We examined the effect of two local anesthetics (lidocaine and benzocaine) on the structure and dynamics of egg phosphatidylcholine (EPC) membranes at pH 7.4 and 10.5 in order to assess the preferred environment of these local anesthetics within the bilayer. Changes in the organization of small unilamellar vesicles were monitored by Fourier-transform infrared spectroscopy (FTIR), which revealed that the local anesthetics (LA) changed the water-molecule hydrogen-bonding pattern, monitored by effects on the acyl chain, phosphate group and glycerol carbonyl regions of the phospholipids. The effect of increasing the concentration of local anesthetic on these regions of egg phosphatidylcholine revealed that charged lidocaine increases the access of water to the phosphate groups and to carbonyls in the glycerol region of the bilayer, while uncharged lidocaine (pH 10.5) affected mainly the glycerol carbonyls. Benzocaine, on the other hand diminished the access of water molecules to the glycerol carbonyl region. A model is proposed in which charged and uncharged lidocaine binds to the lipids near the phosphate and glycerol regions of the bilayer. For benzocaine, the main locations proposed are in the glycerol region and at the first carbons of the acyl chain. We propose that this preferential positioning, demonstrated here in model phospholipid membranes, also takes place in the nerve axons, where it could modulate the access of the LA molecules to their protein-binding sites in the voltage-gated sodium channel.2712735Auger, M., Smith, I.C.P., Mantsch, H., Wong, P.T.T., High-pressure infrared study of phosphatidylserine bilayers and their interactions with the local anesthetic tetracaine (1990) Biochemistry, 29, pp. 2008-2015Auger, M., Jarrel, H.C., Smith, I.C.P., Wong, P.T.T., Siminovitch, D.J., Mantsch, H.H., Pressure-induced exclusion of a local anesthetic from model and nerve membranes (1987) Biochemistry, 26, pp. 8513-8516Blume, A., Hubner, W., Messner, G., Fourier transform infrared spectroscopy of 13C=O-labeled phospholipids hydrogen bonding to carbonyl groups (1988) Biochemistry, 27, pp. 8239-8249Boulanger, Y., Schreier, S., Leitch, L.C., Smith, I.C.P., Multiple binding sites for local anesthetics in membranes: Characterization of the sites and their equilibria by deuterium NMR of specifically deuterated procaine and tetracaine (1980) Can J Biochem, 58, pp. 986-995Boulanger, Y., Schreier, S., Smith, I.C.P., Molecular details of anesthetic-lipid interaction as seen by deuterium and phosphorus-31 nuclear magnetic resonance (1981) Biochemistry, 20, pp. 6824-6830Bradley, D.J., Richards, C.D., Temperature-dependence of the action of nerve blocking agents and its relationship to membrane-buffer partition coefficients: Thermodynamic implications for the site of action of local anaesthetics (1984) Br J Pharmacol, 81, pp. 161-167Chiou, J.S., Krishna, P.R., Kamaya, H., Ueda, I., Alcohols dehydrate lipid membranes: An infrared study on hydrogen bonding (1992) Biochim Biophys Acta, 1110, pp. 225-233Covino, B.G., Vassalo, H.G., Anestésicos locais: Mecanismos de ação e uso clínico (1985) Rio de Janeiro: Colina EditoraDe Bony, J., Dennis, E.A., Alcohols dehydrate lipid membranes: An infrared study on hydrogen bonding (1981) Biochemistry, 20, pp. 5256-5260de Paula, E., Schreier, S., Use of a novel method for determination of partition coefficients to compare the effect of local anesthetics on membrane structure (1995) Biochim Biophys Acta, 1240, pp. 25-33de Paula, E., Schreier, S., Molecular and physicochemical aspects of local anesthetic-membrane interaction (1996) Braz J Med Biol Res, 29, pp. 877-894Fraceto, L.F., de Paula, E., Anestésicos locais: Interação com membranas de eritrócito de sangue humano, estudada por ressonância magnética nuclear de 1H e 31P (2004) Quim Nova, 27, pp. 66-71Fraceto, L.F., Pinto, L.M.A., Franzoni, L., Spisni, A., Schreier, S., de Paula, E., Specific location of lidocaine in phospholipid bilayers: A 1H-NMR and RPE study (2002) Biophys Chem, 99, pp. 229-243Fraceto, L.F., Spisni, A., Schreier, S., de Paula, E., Differential effects of uncharged aminoamide local anesthetics on phospholipid bilayers, as monitored by 1H-NMR measurements (2005) Biophys Chem, 115, pp. 11-18Frezzatti Jr, W.A., Toselli, W.R., Schreier, S., Spin label study of local anesthetic-lipid membrane interactions. Phase separation of the uncharged form and bilayer micellization by the charged form of tetracaine (1986) Biochim Biophys Acta, 860, pp. 531-538Gallová, J., Balgavý, P., Interaction of local anesthetic heptacaine homologs with phosphatidylcholine bilayers: Spin label ESR study (1997) Biochim Biophys Acta, 1325, pp. 