Biomedical subjects

S Schreier

Publications and source records attributed to S Schreier.

At least 19 recordsLinked to original sources

PubMed2006

Structural and functional characterization of a recombinant sticholysin I (rSt I) from the sea anemone Stichodactyla helianthus.

Sticholysins I and II (Sts I and II) are two potent cytolysins from the sea anemone Stichodactyla helianthus. These isoforms present 13 substitutions, with three non-conservative located at the N-terminus. St II is considerably more hemolytic than St I in human red blood cells, a result explained by the smaller number of negatively charged groups present at St II's N-terminus. In the present work, we have obtained a recombinant St I (rSt I), differing from the wild type in a single amino acid residue (E16Q). This pseudo-wild type is structurally similar to St I and shows a similar capacity to interact with and form pores in model membranes. This was assessed by the intrinsic fluorescence increase in the presence of liposomes, their adsorption to bilayers (measured by SPR), their concentration at the air-water interface, their interaction with lipid monolayers and their capacity to promote the release of carboxyfluorescein entrapped in liposomes. In spite of these similarities, rSt I presents a larger hemolytic activity in human red blood cells than St I, being intermediate in activity between Sts I and II. The results obtained in the present work emphasize that even the change of one single E by Q at the N-terminal segment may modify the toxin HA and show that this functional property is the most sensitive to subtle changes in the protein primary structure.

Amino Acid Sequence↗

PubMed2004

Size effects on reactivity of Pt nanoparticles in CO monolayer oxidation: the role of surface mobility.

In the present paper we study the reactivity of model Pt nanoparticles supported on glassy carbon. The particle size effect is rationalized for CO monolayer oxidation exploring electrochemical methods (stripping voltammetry and chronoamperometry) and modelling. Significant size effects are observed in the particle size interval from ca. 1 to 4 nm, including the positive shift of the CO stripping peak with decreasing particle size and a pronounced asymmetry of the current transients at constant potential. The latter go through a maximum at low COads conversion and exhibit tailing, which is the longer the smaller the particle size. Neither mean field nor nucleation & growth models give a coherent explanation of these experimental findings. We, therefore, suggest a basic model employing the active site concept. With a number of reasonable simplifications a full analytical solution is obtained, which allows a straightforward comparison of the theory with the experimental data. A good correspondence between experiment and theory is demonstrated. The model suggests restricted COads mobility at Pt nanoparticles below ca. 2 nm size, with the diffusion coefficient strongly dependent on the particle size, and indicates a transition towards fast diffusion when the particle size exceeds ca. 3 nm. Estimates of relevant kinetic parameters, including diffusion coefficient, reaction constant etc. are obtained and compared to the literature data for extended Pt surfaces.

Journal Article↗

PubMed2003

Effects of sodium dodecyl sulfate on the conformation and hemolytic activity of St I and St II, two isotoxins purified from Stichodactyla helianthus.

The effect of sodium dodecyl sulfate (SDS) upon the conformation and hemolytic activity of St I and St II strongly depends on its concentration. At relatively low surfactant concentrations (ca. 0.5-5mM range) the surfactant leads to the formation of aggregates, as suggested by the turbidity observed even at relatively low (micromolar range) protein concentrations. In this surfactant range, the proteins show an increase in intrinsic fluorescence intensity and reduced quenching by acrylamide, with an almost total loss of its hemolytic activity. At higher surfactant concentrations the protein adducts disaggregates. This produces a decrease in fluorescence intensity, increase in quenching efficiency by acrylamide, loss of the native tertiary conformation (as reported by the near UV-CD spectra), and increase in alpha-helix content (as evidenced by the far UV-CD spectra). However, and in spite of these substantial changes, the toxins partially recover their hemolytic activity. The reasons for this recovering of the activity at high surfactant concentrations is discussed.

Animals↗

PubMed2002

Synthesis and pharmacological properties of TOAC-labeled angiotensin and bradykinin analogs.

Angiotensin II (AngII) and bradykinin (BK) derivatives containing the TOAC (2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid) spin label were synthesized by solid phase methodology. Ammonium hydroxide (pH 10, 50 degrees C, l h) was the best means for reverting nitroxide protonation occurring during peptide cleavage. EPR spectra yielded rotational correlation times for internally labeled analogs that were nearly twice as large as those of N-terminally labeled analogs. Except for TOAC(1)-AngII and TOAC(0)-BK, which showed high intrinsic activities, other derivatives were inactive in smooth muscle preparations. These active paramagnetic analogs may be useful for conformational studies in solution and in the presence of model and biological membranes.

