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Biomedical subjects

C Gavach

Publications and source records attributed to C Gavach.

16 recordsLinked to original sources
PubMed1987

Potential study of basement membrane.

The membrane potential of a basement membrane (bovine-anterior-lens-capsule) was studied by use of the Gibbs-Donnan systems. The T.M.S. (Teorell, Meyer, Sievers) theory was applied to these systems for the treatment of experimental data. The results show that, in the basement membrane, the density of fixed charges such as ionogenic groups encountered in heparan sulfate proteoglycan is low. The ratios of the mobilities from the chloride anion and the alkaline cation are different to those in water. In this type of membrane, the mobility of Cl- is higher than the mobilities of K+, Na+ and Ca2+. This result leads us to investigate further the diffusion problem of electrolytes through basement membrane.

Animals↗
PubMed1986

Analysis of the ion transfer through the channel of 9,11,13,15-phenylalanylgramicidin A.

The behavior of an analogue of gramicidin A in which all four tryptophanyl residues are substituted by phenylalanyl and which shows a strong voltage effect on the single channel conductance is analyzed on the basis of a 'three-barrier--two-site' model. It is shown that in the gramicidin family the side chains of some amino acids, in spite of their location, which point outside the channel can play a major role in the binding of ions in the channel and thus can significantly modify the energy profile of the channel.

Biological Transport↗
PubMed1985

Transport of potassium ions across planar lipid membranes by the antibiotic, grisorixin: I. The equilibrium state and self-diffusion K+ fluxes.

42K+ tracer flux and steady-state conductance measurements were carried out with bilayer lipid membranes containing grisorixin, a carboxylic polyether antibiotic. When the membranes are placed between two bulk aqueous solutions of identical composition, the exchange or self-diffusion transmembrane flux of potassium is measured by a method which allows the characterization of the bilayer K+ permeability at the equilibrium state. The K+ self-diffusion flux increases with the pH in the range pH 6 to pH 9 and reaches a constant value for values above 9. This can be directly related to the increase of the surface concentration of the 1:1 complex formed by K+ and the deprotonated polyether at both bilayer membrane interfaces. The transport model initially proposed by Pressman and co-workers (Proc. Natl. Acad. Sci. USA 58:1949-1956, 1967) is again taken into consideration in the quantitative analysis of the flux data. The transmembrane transport of K+ results from the translocation of its neutral complex with grisorixin and the association-dissociation of the antibiotic with either potassium or protons taking place at both interfacial space layers while the turnover of the mobile carrier is accomplished under asymmetrical conditions by a translocation process of the acidic grisorixin. Using the data of some previous studies for mixed ionophore-lipid monolayers at the air/water interface and the present results for the self-diffusion flux measurements, it was possible to propose an evaluation of the more important parameters characterizing the transport; namely, the total surface concentration of grisorixin, the interfacial pK and the translocation rate constant of its potassium neutral complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1984

Transport of mercury compounds across bimolecular lipid membranes: effect of lipid composition, pH and chloride concentration.

The use of bimolecular lipid membranes (BLM) as model membrane allows the analysis of the transport of mercury compounds across the lipidic barriers of biological membranes. The results of flux measurements show that two mercury compounds--HgCl2 and CH3HgCl--cross the BLM but the overall permeabilities are dependent on the pH of the aqueous media, and are not apparently influenced by the different phospholipid constituents of the bilayers. On the other hand, electrical measurements show that, function of the chemical speciation, the transport of this metal is done essentially in the neutral form.

Biological Transport↗
PubMed1983

Brain proteolipids. Isolation, purification and effect on ionic permeability of membranes.

Proteolipid apoproteins have been isolated from a whole bovine brain homogenate by chloroform/methanol extraction, and fractionated by chromatography on modified (lipophilic) Sephadex, followed by ion-exchange chromatography on CM-Trisacryl. The various final, highly hydrophobic, fractions are homogeneous (sodium dodecyl sulfate/polyacrylamide gel electrophoresis). Transmembrane ion transfers were studied by 22Na + flux and electrical conductance measurements. Single channel events were observed at low protein concentrations, in particular with one of the final homogeneous apoproteolipids of molecular mass 24 kDa.

Amino Acids↗
PubMed1983

Voltage and time dependence of the conductance of planar lipid bilayers doped with colicin A.

Voltage jump studies of planar bilayers doped with colicin A revealed two classes of time and voltage dependent conductance induced by colicin A. The first type of conductance, asymmetrically voltage dependent, measured as a time dependent process, was in agreement with previously described conductances of bilayers doped with colicin A or colicin E1. The second class of conductance appeared as a voltage dependent instantaneous conductance. The significance of this new type of conductance is discussed.

Colicins↗
PubMed1983

Ca2+-gramicidin A interactions and blocking effects on the ionic channel.

