Interaction of Psychotropic Drugs with Brain Muscarinic Cholinoceptors: Similarities of Biperiden with Pirenzepine in Receptor Binding Properties (original) (raw)
Related papers
Antagonism by antidepressants of muscarinic acetylcholine receptors of human brain
British Journal of Pharmacology, 1983
Twenty-two compounds classified as antidepressants, metabolites of antidepressants or putative antidepressants were assayed for their ability to antagonize the binding of (-)-[3H]-quinuclidinyl benzilate to muscarinic receptors in homogenates of human caudate nucleus. 2 Sixteen of these compounds were assayed for their ability to antagonize carbachol-stimulated cyclic guanosine 3',5'-monophosphate (cyclic GMP) synthesis by intact murine neuroblastoma cells (clone NlE-115). 3 Equilibrium dissociation constants (KDS) for these drugs and the muscarinic receptors of human brain spanned over 4 orders of magnitude, with the tertiary amine tricyclic antidepressant, amitriptyline (KD = 18 nM) being the most potent compound tested and trazodone (KD = 324 tMM) the least potent. 4 There was a significant correlation between the data for human and murine receptors and for eight compounds (imipramine, desipramine, maprotiline, mianserin, 3-chloro-2hydroxyimipramine, amoxapine, 2-hydroxyimipramine and iprindole). KD values measured by the two techniques were not significantly different.
Inverse agonist activity of pirenzepine at M 2 muscarinic acetylcholine receptors
British Journal of Pharmacology, 1999
1. The intrinsic properties of muscarinic ligands were studied through their binding properties and their abilities to modulate the GTPase activity of G proteins coupled to muscarinic M2 receptors in pig atrial sarcolemma. 2. Competition binding experiments were performed with [3H]-oxotremorine-M to assess the affinity of receptors coupled to G proteins (R*), with [3H]-N-methylscopolamine ([3H]-NMS) to estimate the affinities of coupled and uncoupled receptors (R*+R) and with [3H]-NMS in the presence of GppNHp to assess the affinity of uncoupled receptors (R). 3. The ranking of Ki values for the agonist carbachol was R*<R*+R<R (0.95, 124 and 1017 nM). Ki values for atropine and AF-DX 116 were similar for the three binding conditions (0.34, 0.42, 0.41 and 19, 22, 32 nM). The ranking of Ki values for pirenzepine was R*>R*+R>R (174, 155, 115 nM), suggesting inverse agonism. 4. The Vmax of the basal high affinity GTPase activity of pig atrial sarcolemma was increased by mastoparan and decreased by GPAnt-2 indicating the relevance of this activity to G proteins coupled to receptors (R*). The K(M) value (0.26-0.33 microM) was not modified by mastoparan or GPAnt-2. 5. Carbachol increased the Vmax of GTP hydrolysis (EC50 8.1+/-0.3 microM), whereas atropine and AF-DX 116, up to 1 mM, did not modify it. Pirenzepine decreased the Vmax of GTP hydrolysis (EC50 77.5+/-10.3 microM). This effect was enhanced when KCI was substituted for NaCl (EC50 11.0+/-0.8 microM) and was antagonized by atropine and AF-DX 116 (IC50 0.91+/-0.71 and 197+/-85 nM). 6. Pirenzepine is proposed as an inverse agonist and atropine and AF-DX 116 as neutral antagonists at the muscarinic M2 receptor.
Journal of Neural Transmission, 1988
The muscarinic acetylcholine receptor was solubilized from rat brain cortex by the zwitter-ionic detergent, 3-((3-cholamidopropyl)dimethylamino)-1-propane sulfonate (CHAPS). The supernatant, after centrifugation at 100,000 x g, was shown to contain molecules with binding sites for both 3Hpirenzepine (3H-pZ) and 3H-(--) quinuclidinyl benzilate (3H-QNB). Maximum binding values for 3H-PZ and 3H-QNB binding to solubilized receptors were approximately 176 4-24 pmol/g and 370 + 53 pmol/g of protein, respectively. The K d values for 3H-pZ and 3H-QNB binding to solubilized receptors were 27+6.3nM and 0.17+0.03nM, respectively. The rank order of potencies of muscarinic drugs, in terms of their ability to inhibit binding of either 3H-pZ or 3H-QNB, was atropine > pirenzepine > oxotremorine > carabachol. Pirenzepine inhibited 3H-QNB binding with a Hill coefficient of 0.77, but inhibited 3H-pZ with a Hill coefficient of 0.94. Hill coefficients for agonists were less than 1. These findings indicate that muscarinic receptors solubilized from rat brain cortex retain their abilities to interact selectively with muscarinic receptor agonists and antagonists.
