ABSTRACT
Nicotinic acetylcholine receptors (nAChRs) are involved in a great range of physiological and pathological conditions. Since they are transmembrane proteins, they interact strongly with the lipids surrounding them. Thus, the plasma membrane composition and heterogeneity play an essential role for the correct nAChR function, on the one hand, and the nAChR influences its immediate lipid environment, on the other hand. The aim of this work was to investigate in more detail the role of the biophysical properties of the membrane in nAChR function and vice versa, focusing on the relationship between Chol and nAChRs. To this end, we worked with different model systems which were treated either with (i) more Chol, (ii) cholesteryl hemisuccinate, or (iii) the enzyme cholesterol oxidase to generate different membrane sterol conditions and in the absence and presence of γTM4 peptide as a representative model of the nAChR. Fluorescence measurements with crystal violet and patch-clamp recordings were used to study nAChR conformation and function, respectively. Using confocal microscopy of giant unilamellar vesicles we probed the membrane phase state/order and organization (coexistence of lipid domains) and lipid-nAChR interaction. Our results show a feedback relationship between membrane organization and nAChR function, i.e. whereas the presence of a model of nAChRs conditions membrane organization, changing its lipid microenvironment, membrane organization and composition perturb nAChRs function. We postulate that nAChRs have a gain of function in disordered membrane environments but a loss of function in ordered ones, and that Chol molecules at the outer leaflet in annular sites and at the inner leaflet in non-annular sites are related to nAChR gating and desensitization, respectively. Thus, depending on the membrane composition, organization, and/or order, the nAChR adopts different conformations and locates in distinct lipid domains and this has a direct effect on its function.
Subject(s)
Receptors, Nicotinic , Receptors, Nicotinic/chemistry , Receptors, Nicotinic/metabolism , Membrane Lipids/metabolism , Cholesterol Oxidase/metabolism , Unilamellar Liposomes/metabolism , Gentian Violet/metabolism , Cholesterol/metabolism , Cell Membrane/metabolismSubject(s)
Antidotes/pharmacology , Mutagenesis/drug effects , Ubiquinone/pharmacology , Animals , Drug Evaluation , Male , Mice , Mice, Inbred C57BLABSTRACT
The effects of ubiquinone-10 given in oral doses of 0.2-20 mg/kg on cytogenetic effects of intraperitoneal photrinum (7 and 14 mg/kg), dioxydinum (100 and 300 mg/kg) and cyclophosphanum (20 mg/kg) were studied in the bone marrow metaphasic cells of male C57Bl/6 mice. Ubiquinone-10 (2 to 20 mg/kg) statistically significantly reduced the clastogenic action of these mutagens, except photrinum used in a dose of 7 mg/kg. The antimutagenic effect of the drug was dose-independent and no more than 50%. The findings enable ubiquinone-10 be considered as an endogenous antimutagen. It is suggested that the antimutagenic activity of the compound is due to its antioxidative properties.