From spectroscopic data (infrared, CD and 13C-NMR) it is shown that Ca2+ interacts with gramicidin A and that a head-to-head gramicidin A dimer can have two Ca2+-binding sites located near the COOH termini. On the basis of this result, we can propose an explanation for the blocking effect of Ca2+ on the transport of alkali metal ions (Cs+ and K+) through gramicidin channels. The binding of Ca2+ is competitive with the alkali metal ion binding; Ca2+ cannot cross the gramicidin channel and its binding in the channel is voltage dependent. From the proposed model, it is possible to account for the influence of the addition of Ca2+ on the single-channel limiting conductance and on the variation of the single-channel current as a function of the voltage in the presence of Cs+ or K+.

Calcium↗
PubMed1982

Transport of Na+ by monensin across bimolecular lipid membranes.

Transmembrane 22Na fluxes across bimolecular lipid membranes are measured under two different experimental conditions: (a) the pH is the same in the two bulk aqueous solutions on either side of the membrane while the concentrations of Na+ are different; (b) the concentration of Na+ are identical but pH of the two solutions are different. In this latter case, the transport of Na+ occurs in the opposite direction to the difference of the proton concentration. In both cases, the electrical charge flux in negligible. A transport model is proposed to account for the experimental data.

Biological Transport, Active↗
PubMed1981

Transmembrane electrical potential of excitable membranes: a pore analysis influence of surface charges and surface dipoles.

A treatment is proposed in order to establish the general expression of the zero-current transmembrane potential of excitable membranes. The membrane model considered here is that of a hydrocarbon layer which is impermeable to ions and which represents the lipid bilayer matrix. In this matrix are incorporated ionic channels. The ion transport process through the channels is described by the absolute-rate theory applied to pores which are seen as chains of potential energy maxima and minima. Only one of the energy barriers corresponds to the gate step, and it is strongly dependent on the transmembrane potential. The kinetic equation is related to the zero current, to electrostatic boundary conditions and to the Gouy-Chapman equation for the aqueous diffuse layer.

Animals↗
PubMed1980

Photocurrent response of bacteriorhodopsin adsorbed on bimolecular lipid membranes.

The photo response of bacteriorhodopsin adsorbed on a bimolecular lipid membrane has been investigated using short-circuit current measurements. The results revealed a biphasic current vs. time curve for the photocurrent at pH values of approx. 7. This phenomenon could be modified by altering either the value of the external applied electrical field or the proton concentration differences. The observed effects of the external applied voltage, pH gradient and lipophilic proton carriers enabled us to conclude that the bacteriorhodopsin can be adsorbed in two different states, which give rise to a pumping effect and a flux of protons in opposite directions. A theoretical analysis of the photocycle in relation to the electrical field which acts on the proton uptake and release is proposed. The main effect of this field is to diminish the pumping rate due to the proton motive force resulting from the creation of space-charge in the vicinity of purple membrane fragments.

Bacteriorhodopsins↗
PubMed1978

The influence of pH on the conductance of lipid bimolecular membranes in relation to the alkaline ion transport induced by carboxylic carriers grisorixin, alborixin and monensin.

The influence of the pH on the stability and stoichiometry of the complexes formed by carboxylic-antibiotics such as grisorixin, alborixin and monensin with alkaline and alkaline earth cations has been investigated. The maximum values of bimolecular lipid membrane conductance are obtained with grisorixin and potassium ion. The conductance-pH curves show a very pronounced maximum in the neutral pH range. The results are analysed on the basis of a dimeric form of the ionophore in the complex and the possibility of having several charged complexes resulting from an heterogeneous reaction, the number of each complexed form depending on the pH of the bulk solutions.

Anti-Bacterial Agents↗
PubMed1976

The transport of calcium and sodium ions across bilayers induced by neutral synthetic ligands used in specific electrodes.

Neutral synthetic ligands of calcium and sodium which enter into the liquid membrane composition of the selective electrodes of these ions have been incorporated within the bilayer. The membrane conductance measured shows that each of these two ligands behave as ion carriers for calcium or sodium ions. The selectivities with respect to the other alcaline or alcaline earth ions are similar to those observed by potentiometric measurements with thick liquid membrane selective electrodes.

Barium↗
PubMed1975

Non-mediated zero voltage conductance of hydrophobic ions through bilayer lipid membranes.

A charge pulse technique applied to the study of charge transfer at metal-solution interfaces has been used to determine the capacity and the conductance of a membrane bilayer at both zero time and zero voltage. The transport of hydrophobic ions across a glycerol-monooleate bilayer (tetraphenyl borate, picrate, dipicrylamine and tetraphenyl arsonium) has been investigated by this method. A theoretical approach to the problem has been proposed based on one analogous to that used for the compact double layer at metallic electrodes.

Arsenicals↗