title: Spectroscopic evidence for a preferential location of lidocaine inside phospholipid bilayers.
abstract: We examined the effect of uncharged lidocaine on the structure and dynamics of egg phosphatidylcholine (EPC) membranes at pH 10.5 in order to assess the location of this local anesthetic in the bilayer. Changes in the organization of small unilamellar vesicles were monitored either by electron paramagnetic resonance (EPR)-in the spectra of doxyl derivatives of stearic acid methyl esters labeled at different positions in the acyl chain (5-, 7-, 12- and 16-MeSL)-or by fluorescence, with pyrene fatty-acid (4-, 6-, 10- and 16-Py) probes. The largest effects were observed with labels located at the upper positions of the fatty-acid acyl-chain. Dynamic information was obtained by 1H-NMR. Lidocaine protons presented shorter longitudinal relaxation times (T(1)) values due to their binding, and consequent immobilization to the membrane. In the presence of lidocaine the mobility of all glycerol protons of EPC decreased, while the choline protons revealed a higher degree of mobility, indicating a reduced participation in lipid-lipid interactions. Two-dimensional Nuclear Overhauser Effect experiments detected contacts between aromatic lidocaine protons and the phospholipid-choline methyl group. Fourier-transform infrared spectroscopy spectra revealed that lidocaine changes the access of water to the glycerol region of the bilayer. A "transient site" model for lidocaine preferential location in EPC bilayers is proposed. The model is based on the consideration that insertion of the bulky aromatic ring of the anesthetic into the glycerol backbone region causes a decrease in the mobility of that EPC region (T(1) data) and an increased mobility of the acyl chains (EPR and fluorescence data).
authors.affiliation: Departamento de Bioquímica, Instituto de Biologia/Unicamp, Instituto de Biologia, Universidade Estadual de Campinas, CP 6109, CEP 13083-970, Campinas, SP, Brazil.
authors.forename: Leonardo Fernandes
authors.initials: LF
authors.lastname: Fraceto
authors.forename: Luciana de Matos Alves
authors.initials: Lde M
authors.lastname: Pinto
authors.forename: Lorella
authors.initials: L
authors.lastname: Franzoni
authors.forename: Ataualpa Albert Carmo
authors.initials: AA
authors.lastname: Braga
authors.forename: Alberto
authors.initials: A
authors.lastname: Spisni
authors.forename: Shirley
authors.initials: S
authors.lastname: Schreier
authors.forename: Eneida
authors.initials: E
authors.lastname: de Paula
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005612:Freeze Drying; D008012:Lidocaine / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D008012:Lidocaine; D017666:Deuterium Oxide