Ammonium Hydroxide↗

PubMed2002

Effect of a zwitterionic surfactant (HPS) on the conformation and hemolytic activity of St I and St II, two isotoxins purified from Stichodactyla helianthus.

N-hexadecyl-N-N'-dimethyl-3-ammonio-1-propane-sulfonate (BPS) is a zwitterionic surfactant that readily binds to sticholysins I and II, two sea toxins isolated from Stichodactyla helianthus. The binding constants, evaluated from changes in fluorescence intensities elicited by the surfactant, are approximately 0.5-0.7 microM(-1). The binding of the surfactant changes the conformation of the tertiary protein, without significant changes in its secondary structure, as reported from far-ultraviolet circular dichroism spectra. The changes elicited by HPS lead to loss of the native conformation (as reported from near-ultraviolet circular dichroism spectra) and to a shift of the intrinsic protein fluorescence toward longer wavelengths, an increase in fluorescence intensities and lifetimes, and a faster quenching by acrylamide. All these changes are indicative of a more expanded tertiary conformation. Despite this, the toxins fully retain their hemolytic activities, indicating that spectroscopic changes can be poor predictors of toxin activity.

Animals↗

PubMed2001

Local anesthetic-induced microscopic and mesoscopic effects in micelles. A fluorescence, spin label and SAXS study. Single angle X-ray scattering.

The interaction of the local anesthetic tetracaine (TTC) with anionic sodium lauryl sulfate (SLS) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonio)propanesulfonate (HPS) micelles was investigated by fluorescence, spin labeling EPR and small angle X-ray scattering (SAXS). Fluorescence pH titrations allowed the choice of adequate pHs for the EPR and SAXS experiments, where either charged or uncharged TTC would be present. The data also indicated that the anesthetic is located in a less polar environment than its charged counterpart in both micellar systems. EPR spectra evidenced that both anesthetic forms increased molecular organization within the SLS micelle, the cationic form exerting a more pronounced effect. The SAXS data showed that protonated TTC causes an increase in the SLS polar shell thickness, hydration number, and aggregation number, whereas the micellar features are not altered upon incorporation of the uncharged drug. The combined results suggest that the electrostatic interaction between charged TTC and SLS, and the intercalation of the drug in the micellar polar region induce a change in molecular packing with a decrease in the mean cross-sectional area, not observed when the neutral drug sinks more deeply into the micellar hydrophobic domain. In the case of HPS micelles, the EPR spectral changes were small for the charged anesthetic and the SAXS data did not evidence any change in micellar structure, suggesting that this species protrudes more into the aqueous phase due to the lack of electrostatic attractive forces in this system.

Anesthetics, Local↗

PubMed2001

Effect of pH on the conformation, interaction with membranes and hemolytic activity of sticholysin II, a pore forming cytolysin from the sea anemone Stichodactyla helianthus.

Sticholysin II (St II) is a pore forming cytolysin obtained from the sea anemone Stichodactyla helianthus. Incubation of diluted St II solutions at different pHs (ranging from 2.0 to 12) slightly changes the secondary structure of the protein. These changes are particularly manifested at high pH. Similarly, the intrinsic fluorescence of the protein indicates a progressive opening of the protein structure when the pH increases from acidic (2.0) to basic (12). These modifications are only partially reversible and do not produce any significant increase in the small capacity of the protein to bind hydrophobic dyes (ANS or Prodan). Experiments carried out with model membranes show a reduced capacity of binding to egg phosphatidyl choline:sphingomyelin (1:1) liposomes both at low (2.3) and high (11.5) pH. Preincubation of the protein in the 2. 5-9.0 pH range does not modify its hemolytic activity, measured in human red blood cells at pH 7.4. On the other hand, preincubation at pH 11.5 drastically reduces the hemolytic activity of the toxin. This strong reduction takes place without measurable modification of the toxin ability to be adsorbed to the red blood cell surface. This indicates that preincubation at high pH irreversibly reduces the capacity of the toxin to form pores without a significant decrease in its binding capacity. The present results suggest that at pH > or = 10 St II experiences irreversible conformational changes that notably reduce its biological activity. This reduced biological activity is associated with a partial defolding of the protein, which seems to contradict what is expected in terms of a molten globule formalism.

