methylscopolamine (NMS). 3. The contractile response to mATP was pertussis toxin-insensitive, irreversibly antagonized by N-(2-chloroethyl)-4-piperidinyl diphenylacetate (4-DAMP mustard), and unaffected by the muscarinic M(2)/M(4) receptor selective antagonist AF-DX 116 (1 microM). 4. When measured in the presence of histamine and isoproterenol after treatment with 4-DAMP mustard, mATP elicited a pertussis toxin-sensitive contractile response potently antagonized by AF-DX 116. 5. Collectively, our data suggest that endogenous acetylcholine released by mATP can elicit a direct contractile response through the muscarinic M(3) receptor and an indirect contractile response through the muscarinic M(2) receptor by antagonizing the relaxant effects of isoproterenol on histamine induced contraction.

Adenosine Triphosphate↗
PubMed2000

Muscarinic properties of compounds related to arecaidine propargyl ester.

A series of new analogues of the arecaidine propargyl ester (CAS 35516-99-5), APE, 1a) with alcohols consisting of 4 or 5 carbon atoms were investigated at muscarinic receptor subtypes. The muscarinic activity of the quaternary and tertiary salts of the APE-related compounds were assayed on the isolated guinea-pig ileum (M3 receptor subtype) and guinea-pig left atria (M2 receptor subtype) as well as on rabbit isolated vas deferens (M1 receptor subtype). The structural variations made in the APE molecule, replacing the triple bond in the ester side chain with structures such as double bond, an allene moiety, a single bond, a cyclopropyl group or two triple bonds should alter the selectivity and potency in favour of the M2 subtype. Enhanced, though modest, selectivity for M2 receptors was achieved with the 2-butynyl ester 2a. The other structural variations resulted in a loss of potency, but not necessarily of efficacy.

Animals↗
PubMed1999

Neuronal soma-dendritic and prejunctional M1-M4 receptors in gastrointestinal and genitourinary smooth muscle.

A variety of neurons in gastrointestinal and genitourinary smooth muscle express muscarinic auto- as well as heteroreceptors. These receptors are found on the soma and dendrites of many cholinergic, sympathetic and NANC neurons and on axon terminals. A given neuron may contain both excitatory and inhibitory presynaptic muscarinic receptors. The subtypes involved are species- and tissue-dependent, and neuronal M1 to M4 receptors have been shown to be expressed in smooth muscle tissues. In this study, the ability of several selective muscarinic receptor antagonists to inhibit the effect of arecaidine propargyl ester (APE) on prejunctional muscarinic receptors on sympathetic nerve endings in the rabbit anococcygeus muscle (RAM) was investigated to characterise the receptor subtype involved. Electrical field stimulation (EFS) resulted in a release of noradrenaline (NA) eliciting monophasic contractions due to stimulation of postjunctional alpha1-adrenoceptors. The selective muscarinic agonist APE did not reduce contractions to exogenous NA, but caused a concentration-related and N-methylatropine-sensitive inhibition of neurogenic responses. All muscarinic antagonists investigated failed to affect the EFS-induced contractions, but shifted the concentration-response curve of APE to the right in a parallel and surmountable fashion. Schild analysis yielded regression lines of unit slope, indicating competitive antagonism. The following rank order of antagonist potencies (pA2 values) was found: tripitramine (9.10) > AQ-RA 741 (8.26) > or = himbacine (8.04) > or = (S)-dimethindene (7.69) > pirenzepine (6.46) > or = p-F-HHSiD (6.27). A comparison of the pA2 values determined in the present study with literature binding and functional affinities obtained at native or recombinant M1 to M5 receptors strongly suggests that NA release from sympathetic nerve endings in RAM is inhibited by activation of prejunctional muscarinic M2 receptors.

Adrenergic alpha-Antagonists↗
PubMed1999

Antagonistic properties of the suramin analogue NF023 at heterologously expressed P2X receptors.

