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Tricyclic antidepressants and mecamylamine bind to different sites in the human alpha4beta2 nicotinic receptor ion channel.

ABSTRACT: The interaction of tricyclic antidepressants with the human (h) alpha4beta2 nicotinic acetylcholine receptor in different conformational states was compared with that for the noncompetitive antagonist mecamylamine by using functional and structural approaches. The results established that: (a) [(3)H]imipramine binds to halpha4beta2 receptors with relatively high affinity (K(d)=0.83+/-0.08 microM), but imipramine does not differentiate between the desensitized and resting states, (b) although tricyclic antidepressants inhibit (+/-)-epibatidine-induced Ca(2+) influx in HEK293-halpha4beta2 cells with potencies that are in the same concentration range as that for (+/-)-mecamylamine, tricyclic antidepressants inhibit [(3)H]imipramine binding to halpha4beta2 receptors with affinities >100-fold higher than that for (+/-)-mecamylamine. This can be explained by our docking results where imipramine interacts with the leucine (position 9') and valine (position 13') rings by van der Waals contacts, whereas mecamylamine interacts electrostatically with the outer ring (position 20'), (c) van der Waals interactions are in agreement with the thermodynamic results, indicating that imipramine interacts with the desensitized and resting receptors by a combination of enthalpic and entropic components. However, the entropic component is more important in the desensitized state, suggesting local conformational changes. In conclusion, our data indicate that tricyclic antidepressants and mecamylamine efficiently inhibit the ion channel by interacting at different luminal sites. The high proportion of protonated mecamylamine calculated at physiological pH suggests that this drug can be attracted to the channel mouth before binding deeper within the receptor ion channel finally blocking ion flux.

SUBMITTER: Arias HR

PROVIDER: S-EPMC4605392 | biostudies-literature | 2010 Jun

REPOSITORIES: biostudies-literature

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Tricyclic antidepressants and mecamylamine bind to different sites in the human alpha4beta2 nicotinic receptor ion channel.

Arias Hugo R HR Rosenberg Avraham A Targowska-Duda Katarzyna M KM Feuerbach Dominik D Jozwiak Krzysztof K Moaddel Ruin R Wainer Irving W IW

The international journal of biochemistry & cell biology 20100317 6

The interaction of tricyclic antidepressants with the human (h) alpha4beta2 nicotinic acetylcholine receptor in different conformational states was compared with that for the noncompetitive antagonist mecamylamine by using functional and structural approaches. The results established that: (a) [(3)H]imipramine binds to halpha4beta2 receptors with relatively high affinity (K(d)=0.83+/-0.08 microM), but imipramine does not differentiate between the desensitized and resting states, (b) although tri ...[more]

PMID: 20223294

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Project description:BackgroundMigraine, ranked as the 7th-highest specific cause of disability worldwide, has caused an enormous burden on the economy and society. Tricyclic antidepressant (TCA) is one of the most commonly drugs for migraine prevention. However, evidence about the efficacy and tolerability of TCAs in the prophylaxis of migraine in adults is somewhat confusing.MethodsA computerized literature search of the PubMed, Embase, Cochrane, and Web of Science databases from inception to July 2016 was conducted. We reviewed all randomized controlled trials that assigned adults with a clinical diagnosis of migraine to TCAs or other treatments (placebo or other antidepressants). Reduction in migraine frequency or index and response rates to treatment were defined as the efficacy outcomes. Rates of dropout due to adverse effects were defined as the tolerability outcomes.ResultsIn total 12 trials consisting of 1006 participants were identified: 9 trials compared TCAs with placebo, and the other 3 compared amitriptyline with selective serotonin reuptake inhibitors (SSRIs) or serotonin norepinephrine reuptake inhibitors (SNRIs). A significant advantage of TCAs compared with placebo in the prevention of migraine in adults was observed (standardized mean difference [SMD] = -.75; 95% confidence interval [CI] = -1.05 to -.46; P?<?.00001). Participants receiving TCAs were more likely to experience an ?50% reduction in their headache burden than those receiving placebo (risk ratio [RR] =1.40; 95% CI = 0.89-2.20; P?=?.14). In addition, the efficacy between amitriptyline and SSRIs or SNRIs did not differ for migraine prevention in adults (SMD = -.01; 95% CI = -0.31 to 0.28; P?=?.94) based on the available limited trials. However, TCAs were less well tolerated than placebo (RR = 1.73; 95% CI = 1.00-2.99; P?=?.05) and SSRI or SNRI (RR = 2.85; 95% CI = 0.97-8.41; P?=?.06) on account of adverse events.ConclusionsThis research reveals that TCAs were more effective than placebo, but no more than SSRI or SNRI in ameliorating the headache burden in adults with migraine. However, TCAs appeared to be less tolerated than placebo and SSRIs or SNRIs for some side effects.

Project description:The neuronal alpha4beta2 nicotinic acetylcholine receptor (nAChR) is one of the most widely expressed nAChR subtypes in the brain. Its subunits have high sequence identity (54 and 46% for alpha4 and beta2, respectively) with alpha and beta subunits in Torpedo nAChR. Using the known structure of the Torpedo nAChR as a template, the closed-channel structure of the alpha4beta2 nAChR was constructed through homology modeling. Normal-mode analysis was performed on this closed structure and the resulting lowest frequency mode was applied to it for a "twist-to-open" motion, which increased the minimum pore radius from 2.7 to 3.4 A and generated an open-channel model. Nicotine could bind to the predicted agonist binding sites in the open-channel model but not in the closed one. Both models were subsequently equilibrated in a ternary lipid mixture via extensive molecular dynamics (MD) simulations. Over the course of 11 ns MD simulations, the open channel remained open with filled water, but the closed channel showed a much lower water density at its hydrophobic gate comprised of residues alpha4-V259 and alpha4-L263 and their homologous residues in the beta2 subunits. Brownian dynamics simulations of Na+ permeation through the open channel demonstrated a current-voltage relationship that was consistent with experimental data on the conducting state of alpha4beta2 nAChR. Besides establishment of the well-equilibrated closed- and open-channel alpha4beta2 structural models, the MD simulations on these models provided valuable insights into critical factors that potentially modulate channel gating. Rotation and tilting of TM2 helices led to changes in orientations of pore-lining residue side chains. Without concerted movement, the reorientation of one or two hydrophobic side chains could be enough for channel opening. The closed- and open-channel structures exhibited distinct patterns of electrostatic interactions at the interface of extracellular and transmembrane domains that might regulate the signal propagation of agonist binding to channel opening. A potential prominent role of the beta2 subunit in channel gating was also elucidated in the study.

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Tricyclic antidepressants and mecamylamine bind to different sites in the human alpha4beta2 nicotinic receptor ion channel.

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Tricyclic antidepressants and mecamylamine bind to different sites in the human alpha4beta2 nicotinic receptor ion channel.

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