Animals↗

PubMed2001

Properties of St I and St II, two isotoxins isolated from Stichodactyla helianthus: a comparison.

Sticholysins I and II are two highly hemolytic polypeptides purified from the Caribbean Sea anemone Stichodactyla helianthus. Their high sequence homology (93%) indicates that they correspond to isoforms of the same hemolysin. The spectroscopic measurements show a close similarity in the secondary structure content, conformation and stability of both toxins. Exposure of the toxins to high pHs (>11), a free radical source (AAPH), urea or temperature produce permanent changes in the toxin that lead to a significant loss of HA. It is significant to note that this loss of hemolytic activity occurs when other indicators, probably with the only exception of near-UV CD spectra, barely detect changes in the protein structure. This emphasizes the sensitivity of the protein function to changes in the macromolecule conformation. The most noticeable difference between both toxins is the considerably higher activity of St II, both measured in terms of erythrocyte internal K(+) exit or hemolysis; which is related to enthalpic factors. This difference is not due to an incomplete association of St I to the membrane. We consider then that the different pore forming capacity of both toxins in erythrocytes can be explained in terms of the difference in charge of the N-terminal fragment, than can considerably reduce the St I insertion rate in the membrane probably due to the negatively charged outer leaflet of the red blood cell, without a significant reduction of its capacity to bind to the cell membrane. This electrostatic effect, together with a slightly more relaxed structure in St II, could explain the higher pore forming capacity of St II in the red blood cell membrane.

Amidines↗

PubMed2001

Fmoc-POAC: [(9-fluorenylmethyloxycarbonyl)-2,2,5,5-tetramethylpyrrolidine-N-oxyl-3-amino-4-carboxylic acid]: a novel protected spin labeled beta-amino acid for peptide and protein chemistry.

The stable free radical 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (TOAC) is the only spin labeled amino acid that has been used to date to successfully label peptide sequences for structural studies. However, severe difficulty in coupling the subsequent amino acid has been the most serious shortcoming of this paramagnetic marker. This problem stems from the low nucleophilicity of TOAC's amine group towards the acylation reaction during peptide chain elongation. The present report introduces the alternative beta-amino acid 2,2,5,5-tetramethylpyrrolidine-N-oxyl-3-amino-4-carboxylic acid (POAC), potentially useful in peptide and protein chemistry. Investigations aimed at addressing the stereochemistry of this cyclic molecule through X-ray diffraction measurements of crystalline and bulk samples revealed that it consists only of the trans conformer. The 9-fluorenylmethyloxycarbonyl group (Fmoc) was chosen for temporary protection of the POAC amine function, allowing insertion of the probe at any position in a peptide sequence. The vasoactive octapeptide angiotensin II (All, DRVYIHPF) was synthesized by replacing Pro7 with POAC. The reaction of Fmoc-POAC with the peptidyl-resin occurred smoothly, and the coupling of the subsequent amino acid showed a much faster reaction when compared with TOAC. POAC7-AII was obtained in good yield, demonstrating that, in addition to TOAC, POAC is a convenient amino acid for the synthesis of spin labeled peptide analogues. The present findings open the possibility of a wide range of chemical and biological applications for this novel beta-amino acid derivative, including structural investigations involving its differentiated bend-inducing characteristics.

Amino Acids↗

PubMed2000

Surface active drugs: self-association and interaction with membranes and surfactants. Physicochemical and biological aspects.

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to self-associate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug-membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug-membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.

Cell Membrane↗

PubMed1999

Ca2+-induced increased lipid packing and domain formation in submitochondrial particles. A possible early step in the mechanism of Ca2+-stimulated generation of reactive oxygen species by the respiratory chain.

