### A. Overview

Extracellular purines (adenosine, ADP, and ATP) and pyrimidines (UDP and UTP) are important signaling molecules that mediate diverse biological effects via cell-surface receptors termed purine receptors. In this review particular emphasis is placed on the discrepancy between the

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Receptors for Purines and Pyrimidines

Background Controlled clinical trials have shown that beta-blockers can produce hemodynamic and symptomatic improvement in chronic heart failure, but the effect of these drugs on survival has not been determined. Methods We enrolled 1094 patients with chronic heart failure in a double-blind, placebo-controlled, stratified program, in which patients were assigned to one of four treatment protocols on the basis of their exercise capacity. Within each of the four protocols patients with mild, moderate, or severe heart failure with left ventricular ejection fractions ≤0.35 were randomly assigned to receive either placebo (n = 398) or the beta-blocker carvedilol (n = 696); background therapy with digoxin, diuretics, and an angiotensin-converting–enzyme inhibitor remained constant. Patients were observed for the occurrence of death or hospitalization for cardiovascular reasons during the following 6 months (12 months for the group with mild heart failure). Results The overall mortality rate was 7.8 percent in t...

The Effect of Carvedilol on Morbidity and Mortality in Patients With Chronic Heart Failure

▪ Abstract In the mid to late 1980s, studies were published that provided the first evidence for the existence of glutamate receptors that are not ligand-gated cation channels but are coupled to effector systems through GTP-binding proteins. Since those initial reports, tremendous progress has been made in characterizing these metabotropic glutamate receptors (mGluRs), including cloning and characterization of cDNA that encodes a family of eight mGluR subtypes, several of which have multiple splice variants. Also, tremendous progress has been made in developing new highly selective mGluR agonists and antagonists and toward determining the physiologic roles of the mGluRs in mammalian brain. These findings have exciting implications for drug development and suggest that the mGluRs provide a novel target for development of therepeutic agents that could have a significant impact on neuropharmacology.

Pharmacology and functions of metabotropic glutamate receptors.

Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Physiology of Microglia

P2X receptors are membrane ion channels that open in response to the binding of extracellular ATP. Seven genes in vertebrates encode P2X receptor subunits, which are 40–50% identical in amino acid ...

Molecular Physiology of P2X Receptors

A variety of muscarinic antagonists are currently used as tools to pharmacologically subclassify muscarinic receptors into M1, M2 and M3 subtypes. In the present study, we have determined the affinity profiles of several of these antagonists at five cloned human muscarinic receptors (m1-m5) stably expressed in Chinese hamster ovary cells (CHO-K1). At all five receptors, the (R)-enantiomers of trihexyphenidyl and hexbutinol displayed considerably higher affinities (up to 525-fold) than their corresponding (S)-isomers. The stereoselectivity ratios [inhibition constant(S)/inhibition constant(R)] for both pairs of enantiomers were lowest at m2 receptors, suggesting that less stringent configurational demands are made by this receptor subtype. The "M1-selective" antagonist (R)-trihexyphenidyl displayed high affinities for m1 and m4 receptors. The "M2-selective" antagonists himbacine, (+-)-5,11-dihydro-11- ([(2-[(dipropylamino)methyl]-1- piperidinyl)ethyl)amino]carbonyl)-6H-pyrido(2,3-b)(1,4)benzodiazepine-6- one (AF-DX 384), 11-[4-[4-(diethylamino)butyl]-1-piperidinyl)acetyl)-5,11- dihydro-6H-pyrido(2,3-b) (1,4)benzodiazepine-6-one (AQ-RA 741) and (+)-(11-[2-[(diethylamino) methyl]-1-piperidinyl)acetyl)-5,11-di-hydro-6H-pyrido(2,3-b)(1,4) benzodiazepine-6-one [AF-DX 250; the (+)-enantiomer of AF-DX 116] exhibited high affinities for m2 and m4, intermediate affinities for m1 and m3 and low affinities for m5 receptors. This selectivity profile was most prominent for AQ-RA 741, which displayed 195- and 129-fold higher affinities for m2 and m4 receptors than for m5 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

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Antagonist binding profiles of five cloned human muscarinic receptor subtypes.

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

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

PPADS, a novel functionally selective antagonist of P2 purinoceptor-mediated responses.

1.

The contractile effect of 5-HT in the isolated longitudinal ileal muscle of adult guinea-pigs was studied over a large concentration range.




2.

5-HT produced a biphasic concentration-response curve indicative of an interaction with at least two indenpendent populations of receptors. The concentrations which elicited half-maximal effects for the first and the second phases of the concentration-response curve were estimated as 1.5±1.2×10−8 mol/l and 1.3±0.4×10−6 mol/l respectively. The maximal response produced by the interaction of 5-HT with the high affinity receptor (i. e. first phase) was calculated as 27±9.3% of the total response.




3.

The biphasic concentration-response was not influenced by methysergide (10−6 mol/l).




4.

The effect of low concentrations of 5-HT (<3×10−7 mol/l) was antagonised by atropine (10−7 mol/l), tetrodotoxin (TTX) (10−6 mol/l), morphine (10−5 mol/l), the substance P antagonist,d-Pro4,d-Trp7,9-SP4–11 (3×10−5 mol/l) and capsaicin (10−5 mol/l). Physostigmine (10−7 mol/l) augmented the effect.




5.

The response to high concentrations of 5-HT (3×10−7–3×10−6 mol/l) was antagonised by ICS 205-930 andd-Pro4,d-Trp7,9-SP4–11 in a competitive manner and was inhibited by TTX, morphine and capsaicin in an insurmountable way.




6.

The effect of very high concentrations of 5-HT (>10−5 mol/l) could be partially antagonised by methysergide (10−7 mol/l) in the presence of ICS 205-930 (10−7 mol/l) and totally by a combination of methysergide and TTX.




7.

We conclude that in longitudinal muscle strips from the ileum of adult guinea-pigs a contractile action of 5-HT can be mediated by the activation of three independent receptors. At concentrations below 3×10−7 mol/l 5-HT causes the release of substance P which subsequently releases acetylcholine. At concentrations higher than 3×10−7 mol/l 5-HT releases substance P which then directly activates SP-receptors on the smooth muscle cells. The stimulation of postjunctional 5-HT D-receptors only occurs at concentrations of 5-HT greater than 10−5 mol/l, and thus appears to be of minor importance.

Study of the contractile effect of 5-hydroxytryptamine (5-HT) in the isolated longitudinal muscle strip from guinea-pig ileum. Evidence for two distinct release mechanisms.

Ernst Mutschler

Papers

Antagonist binding profiles of five cloned human muscarinic receptor subtypes.

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

PPADS, a novel functionally selective antagonist of P2 purinoceptor-mediated responses.

Study of the contractile effect of 5-hydroxytryptamine (5-HT) in the isolated longitudinal muscle strip from guinea-pig ileum. Evidence for two distinct release mechanisms.

Predictability of the covalent binding of acidic drugs in man