Influence of Tissue Integrity on Pharmacological Phenotypes of Muscarinic Acetylcholine Receptors in the Rat Cerebral Cortex

Anisuzzaman, Abu Syed Md; Nishimune, Atsushi; Yoshiki, Hatsumi; Uwada, Junsuke; Muramatsu, Ikunobu

doi:10.1124/jpet.111.182857

Cited by 11 publications

(16 citation statements)

References 33 publications

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“…In addition to this possibility, the present study confirms that the multiple binding sites are also influenced by receptor environment (tissue integrity and tissue/cell background), resulting in distinct phenotypes/states (Baker and Hill, ; Nelson and Challiss, ; Nishimune et al ., ). Like the present α 1B ‐adrenoceptor, atypical properties have been found to date in several receptors and tissues under intact cell/tissue conditions: histamine H 2 ‐receptor in guinea pig hippocampus (Tuong et al ., ), β 3 ‐adrenoceptor in CHO cells (Arch, ), M 3 ‐muscarinic ACh receptors in rat cerebral cortex (Anisuzzaman et al ., ) and α 1L ‐adrenoceptors in lower urinary tract of humans and rodents and in rat cerebral cortex (Morishima et al ., 2007; 2008; Muramatsu et al ., ), all of which converted into traditional/representative receptor phenotype showing high affinity for selective antagonists of each receptor in cell‐free preparations.…”

Section: Discussionmentioning

confidence: 99%

Pharmacologically distinct phenotypes of α_1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Yoshiki

Uwada

Anisuzzaman

et al. 2014

British J Pharmacology

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BACKGROUND AND PURPOSEThe pharmacological properties of particular receptors have recently been suggested to vary under different conditions. We compared the pharmacological properties of the α1B-adrenoceptor subtype in various tissue preparations and under various conditions. EXPERIMENTAL APPROACH[ 3 H]-prazosin binding to α1B-adrenoceptors in rat liver (segments, dispersed hepatocytes and homogenates) was assessed and the pharmacological profiles were compared with the functional and binding profiles in rat carotid artery and recombinant α1B-adrenoceptors. KEY RESULTSIn association and saturation-binding experiments with rat liver, binding affinity for [ 3 H]-prazosin varied significantly between preparations (KD value approximately ten times higher in segments than in homogenates). The binding profile for various drugs in liver segments also deviated from the representative α1B-adrenoceptor profile observed in liver homogenates and recombinant receptors. L-765,314 and ALS-77, selective antagonists of α1B-adrenoceptors, showed high binding and antagonist affinities in liver homogenates and recombinant α1B-adrenoceptors. However, binding affinities for both ligands in the segments of rat liver and carotid artery were 10 times lower, and the antagonist potencies in α1B-adrenoceptor-mediated contractions of carotid artery were more than 100 times lower than the representative α1B-adrenoceptor profile. CONCLUSIONS AND IMPLICATIONSIn contrast to the consistent profile of recombinant α1B-adrenoceptors, the pharmacological profile of native α1B-adrenoceptors of rat liver and carotid artery varied markedly under various receptor environments, showing significantly different binding properties between intact tissues and homogenates, and dissociation between functional and binding affinities. In addition to conventional 'subtype' characterization, 'phenotype' pharmacology must be considered in native receptor evaluations in vivo and in future pharmacotherapy.

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Section: Discussionmentioning

confidence: 99%

Pharmacologically distinct phenotypes of α_1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Yoshiki

Uwada

Anisuzzaman

et al. 2014

British J Pharmacology

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“…Binding data were analysed using PRISM (Version 5.01, Graph Pad Software, La Jolla, CA, USA), as previously described (Anisuzzaman et al., 2011). Briefly, the data from saturation binding studies were fitted by a one‐site saturation binding isotherm (Binding‐Saturation Equation in PRISM), and the K D values and the binding capacity were then calculated.…”

Section: Methodsmentioning

confidence: 99%

Regional quantification of muscarinic acetylcholine receptors and β‐adrenoceptors in human airways

Ikeda

Anisuzzaman

Yoshiki

et al. 2012

British J Pharmacology

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BACKGROUND AND PURPOSEMuscarinic acetylcholine receptors (mAChRs) and b-adrenoceptors in the airways and lungs are clinically important in chronic obstructive pulmonary disease (COPD) and asthma. However, the quantitative and qualitative estimation of these receptors by radioligand binding approaches in human airways has not yet been reported because of tissue limitations. EXPERIMENTAL APPROACHThe regional distribution and relative proportion of mAChR and b-adrenoceptor subtypes were evaluated in human bronchus and lung parenchyma by a tissue segment binding method with [ KEY RESULTSThe M3 subtype predominantly occurred in the bronchus, but the density decreased from the segmental to subsegmental bronchus, and was absent in lung parenchyma. On the other hand, the M1 subtype occurred in the lung only, and the M2 subtype was distributed ubiquitously in the bronchus and lungs. b2-adrenoceptors were increased along the airways, and their densities in the subsegmental bronchus and lung parenchyma were approximately twofold higher than those of mAChRs in the same region. b1-adrenoceptors were also detected in lung parenchyma but not in the bronchus. The muscarinic contractions and adrenoceptor relaxations in both bronchial regions were mediated through M3-mAChRs and b2-adrenoceptors, respectively. CONCLUSIONS AND IMPLICATIONSFrom the present radioligand binding approach with intact tissue segments, we constructed a distribution map of mAChRs and b-adrenoceptors in human bronchus and lung parenchyma for the first time, providing important evidence for future pharmacotherapy and new drug development for respiratory disorders.