Ca2+ and P(i) accumulation by mitochondria triggers a number of alterations leading to nonspecific increase in inner membrane permeability [Kowaltowski, A. J., et al. (1996) J. Biol. Chem. 271, 2929-2934]. The molecular nature of the membrane perturbation that precedes oxidative damage is still unknown. EPR spectra of spin probes incorporated in submitochondrial particles (SMP) and in model membranes suggest that Ca(2+)-cardiolipin (CL) complexation plays an important role. Ca(2+)-induced lipid domain formation was detected in SMP but not in mitoplasts, in SMP extracted lipids, or in CL-containing liposomes. The results were interpreted in terms of Ca2+ sequestration of CL tightly bound to membrane proteins, in particular the ADP-ATP carrier, and formation of CL-enriched strongly immobilized clusters in lipid shells next to boundary lipid. The in-plane lipid and protein rearrangement is suggested to cause increased reactive oxygen species production in succinate-supplemented, antimycin A-poisoned SMP, favoring the formation of carbon-centered radicals, detected by EPR spin trapping. Removal of tightly bound CL is also proposed to cause protein aggregation, facilitating intermolecular thiol oxidation. Lipid peroxidation was also monitored by the disappearance of the nitroxide EPR spectrum. The decay was faster for nitroxides in a more hydrophobic environment, and was inhibited by butylated hydroxytoluene, by EGTA, or by substituting Mg2+ for Ca2+. In addition, Ca2+ caused an increase in permeability, evidenced by the release of carboxyfluorescein from respiring SMP. The results strongly support Ca2+ binding to CL as one of the early steps in the molecular mechanism of Ca(2+)-induced nonspecific inner mitochondrial membrane permeabilization.

Animals↗

PubMed1999

Structure of two fragments of the third cytoplasmic loop of the rat angiotensin II AT1A receptor. Implications with respect to receptor activation and G-protein selection and coupling.

The structural bases that render the third intracellular loop (i3) of the rat angiotensin II AT1A receptor one of the cytoplasmic domains responsible for G-protein coupling are still unknown. The three-dimensional structures of two overlapping peptides mapping the entire i3 loop and shown to differently interact with purified G-proteins have been obtained by simulated annealing calculations, using NMR-derived constraints collected in 70% water/30% trifluoroethanol solution. While the NH2-terminal half, Ni3, residues 213-231, adopts a stable amphipathic alpha-helix, extending over almost the entire peptide, a more flexible conformation is found for the COOH-terminal half, Ci3, residues 227-242. For this peptide, a cis-trans isomerization around the Lys6-Pro7 peptide bond generates two exchanging isomers adopting similar conformations, with an alpha-helix spanning from Asn9 to Ile15 and a poorly defined NH2 terminus. A quite distinct structural organization is found for the sequence EIQKN, common to Ni3 and Ci3. The data do suggest that the extension and orientation of the amphipathic alpha-helix, present in the proximal part of i3, may be modulated by the distal part of the loop itself through the Pro233 residue. A molecular model where this possibility is considered as a mechanism for G-protein selection and coupling is presented.

Amino Acid Sequence↗

PubMed1998

The role of ionic strength on the enhancement of the hemolytic activity of sticholysin I, a cytolysin from Stichodactyla helianthus.

Sticholysin I (St I) is a potent cytolytic polypeptide purified from the Caribbean sea anemone Stichodactyla helianthus. The hemolytic activity of sticholysin is potentiated by its preincubation at high ionic strengths. In the present work the mechanism of the potentiating action of the medium ionic strength on the toxin hemolytic capacity is investigated. It is suggested that preincubation with high saline concentration induces a transition of St I to a more relaxed conformation that facilitates the lytic process.

Animals↗

PubMed1998

Inhibition of membrane lipid peroxidation by a radical scavenging mechanism: a novel function for hydroxyl-containing ionophores.