The suramin analogue 8,8'-(carbonylbis(imino-3,1-phenylene carbonylimino)bis(1,3,5-naphthalenetrisulfonic acid) (NF023) antagonizes in a competitive fashion P2X receptor-mediated responses in certain vascular and visceral smooth muscles. In the present study, the effect of NF023 on voltage-clamped Xenopus oocytes heterologously expressing homomultimeric P2X1-P2X4 as well as heteromultimeric P2X2/P2X3 receptors has been characterized. P2X1 receptors were most sensitive to inhibition by NF023 with IC50 values of 0.24 and 0.21 microM for the rat and human homologue, respectively. P2X3 receptors have an intermediate sensitivity with IC50 values of 8.5 and 28.9 microM for rat and human subtypes, respectively and P2X2 was the least sensitive subtype (IC50 > 50 microM). P2X4 receptors were insensitive to NF023 at concentrations up to 100 microM. Coexpression of rat P2X3 with rat P2X2 resulted in receptors whose sensitivity to NF023 was identical to that obtained for homomultimeric rat P2X3 receptors (alphabeta meATP as agonist; IC50 = 1.4 and 1.6 microM, respectively). NF023 inhibited P2X1 receptors in a voltage-insensitive manner. In addition, NF023 (5 and 30 microM) caused a shift of the concentration-response curve to the right without affecting the maximal response to ATP (K(B) = 1.1 +/- 0.2 microM). Our results indicate that NF023 is a subtype-selective and surmountable antagonist at P2X1 receptors heterologously expressed in Xenopus oocytes.

Adenosine Triphosphate↗
PubMed1999

Novel ligands for P2 receptor subtypes in innervated tissues.

Among suramin analogues, the properties of P2 receptor subtype blockade and ecto-nucleotidase inhibition appear to be controlled by different structural parameters (Fig. 1 and 2, Table 1; Van Rhee et al., 1994; Beukers et al., 1995; Bültmann et al., 1996; Damer et al., 1998a, 1998b; and this study): the molecular size of the compounds, the position of the sulfonic acid residues in the naphthalene rings, the substitution pattern of the benzoyl moieties and the 3'- or 4'-aminobenzoyl-linkages of the phenyl rings "1" and "2". As a result, compounds with different receptor selectivity profiles were obtained. A maximum in potency at and selectivity for P2X1 receptors is reached in NF279, which is a specific P2 receptor antagonist and the compound with the highest P2X1 vs. P2Y receptor and ecto-nucleotidase selectivity presently available.

Adenosine Triphosphate↗
PubMed1998

P2X1 and P2X3 receptors form stable trimers: a novel structural motif of ligand-gated ion channels.

UNLABELLED: P2X receptors are cation channels gated by extracellular ATP. The seven known P2X isoforms possess no sequence homology with other proteins. Here we studied the quaternary structure of P2X receptors by chemical cross-linking and blue native PAGE. P2X1 and P2X3 were N-terminally tagged with six histidine residues to allow for non-denaturing receptor isolation from cRNA-injected, [35S]methionine-labeled oocytes. The His-tag did not change the electrophysiological properties of the P2X1 receptor. His-P2X1 was found to carry four N-glycans per polypeptide chain, only one of which acquired Endo H resistance en route to the plasma membrane. 3, 3'-Dithiobis(sulfosuccinimidylpropionate) (DTSSP) and two of three bifunctional analogues of the P2X receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) cross-linked digitonin-solubilized His-P2X1 and His-P2X3 quantitatively to homo-trimers. Likewise, when analyzed by blue native PAGE, P2X receptors purified in digitonin or dodecyl-beta-D-maltoside migrated entirely as non-covalently linked homo-trimers, whereas the alpha2 beta gamma delta nicotinic acetylcholine receptor (used as a positive control) migrated as the expected pentamer. P2X monomers remained undetected soon after synthesis, indicating that trimerization occurred in the endoplasmic reticulum. The plasma membrane form of His-P2X1 was also identified as a homo-trimer. If n-octylglucoside was used for P2X receptor solubilization, homo-hexamers were observed, suggesting that trimers can aggregate to form larger complexes. We conclude that trimers represent an essential element of P2X receptor structure. KEYWORDS: blue native PAGE/cross-linking/P2X receptor/quaternary structure.