189-196Gargiulo, R.J., Giotta, G.J., Wang, H.H., Spin-labeled analogs of local anesthetics (1973) J Med Chem, 16, pp. 707-708Giotta, G.J., Chan, D.S., Wang, H.H., Binding of spin-labeled local anesthetics to phosphatidylcholine and phosphatidylserine liposomes (1974) Arch Biochim Biophys, 163, pp. 453-458Gupta, S.P., Quantitative structure-activity relationship studies on local anesthetics (1991) Chem Rev, 91, pp. 1109-1119Kaminoh, Y., Kamaya, H., Ueda, I., Differential affinity of charged local anesthetics to solid-gel and liquid-crystalline states of dimyristoylphosphatidic acid vesicle membranes (1989) Biochim Biophys Acta, 987, pp. 63-68Kaminoh, Y., Tashiro, C., Kamaya, H., Ueda, I., Membrane-buffer partition coefficients of tetracaine for liquid-crystal and solid-gel membranes estimated by direct ultraviolet spectrophotometry (1988) Biochim Biophys Acta, 946, pp. 215-220Kuroda, Y., Fujiwara, Y., Locations and dynamical perturbations for lipids of cationic forms of procaine, tetracaine, and dibucaine in small unilamellar phosphatidylcholine vesicles as studied by nuclear Overhauser effects in 1H nuclear magnetic resonance spectroscopy (1987) Biochim Biophys Acta, 903, pp. 395-410Kuroda, Y., Nasu, H., Fujiwara, Y., Nakagawa, T., Orientations and locations of local anesthetics benzocaine and butamben in phospholipid membranes as studied by 2H NMR spectroscopy (2000) J Memb Biol, 177, pp. 117-128Lee, A.G., Model for action of local anaesthetics (1976) Nature, 262, pp. 545-548Lever, M.J., Miller, K.W., Paton, W.D.M., Smith, E.B., Pressure reversal of anaesthesia (1971) Nature, 231, pp. 368-371Lochynski, S., Frackwiak, B., Librowski, T., Czarnecki, R., Grochowski, J., Serda, P., Pasenkiewicz-Gierula, M., Stereochemistry of terpene derivatives. Part 3: Hydrolytic kinectic resolution as a convenient approach to chiral aminohydroxyiminocaranes with local anaesthetic activity (2002) Tetrahedron, 13, pp. 873-878Pinto, L.M.A., (1998) Interação dos anestésicos locais benzocaína, lidocaína e tetracaína com membranas modelos, , Dissertação] Campinas: Departamento de Bioquímica, UNICAMP;Pinto, L.M.A., Yokaichiya, D.K., Fraceto, L.F., de Paula, E., Interaction of benzocaine with model membranes (2000) Biophys Chem, 87, pp. 213-223Schreier, S., Amaral, A.T., Stachissini, A.S., Bianconi, M.L., Electron spin resonance study of benzoic acid esters, analogs of local anesthetics. Interaction with membranes, aggregation and hydrolysis (1986) Bull Magn Res, 8, pp. 166-171Schreier, S., Frezzatti Jr, W.A., Araujo, P.S., Chaimovich, H., Cuccovia, I.M., Effect of lipid membranes on the apparent pK of the local anesthetic tetracaine. Spin label and titration studies (1984) Biochim Biophys Acta, 769, pp. 231-237Schoepflin, M., Fingeli, U.P., Perlia, X., A study on the interaction of local anesthetics with phospholipid model membranes by infrared ATR spectroscopy (1987) J Am Chem Soc, 109, pp. 2375-2380Seelig, A., Local anesthetics and pressure: A comparison of dibucaine binding to lipid monolayers and bilayers (1987) Biochim Biophys Acta, 899, pp. 196-204Seeman, P., Erythrocyte membrane stabilization by steroids and alcoholsa possible model for anesthesia (1966) Biochem Pharmacol, 15, pp. 1753-1766Sheetz, M.P., Chan, S., Effect of sonication on the structure of lecithin bilayers (1972) Biochemistry, 11, pp. 4573-4581Skou, J.C., Local anaesthetics. V. The action of local anaesthetics on monomolecular layers of stearic acid (1954) Acta Pharmacol Toxicol, 10, pp. 317-324Timothy, J.L., Ross, P.D., Levin, I.W., Effects of anesthetic and nonanesthetic steroids on dipalmitoylphosphatidylcholine liposomes: A calorimetric and Raman spectroscopic investigation (1984) Biochemistry, 23, pp. 4636-4641Trudell, J.R., A unitary theory of anesthesia based on lateral phase separations in nerve membranes (1977) Anesthesiology, 46, pp. 5-10Ueda, I., Chiou, J.S., Krishma, P.R., Kamaya, H., Local anesthetics destabilize lipid membranes by breaking hydration shell: Infrared and calorimetry studies (1994) Biochim Biophys Acta, 1190, pp. 421-429Wakita, M., Kuroda, Y., Fujiwara, Y., Nakagawa, T., Conformations of dibucaine and tetracaine in small unilamellar phosphatidylcholine vesicles as studied by nuclear Overhauser effects in 1H nuclear magnetic resonance spectroscopy (1992) Chem Phys Lipids, 62, pp. 45-54Wong, P.T., Siminovitch, D.J., Mantsch, H.H., Structure and properties of model membranes: New knowledge from high-pressure vibrational spectroscopy (1988) Biochim Biophys Acta, 947, pp. 139-171Yokono, S., Ogli, K., Miura, S., Ueda, I., 400 MHz two-dimensional nuclear Overhauser spectroscopy on anesthetic interaction with lipid bilayer (1989) Biochim Biophys Acta, 982, pp. 300-302