In the present study we show that K+/H+ hydroxyl-containing ionophores lasalocid-A (LAS) and nigericin (NIG) in the nanomolar concentration range, inhibit Fe2+-citrate and 2,2'-azobis(2-amidinopropane) dihydrochloride (ABAP)-induced lipid peroxidation in intact rat liver mitochondria and in egg phosphatidylcholine (PC) liposomes containing negatively charged lipids--dicetyl phosphate (DCP) or cardiolipin (CL)--and KCl as the osmotic support. In addition, monensin (MON), a hydroxyl-containing ionophore with higher affinity for Na+ than for K+, promotes a similar effect when NaCl is the osmotic support. The protective effect of the ionophores is not observed when the osmolyte is sucrose. Lipid peroxidation was evidenced by mitochondrial swelling, antimycin A-insensitive O2 consumption, formation of thiobarbituric acid-reactive substances (TBARS), conjugated dienes, and electron paramagnetic resonance (EPR) spectra of an incorporated lipid spin probe. A time-dependent decay of spin label EPR signal is observed as a consequence of lipid peroxidation induced by both inductor systems in liposomes. Nitroxide destruction is inhibited by butylated hydroxytoluene, a known antioxidant, and by the hydroxyl-containing ionophores. In contrast, valinomycin (VAL), which does not possess alcoholic groups, does not display this protective effect. Effective order parameters (Seff), determined from the spectra of an incorporated spin label are larger in the presence of salt and display a small increase upon addition of the ionophores, as a result of the increase of counter ion concentration at the negatively charged bilayer surface. This condition leads to increased formation of the ion-ionophore complex, the membrane binding (uncharged) species. The membrane-incorporated complex is the active species in the lipid peroxidation inhibiting process. Studies in aqueous solution (in the absence of membranes) showed that NIG and LAS, but not VAL, decrease the Fe2+-citrate-induced production of radicals derived from piperazine-based buffers, demonstrating their property as radical scavengers. Both Fe2+-citrate and ABAP promote a much more pronounced decrease of LAS fluorescence in PC/CL liposomes than in dimyristoyl phosphatidylcholine (DMPC, saturated phospholipid)-DCP liposomes, indicating that the ionophore also scavenges lipid peroxyl radicals. A slow decrease of fluorescence is observed in the latter system, for all lipid compositions in sucrose medium, and in the absence of membranes, indicating that the primary radicals stemming from both inductors also attack the ionophore. Altogether, the data lead to the conclusion that the membrane-incorporated cation complexes of NIG, LAS and MON inhibit lipid peroxidation by blocking initiation and propagation reactions in the lipid phase via a free radical scavenging mechanism, very likely due to the presence of alcoholic hydroxyl groups in all three molecules and to the attack of the aromatic moiety of LAS.

Amidines↗

PubMed1997

Structure of the C-terminal fragment 300-320 of the rat angiotensin II AT1A receptor and its relevance with respect to G-protein coupling.

Angiotensin II AT1A receptor is coupled to G-protein, and the molecular mechanism of signal transduction is still unclear. The solution conformation of a synthetic peptide corresponding to residues 300-320 of the rat AT1A receptor, located in the C-terminal cytoplasmic tail and indicated by mutagenesis work to be critical for the G-protein coupling, has been investigated by circular dichroism (CD), nuclear magnetic resonance (NMR) and restrained molecular dynamics calculations. The CD data indicate that, in acidic water, at concentration below 0.8 mM, the peptide exists in a predominantly coil structure while at higher concentration it can form helical aggregates; addition of small amounts of trifluoroethanol induces a secondary structure, mostly due to the presence of helical elements. Using NMR-derived constraints, an ensemble of conformers for the peptide has been determined by restrained molecular dynamics calculations. Analysis of the converged three-dimensional structures indicates that a significant population of them adopts an amphipathic alpha-helical conformation that, depending upon experimental conditions, presents a variable extension in the stretch Leu6-Tyr20. An equilibrium with nonhelical structured conformers is also observed. We suggest that the capability of the peptide to modulate its secondary structure as a function of the medium dielectric constant, as well as its ability to form helical aggregates by means of intermolecular hydrophobic interactions, can play a significant role for G-protein activation.

Animals↗

PubMed1997

Effect of trivalent metal ions on phase separation and membrane lipid packing: role in lipid peroxidation.

