Mode of cembranoid action on embryonic muscle acetylcholine receptor

Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.
Journal of Neuroscience Research (Impact Factor: 2.59). 01/2008; 86(1):93-107. DOI: 10.1002/jnr.21468
Source: PubMed


The mechanism of eupalmerin acetate (EUAC) actions on the embryonic muscle nicotinic acetylcholine receptor (nAChR) in BC3H-1 cells was studied by using whole-cell and single-channel patch-clamp current measurements. With whole-cell currents, EUAC did not act as an agonist on this receptor. Coapplication of 30 microM EUAC with 50 microM, 100 microM, or 500 microM carbamoylcholine (CCh) reversibly inhibited the current amplitude, whereas, with 20 microM CCh, current was increased above control values in the presence of EUAC. EUAC concentration curves (0.01-40 microM) obtained with 100 microM and 500 microM CCh displayed slope coefficients, n(H), significantly smaller than one, suggesting that EUAC bound to several sites with widely differing affinities on the receptor molecule. The apparent rate of receptor desensitization in the presence of EUAC and CCh was either slower than or equal to that obtained with CCh alone. The major finding from single-channel studies was that EUAC did not affect single-channel conductance or the ability of CCh to interact with the receptor. Instead, EUAC acted by increasing the channel closing rate constant. The results are not consistent with the competitive model for EUAC inhibition, with the sequential open-channel block model, or with inhibition by increased desensitization. The data are best accounted for by a model in which EUAC acts by closed-channel block at low concentrations, by positive modulation at intermediate concentrations, and by negative allosteric modulation of the open channel at high concentrations.

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    • "The maximum current amplitude is proportional to the density of open channels. As receptor desensitization may occur while the ligand solution is equilibrating with the cell surface, observed current amplitudes are corrected for desensitization using the equation [33], [35]: "
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    PLoS ONE 07/2013; 8(7):e67194. DOI:10.1371/journal.pone.0067194 · 3.23 Impact Factor
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    • "Such decay occurs due to receptor desensitization. Current decay phase was fit to the following equation (Ulrich et al. 2008): "
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    ABSTRACT: Nitrosamines are well known for their carcinogenic potential. Recently, it was found that some of them may also interact with human nicotinic acetylcholine receptor (nAChR) subtypes. This work studied the effects of N-nitrosonornicotine (NNN) on recombinant rat α3β4 nAChR in HEK cells as well as on nAChR endogenously expressed in PC12 pheochromocytoma cells and in BC3H1 muscle-type cells. Whole-cell recording in combination with the cell-flow technique for agonist and inhibitor application in the millisecond time region revealed that NNN inhibits the activity of neuronal nAChR expressed in HEK or PC12, whereas weak inhibitory effects on muscle-type nAChR were observed at NNN concentrations up to 3 mM. Pharmacological actions of NNN and the inhibition mechanism were studied in detail using recombinant α3β4 nAChR expressed in HEK cells as a model. NNN-induced inhibition of nicotine-evoked α3β4 nAChR activity was dose-dependent with an inhibitory constant (IC(50)) of 0.92 ± 0.05 mM. Analysis based on mathematical models indicated a noncompetitive inhibition mechanism of the rat α3β4 nAChR by NNN. NNN's mechanism of action involves acceleration of conversion of the receptor from active to desensitized forms. In summary, this work shows that NNN inhibits rat α3β4 nAChR in a noncompetitive way and interacts weakly with muscular nAChR.
    Journal of Molecular Neuroscience 07/2012; 49(1). DOI:10.1007/s12031-012-9859-5 · 2.34 Impact Factor
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    • "Taken together, these results suggest that stimulation of the nicotinic–cholinergic system reduce planarian motility, while the suppression of muscarinic cholinergic activity increases motility. The hypokinesia induced by 20 μM 4R-cembranoid could be explained by cholinergic activation, since under certain conditions 4R-cembranoid acts as a positive modulator of nicotinic receptors (Ulrich et al., 2008). "
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