Use of 9-aminoacridine in the evaluation of liposome surface charge density: Role of the adsorption on lipidic sites (original) (raw)
Related papers
European Biophysics Journal, 1993
A large number of surface charge density (cy) and surface potential (40) estimations have been based on 1) titrations of the fluorescence of 9-aminoacridine released from the diffuse double layer adjacent to negatively charged membrane surfaces by non-adsorbing monovalent and divalent cations, and 2) calculations using experimental data from the titration curves and the Gouy-Chapman theory of the diffuse double layer. In this paper we discuss the different simplifying approximations employed in the earlier calculations and recommend modified formulas for the calculations. The latter have been derived without any simplifying approximation concerning the ionic (electrolyte) composition of the titration assays. We also show that c~ depends, to some extent, on the concentrations of buffer and vesicles in the assays and present experimental evidence that decamethonium (decane-l,10-bis-trimethylammonium), a bulky organic divalent cation, can be satisfactorily used for the estimation of c~ under well-defined conditions, despite its putative interaction with membranes.
The Journal of Membrane Biology, 1982
port have, in the main, utilized artificial membranes, both planar and vesicular. Systems of biological interest, viz., cells and organelles, resemble vesicles in size and geometry. Methods are, therefore, required to extend the results obtained with planar membranes to liposome systems. In this report we present an analysis of a fluorescence technique, using the divalent cation probe chlortetracycline, in small, unilamellar vesicles, for the study of divalent cation fluxes. An ion carrier (X537A) and a pore former (alamethicin) have been studied. The rate of rise of fluorescence signal and the transmembrane ion gradient have been related to transmembrane current and potential, respectively. A second power dependence of ion conduction-including the electrically silent portion thereof-on X537A concentration, has been observed. An exponential dependence of "current" on "transmembrane potential" in the case of alamethicin is also confirmed. Possible errors in the technique are discussed.
Charge determination of membrane molecules in polymer-supported lipid layers
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1995
A method for two-dimensional micro-electrophoresis and charge determination of fluorescence-labeled membrane molecules in lipid layers is presented. Therefore, the labeled molecules are dissolved in a lipid monolayer which acts as a fluid matrix. The essential part of the sample preparation is an aqueous polymer film composed of agarose onto which the layer is transferred by Langmuir-Blodgett technique. The induced force of an applied electric field leads to a drift of the charged fluorescent molecules. The mobility is determined by an analysis of the steady-state bleach profile which is produced by continuous fluorescence micro-photolysis of a rectangular area of the monolayer. Testing a variety of amphiphilic molecules, measurements yielded values of zero, plus or minus one elementary net charge within a margin of error. The experimental setup described here can be used for lateral separation, enrichment and isoelectric focusing of membrane components.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1993
Liposomes of egg PC/PG (8:2, mol/mol) were multilabelled with PBFI, pyranine and oxonol VI, fluorescent probes for, respectively, K +, H + and membrane potential. Monitoring fluorescence with a multichannel photoncounting spectrofluorometer during K + filling experiments allowed to measure K ÷ influx, the associated H ÷ efflux and the membrane potential, continuously and simultaneously. The proton net efflux quantitatively mirrored the K ÷ net influx. The rate of the K÷/H + exchange diminished progressively as a quasi-equilibrium was reached for both K ÷ and H ÷. In the presence of valinomycin, the measured membrane potential during the K + filling actually corresponded to the Nernst potential calculated from the observed K + gradient. In the absence of valinomyein, it corresponded to the Nernst potential calculated from the observed H ÷ gradient. In the latter case, the permeability coefficient of liposomes to K ÷, calculated from the Goldman-Hodgkin-Katz relation, was 6.10-13 m s-1. The selectivity sequence for alkali cations of liposomes was determined from the measured H ÷ efflux associated to the influx of the different cations. The selectivity sequence corresponded to the series VI of Eisenman, suggesting interaction of the cation with an anionic field of intermediate strength.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1996
The effects of monovalent cations on the interracial electrostatic potential (t~a), hydrodynamic shear boundary distance (ds), and membrane curvature were studied in large unilamellar phospholipid and galacto/sulfolipid liposomes containing different fractions of negatively charged lipids. The differential effects of alkali metal ions on ~Jd could be accurately determined at physiological surface charge densities with a surface-anchored fluorescent probe. Li + and Na + more effectively decrease ~d and exhibit higher association constants (K,s) than K + and Cs +. These two groups of cations display qualitatively different perturbations of the interfacial structure. Combining Ka~ values with the electrokinetic (~) potentials yielded the respective d~ values. At low ionic strength ds more substantially increases with Li + or Na ÷ than with K + or Cs +. Increasing surface charge density causes increased membrane curvature in the presence of K + or Cs +, but this is largely prevented by Li + or Na +. Membrane binding of the amphiphilic cation acridine orange decreases surface charge and membrane curvature more extensively than H3 O+, Li +, and Na +. The differential interface-perturbing behavior of monovalent cations is discussed with regard to their different hydration tendencies that will modulate the extent and stability of the hydrogen-bond network along the charged membrane surface.
General physiology and biophysics, 1992
The effects of fluorescent probes 9-aminoacridine (9AA) and atebrine (AT) on physical properties of liposomes and planar bilayer lipid membranes (BLM) were studied. The method of fluorescence spectroscopy and the electrostriction method based on measurement of higher current harmonics were used. At low concentrations (10(-5)-5 x 10(-5) mol/l), 9AA increased fluorescence intensity, while in liposomes from soybean phosphatidylcholine fluorescence quenching occurred at higher probe concentration. Fluorescence quenching occurred over the entire concentration range tested (10(-5)-10(-4) mol/l) in liposomes made from a mixture of egg phosphatidylcholine and cardiolipin. In contrast to 9AA, AT, thanks to its hydrophobic chain, penetrates deeper into the hydrophobic membrane moiety; thus, immobilization of the molecule and an increase in fluorescence intensity was always observed. Probes adsorbed to membranes, leaving their electric capacitance effectively unchanged. Adsorption of charged d...
The Electrochemistry of Liposomes
Israel Journal of Chemistry, 2008
This review aims to summarize the current state of research concerning the interaction of electrodes with liposomes suspended in solutions. Main attention is given to the complex mechanism of adhesion and spreading of liposomes on mercury electrodes. That mechanism can be studied with the help of chronoamperometry, where each adhesion-spreading event appears as a capacitive current spike. Integration of these spikes produces charge versus time transients that can be modeled and simulated, revealing the details of the multi-step adhesion-spreading process. Whereas the number of spikes per time mirrors the macro-kinetics, the analysis of the time behavior of each spike mirrors the micro-kinetics of each adhesion-spreading event. The reviewed studies show that this approach provides a new tool to study the properties of liposome membranes. The adhesion-spreading of liposomes on mercury electrodes has strong similarities to the process of vesicle fusion, which makes these studies a biomimetic model allowing one to deduce the effects of foreign molecules in bilayer membranes.
Biophysical Journal, 2001
Second harmonic generation (SHG) was used to study both the adsorption of malachite green (MG), a positively charged organic dye, onto liposomes of different lipid compositions, and the transport kinetics of MG across the liposome bilayer in real time. We found that the dye adsorption increased linearly with the fraction of negatively charged lipids in the bilayer. Similarly, the transport rate constant for crossing the bilayer increased linearly with the fraction of charged lipid in the bilayer.