The capacity of Al3+-related cations (Sc3+, Ga3+, In3+, Be2+, Y3+, and La3+) to promote membrane rigidification and lateral phase separation was evaluated in liposomes containing zwitterionic (phosphatidylcholine, PC) and negatively charged (phosphatidylserine, PS) phospholipids. These effects were correlated with the capacity of the ions to stimulate Fe2+-supported lipid peroxidation. A13+, Sc3+, Ga3+, In3+, Be2+, Y3+, and La3+ (50-200 microM) increased the order parameter of the fluorescent probe 1,3-diphenylhexatriene incorporated in PC:PS membranes. In addition, the electron paramagnetic resonance spectra of spin-labeled fatty acids indicated a reduction in lipid motion induced by Sc3+, Y3+, and La3+. The effect was found to extend down to carbon 16 on the acyl chain. The ions (10-200 microM) were also able to induce lateral phase separation, as evaluated from the increase in fluorescence quenching of the probe 2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl-1-hexadec anoyl-sn-glycero-3-phosphocholine. The ability of the ions to alter membrane lipid packing and induce lateral phase separation correlated in a positive manner (r2 = 0.91 and 0.90, respectively) with their capacity to stimulate the production of Fe2+-initiated 2-thiobarbituric-reactive species, a measure of lipid peroxidation. These results show that Al3+-related metal ions cause membrane rigidification and phase separation, which could affect membrane-related processes. The results support the hypothesis that ions without redox capacity can stimulate Fe2+-initiated lipid peroxidation by increasing lipid packing and by promoting the formation of rigid clusters. Both processes will bring phospholipid acyl chains closer together, thus favoring the propagation step of lipid peroxidation.

Aluminum↗

PubMed1997

Spin-labeled extracellular loop from a seven-transmembrane helix receptor: studies in solution and interaction with model membranes.

A spin-labeled pentadecapeptide was synthesized containing 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (TOAC) as the N-terminal amino acid and residues 253-266 (EYWSTFGNLHHISL) of the mass oncogene receptor, a membrane-bound protein from the G-protein coupled receptors family. According to predictions, this protein folds into seven transmembrane helices connected by three extra- and three intracellular loops, and the peptide encompasses part of the third extracellular loop and part of the seventh helix. Electron paramagnetic resonance (EPR) spectra of the spin-labeled peptide (TOAC-14) were obtained in aqueous solution as a function of pH and temperature, in a secondary structure-inducing solvent [trifluoroethanol (TFE)], and in the presence of detergent micelles and phospholipid bilayers. The charged and uncharged amino groups of TOAC and TOAC-14 yielded spectra with different isotropic hyperfine splittings (aN). The slow exchange between protonated and unprotonated forms in the EPR time scale gave rise to composite spectra weighted by the Henderson-Hasselbalch equation. Plots of aN vs pH allowed the determination of the amino group pK values (8.4 and 4.5, for TOAC and TOAC-14, respectively). A small change in aN centered at pH 6.5 was ascribed to the titration of the histidines. Values of calculated rotational correlation times were indicative of a pH-induced conformational change. A conformational change was also observed in TFE. TOAC-14 bound to micelles irrespective of peptide and detergent head group charge. In contrast, the peptide bound to phospholipid bilayers only when both carried opposite charges. The slow exchange (in the EPR time scale) between membrane-bound and free TOAC-14 allowed the calculation of the peptide's partition coefficient. The spectral line shapes were affected by aggregate size and degree of packing of the constituent molecules. It is proposed that pH, polarity, and lipid environment can affect the conformation of water-exposed regions of membrane-bound receptors, thereby playing a role in the mechanism of signal transduction.

Amino Acid Sequence↗

PubMed1996

Molecular and physicochemical aspects of local anesthetic-membrane interaction.

Local anesthesia is achieved by the binding of anesthetic molecules to the sodium channel, a membrane protein responsible for the transport of the extracellular sodium to the cytosol. Local anesthetics (LA) bind to the sodium channel inhibiting sodium transport and, as a consequence, the action potential responsible for the nervous impulse. Most LA are relatively hydrophobic ionizable amines that undergo partitioning into lipid. Both activity and toxicity correlate positively with LA hydrophobicity. Effects of LA on the structural and dynamical properties of the membrane lipid region may be responsible for some of the toxic effects caused by these molecules. The present review focuses on research done on the interaction between both the charged and uncharged forms of LA and lipid systems-bilayers and micelles. LA have been found to alter phospholipid gel to liquid crystal phase transition temperature (Tc), to affect bilayer permeability, to influence molecular packing, and to inhibit the bilayer to hexagonal phase transition. Anesthetics in micellized form disrupt bilayers giving rise to lipid-LA mixed micelle-like aggregates. The question of LA location in the bilayer is also addressed. Special emphasis is placed on work focusing on the quantitative analysis of drug binding, as well as on the effects of binding on physicochemical properties of the LA, such as extent of ionization (pK shifts) and rates of chemical reactions. The understanding of these phenomena has contributed to the development of less toxic liposomal formulations capable of prolonging the duration of anesthesia.

Anesthetics, Local↗