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“…Likewise, doxepine (K d of 1.4 μM in dissociated tissue and 0.17 μM for homogenates) and amitriptyline (K d of 1.9 μM in dissociated tissue, 3.5 μM in slices, and 0.034 μM for homogenates) showed very heterogeneous results (Kanba and Richelson 1983). Such striking impact on tissue integrity on ligand affinities is not limited to the H 2 R, but has been recently observed for muscarinic acetylcholine receptors (Anisuzzaman et al 2011). Thus, the discrepancies in ligand affinities between intact tissue and membrane preparations appear to be of more general pharmacological importance.…”

Section: Structure-activity Relationships For Antidepressants and Antmentioning

confidence: 78%

Interactions of recombinant human histamine H1, H2, H3, and H4 receptors with 34 antidepressants and antipsychotics

Appl

Holzammer

Dove

et al. 2011

Naunyn-Schmiedeberg's Arch Pharmacol

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Antidepressants and antipsychotics affect multiple molecular targets. Consequently, these drugs exhibit not only unique profiles of therapeutic effects but also several undesired effects. Histamine receptors (H₁R, H₂R, H₃R, and H₄R) belong to the large family of G protein-coupled receptors and are very important drug targets. All four H(x)R subtypes are expressed in the CNS. Interactions of lipophilic, blood-brain barrier-penetrating drugs with H(x)Rs could contribute to therapeutic and unwanted effects. Therefore, we investigated potencies H(x)R as well as potencies and (inverse) agonistic efficacies of 34 antidepressants and antipsychotics at HxRs in functional assays. We expressed human H(x)Rs in Sf9 insect cells and conducted radioligand competition binding experiments and functional steady-state GTPase assays. Ligand affinities and potencies were compared with literature data and related to therapeutic reference ranges. Almost all antidepressants and antipsychotics displayed high binding affinities to H₁R and behaved as antagonists. The atypical antidepressant trimipramine behaved as a high-affinity/high-potency H₂R antagonist (pK(i), 7.39; pK(B), 7.36; pA₂, 7.55). Docking to an H₂R model suggested a probable binding mode. The affinity of antidepressants and antipsychotics for H₃R was low. The atypical antipsychotic clozapine, known to induce agranulocytosis, exhibited partial H₄R agonism for which docking experiments provided a molecular basis. Clozapine also exhibited H₂R antagonism. We observed dissociations between pK(i) and pK (B) values as well as between pK(i) and pIC₅₀ values for H(x)Rs. Antidepressants and antipsychotics interact differentially with H(x)Rs. The concept of functional selectivity (also referred to as ligand-specific receptor conformations or biased signaling) explains dissociations between pK(i) and pK(B) values as well as differences between pK(i) and pIC₅₀ values. The H₁R antagonism of numerous antidepressants and antipsychotics is very pronounced. The H₂R antagonism of trimipramine and partial H₄R agonism of clozapine may be clinically relevant. We also discuss the possible role of the H₂R antagonism of clozapine for neutropenia/agranulocytosis induced by this compound. Finally, we discuss the methodological, conceptual, and clinical limitations of our study.

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Influence of Tissue Integrity on Pharmacological Phenotypes of Muscarinic Acetylcholine Receptors in the Rat Cerebral Cortex

Abstract: Distinct pharmacological phenotypes of muscarinic acetylcholine receptors (mAChRs) have been proposed. We compared the pharmacological profiles of mAChRs in intact segments and homogenates of rat cerebral cortex and other tissues by using radioligand binding assays with

Cited by 11 publications

References 33 publications

Pharmacologically distinct phenotypes of α_1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Pharmacologically distinct phenotypes of α_1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Regional quantification of muscarinic acetylcholine receptors and β‐adrenoceptors in human airways

Interactions of recombinant human histamine H1, H2, H3, and H4 receptors with 34 antidepressants and antipsychotics

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Influence of Tissue Integrity on Pharmacological Phenotypes of Muscarinic Acetylcholine Receptors in the Rat Cerebral Cortex

Abstract: Distinct pharmacological phenotypes of muscarinic acetylcholine receptors (mAChRs) have been proposed. We compared the pharmacological profiles of mAChRs in intact segments and homogenates of rat cerebral cortex and other tissues by using radioligand binding assays with

Cited by 11 publications

References 33 publications

Pharmacologically distinct phenotypes of α1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Pharmacologically distinct phenotypes of α1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Regional quantification of muscarinic acetylcholine receptors and β‐adrenoceptors in human airways

Interactions of recombinant human histamine H1, H2, H3, and H4 receptors with 34 antidepressants and antipsychotics

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Pharmacologically distinct phenotypes of α_1B‐adrenoceptors: variation in binding and functional affinities for antagonists

Pharmacologically distinct phenotypes of α_1B‐adrenoceptors: variation in binding and functional affinities for antagonists