Animals↗
PubMed1998

NF279: a novel potent and selective antagonist of P2X receptor-mediated responses.

8,8'-(Carbonylbis(imino-4, 1 -phenylenecarbonylimino-4,1-phenylenecarbonylimino))bis(1,3, 5-naphthalenetrisulfonic acid) (NF279) antagonized P2X receptor-mediated contractions in rat vas deferens, evoked by alpha,beta-methylene ATP (10 microM; pIC50=5.71) without affecting responses mediated via alpha1A-adrenoceptors, adenosine A1 and A2B receptors, histamine H1, muscarinic M3 and nicotinic receptors. The low inhibitory potency of NF279 on P2Y receptors in guinea-pig taenia coli (pA2=4.10) and at ecto-nucleotidases in folliculated Xenopus laevis oocytes (IC50 > 100 microM) indicates that NF279 is a novel specific and selective P2X receptor antagonist.

Adenosine Triphosphate↗
PubMed1998

M2 receptor binding of the selective antagonist AF-DX 384: possible involvement of the common allosteric site.

The hypothesis was tested that M2-selective antagonists partially utilize the allosteric site of muscarinic M2 receptors. The interactions of the allosteric agent W84 (hexane-1, 6-bis[dimethyl-3'-phthalimidopropyl-ammonium bromide]) were studied with the M2/M4-selective AF-DX 384 [(+/-)-5, 11-dihydro-11-([(2-(2-[(dipropylamino)methyl]-1-piperidinyl)ethyl)amino]carbonyl)-6H-pyrido(2,3-b)(1,4)-benzodiazepine-6-one], the nonselective N-methylscopolamine (NMS), and a number of other muscarinic antagonists. In isolated paced guinea pig atria, the antagonistic effect of W84 against oxotremorine- and arecaidine propargyl ester-induced negative inotropic actions reached a limiting value at higher W84 concentrations, revealing negative cooperativity (factors of cooperativity alpha = 311 and alpha = 495, respectively). The antagonistic potency of W84 in this M2 receptor model (W84 binding constant KA approximately 160 nM) was higher than at M1/M4-like receptors of rabbit vas deferens (KB approximately 800 nM) and at M3 receptors of guinea pig ileum (KB approximately 4,000 nM). In paced atria, combinations of W84 with muscarinic antagonists yielded more-than-additive antagonistic effects against oxotremorine in case of conventional antagonists such as NMS (alpha = 18) but less-than-additive effects with the M2-preferring AF-DX 384 (alpha = 444). In guinea pig heart homogenates, the equilibrium binding of [3H]NMS was only partially inhibited by W84 (alpha = 2.4), whereas [3H]AF-DX 384 binding could be suppressed completely (alpha = 194). The difference in cooperativity reflects that W84 inhibits [3H]NMS dissociation with a approximately 40-fold higher potency (ECdiss = 900 nM) than [3H]AF-DX 384 dissociation (ECdiss = 33,300 nM). [3H]NMS dissociation also could be retarded by AF-DX 384 (ECdiss = 22,000 nM), probably via an interaction with the site used by W84. The results suggest that the binding domain of AF-DX 384 partially overlaps with the common allosteric site of the M2 receptor protein.

Allosteric Regulation↗
PubMed1997

Quantitative colorimetric and gas chromatographic determination of arecaidine propargyl ester.

Arecaidine propargyl ester (APE) is a potent muscarinic agonist often used in pharmacological studies. To date, no sensitive quantitative analytical method for APE has been published. In this study, two methods for the quantitative determination of APE are compared: a colorimetric assay, based on the formation of the corresponding ferric(III)-hydroxamic acid complex, and a direct gas chromatographic method, using arecoline as the internal standard. The latter method was found to be more precise. The utility of the gas chromatographic assay was further demonstrated in a stability study of the drug in the biological fluid aqueous humor of rabbits.

Animals↗