Muscarinic m4 receptor activation by some atypical antipsychotic drugs
European Journal of Pharmacology, 1997
To clarify the findings that clozapine is both a muscarinic receptor agonist and antagonist, we examined the effects of neuroleptics on Ž . forskolin-stimulated cAMP accumulation in Chinese hamster ovary cells expressing human muscarinic m4 receptors CHO-hm4 and in rat striatum. With CHO-hm4 cells, clozapine induced a concentration-dependent and atropine-sensitive inhibition on cAMP formation, with EC s 60 nM and E s 74% of carbachol maximum. Other atypical neuroleptics, fluperlapine, tenilapine and olanzapine, were 50 max Ž . similar but less potent, while risperidone, rilapine, quetiapine ICI 204,636 , sertindole, and ziprasidone had almost no effect. Typical neuroleptics, haloperidol, chlorpromazine, fluphenazine, thiothixene, thioridazine, and molindone, showed either no effect or an atropine-resistant inhibition of cAMP formation. However, in rat striatal tissues, clozapine, up to 10 mM, did not show a significant inhibition of cAMP formation, probably due to a relatively low abundance of muscarinic m4 receptors and the presence of multiple types of muscarinic and other receptors, with which clozapine interacts. Nevertheless, muscarinic m4 receptor agonism, to some extent, may be a relevant mechanism for the therapeutic efficacy and side effects of clozapine and some atypical neuroleptics.
Functional and direct binding studies using subtype selective muscarinic receptor antagonists
British Journal of Pharmacology, 1988
Muscarinic receptor antagonists were examined in direct binding studies on guinea-pig cardiac and cortical muscarinic receptors. Pirenzepine, dicyclomine and hexahydroadiphenine were shown to be selective ligands for the putative M,-muscarinic receptor. 2 Functional affinity estimates of the muscarinic ligands studied was determined from their ability to inhibit carbachol-stimulated inositol phosphate (IP) accumulation in guinea-pig cortical slices. 3 The affinity estimates for the inhibition of muscarinic agonist-stimulated IP accumulation were better correlated with affinity estimates obtained from binding studies on the M, than the M2 muscarinic receptor. 4 These data provide additional evidence, both from direct binding and functional studies, for the presence of M, and M2 muscarinic receptor subtypes.
Biomedical Research, 1989
Muscarinic acetylcholine receptors purified from porcine cerebrum (predominantly M1 subtype) and porcine atrium (M2 subtype) showed essentially the same affinity for any given antagonist, including pirenzepine. This is in contrast with the difference in the affinity for pirenzepine between cerebral and atrial receptors in native membranes, and with that between mAChR I (M1) and mAChR II (M2) receptor subtypes expressed in Xenopus oocytes. Purified atrial receptors showed heterogeneous affinities for acetylcholine but a single homogeneous affinity for oXotremorine, pilocarpine and carbachol, in contrast with purified cerebral receptors, which showed heterogeneous affinities for all these agonists. The dissociation constants for the binding of acetylcholine with high-and low-affinity sites in atrial receptor preparations were essentially the same as those in the cerebral receptors; dissociation constants for the binding of oxotremorine, pilocarpine and carbachol with atrial receptors were similar to those in the low-affinity sites of cerebral receptors. The affinity for carbachol of atrial receptors increased 17-fold on treatment with 5,5'-dithiobis(2-nitrobenzoic acid), and their affinities for [3H]QNB, pirenzepine and carbachol decreased on treatment with dithiothreitol, the findings which resemble the effects of these sulfhydryl agents on cerebral receptors. These results suggest that the ligand-binding domains of the M1 and M2 receptor proteins are similar to each other and are regulated by the redox state of cysteine residues common to the two proteins, but the interaction of receptor proteins with membrane components is required for their subtype-specific interaction with pirenzepine.
Evidence for Multiple Muscarinic Receptor Subtypes in Human Brain
Journal of Neurochemistry, 1984
Pirenzepine, a compound with selective anti-sites, differing both in affinity for pirenzepine and in muscarinic activity, was used to distinguish muscarinic tissue distribution. Key Words: Human brain-Muscaacetylcholine receptor subtypes in normal human brain. rink receptor subtypes-Pirenzipine-Quinuclidinyl Hill coefficients and IC,, values derived from the inhibi-benzilate. Garvey J. M. et al. Evidence for multiple mustion of specific [3H]~-quinuclidinyl benzilate receptor carinic receptor subtypes in human brain. J. Neurochem. binding suggest the presence of two muscarinic binding 43, 299-302 (1984). Evidence derived from binding studies in animal tissues has suggested that the cholinergic muscarinic receptor population may be heterogeneous. Agonist binding studies appear to distinguish three receptor sites with differing agonist affinities (Birdsall et a]., 1978). However, the interpretation of these results has remained open to question, especially since classic muscarinic antagonists failed to differentiate muscarinic receptor subpopulations. Recently, pirenzepine, a compound with selective antimuscarinic activity, has been shown to distinguish different subclasses of muscarinic receptors in rat brain (Hammer et al., 1980). Furthermore, there appeared to be no correlation between the subclasses defined by pirenzepine and those distinguished by agonists (Birdsall et al., 1980).
Molecular Brain Research, 1987
Pirenzepine inhibition of [3H]N-methylscopolamine ([3H]NMS) binding was studied in membranous, digitonin-solubilized, and partially purified muscarinic receptors from bovine cortex, an area of the brain rich in the putative M~ muscarinic receptor subtype, and from pons-medulla, an area rich in the putative M 2 subtype. In accord with previous work, we found that pirenzepine bound to membranous receptors from cortex with an IC50 that was over one order of magnitude lower than to receptors from pons-medulla. After digitonin solubilization, however, this regional selectivity was significantly reduced. In receptors from pons-medulla, the IC50 for pirenzepine inhibition of [3H]NMS was reduced from 2.1 + 0.7 × 10-6 M in membrane-bound receptors, to 4.3 + 0.3 × 10-7 M after solubilization, whereas in receptors from cortex, the IC50 remained unchanged after solubilization. The solubilized receptors from both brain areas maintained their binding characteristics after partial purification over an ABT-Sepharose affinity column and a hydroxylapetite column. These findings raise the possibility that the different pirenzepine binding characteristics used to define M~ and M 2 receptor subtypes are not inherent in the receptor protein itself, but may be due to coupling factors such as effector proteins, phospholipids or cytoskeletal proteins which could be associated with the membranous receptor and become dissociated from the receptor after solubilization.
Mapping muscarinic receptors in human and baboon brain using [N-11C-methyl]-benztropine
Synapse, 1990
The muscarinic cholinergic system has been mapped in vivo in human and baboon brain using [N-llC-methyl]-benztropine and high resolution positron emission tomography (PET). [N-llC-methyl]-benztropine uptake was observed in frontal, parietal, occipital, and temporal cortices as well as in subcortical structures including the corpus striatum and thalamus. Uptake continued to increase in baboon and human brain in all areas over an 80 minute experimental period with the exception of the cerebellum where the accumulation of radioactivity began to decrease by 25 minutes postinjection. The ratio of incorporation of [N-llC-methyll-benztropine between corpus striatuml cerebellum was 1.53 and 1.46 in humans and baboons, respectively, at 60 minutes. Blocking studies in baboons using the muscarinic cholinergic antagonists scopolamine and benztropine and the muscarinic cholinergic agonist pilocarpine combined with blocking studies in humans using benztropine indicate that the binding of this compound is specific for the muscarinic cholinergic system. Pretreatment with the potent dopamine reuptake blocker nomifensine produced no effect on the incorporation of radioactivity in any baboon brain region examined. Analysis of labelled plasma metabolites indicates that in humans, the rate of metabolism of [N-llC-methyll-benztropine is slow (83.0% unchanged at 30 minutes postinjection) differing quite dramatically from the rate of metabolism observed in baboons (43.4% unchanged at 30 minutes postinjection). These data combined with postmortem studies in humans and primates demonstrate that [N-llC-methyll-benztropine is a suitable muscarinic cholinergic ligand for use in humans and baboons with PET