scholarly journals Coupling of Solute and Solvent Flows in Porous Lipid Bilayer Membranes

1971 ◽  
Vol 57 (4) ◽  
pp. 479-493 ◽  
Author(s):  
Thomas E. Andreoli ◽  
James A. Schafer ◽  
Susan L. Troutman
Keyword(s):  
Lipid Bilayer ◽  
Water Flow ◽  
Solute Flux ◽  
Lipid Bilayer Membranes ◽  
Membrane Phase ◽  
Bilayer Membranes ◽  
Osmotic Flow ◽  
Unstirred Layers ◽  
Osmotic Water ◽  
Osmotic Water Flow

The present experiments were designed to evaluate coupling of water and nonelectrolyte flows in porous lipid bilayer membranes (i.e., in the presence of amphotericin B) in series with unstirred layers. Alterations in solute flux during osmosis, with respect to the flux in the absence of net water flow, could be related to two factors: first, changes in the diffusional component of solute flux referable to variations in solute concentrations at the membrane interfaces produced by osmotic flow through the unstirred layers; and second, coupling of solute and solvent flows within the membrane phase. Osmotic water flow in the same direction as solute flow increased substantially the net fluxes of glycerol and erythritol through the membranes, while osmotic flow in the opposite direction to glycerol flow reduced the net flux of that solute. The observed effects of osmotic water flow on the fluxes of these solutes were in reasonable agreement with predictions based on a model for coupling of solute and solvent flows within the membrane phase, and considerably in excess of the prediction for a diffusion process alone.

scholarly journals An Analysis of Unstirred Layers in Series with "Tight" and "Porous" Lipid Bilayer Membranes

1971 ◽  
Vol 57 (4) ◽  
pp. 464-478 ◽  
Author(s):  
Thomas E. Andreoli ◽  
Susan L. Troutman
Keyword(s):  
Lipid Bilayer ◽  
Effective Thickness ◽  
Porous Membranes ◽  
Lipid Bilayer Membranes ◽  
Bilayer Membranes ◽  
Permeability Coefficients ◽  
Unstirred Layers ◽  
Water Permeability Coefficient ◽  
Osmotic Water ◽  
In Series

The present experiments were designed to evaluate the effective thickness of the unstirred layers in series with native and porous (i.e., in the presence of amphotericin B) lipid bilayer membranes and, concomitantly, the respective contributions of membranes and unstirred layers to the observed resistances to the diffusion of water and nonelectrolytes between aqueous phases. The method depended on measuring the tracer permeability coefficients for the diffusion of water and nonelectrolytes (PDDi, cm sec-1) when the aqueous phase viscosity (η) was increased with solutes having a unity reflection coefficient, such as sucrose or dextran. The effective thickness of the unstirred layers (αt, cm) and the true, or membrane, permeability coefficients for diffusion of water and nonelectrolytes (Pmmi, cm sec-1) were computed from, respectively, the slope and intercept of the linear regression of 1/PDDi on η. In both the native and porous membranes, αt was approximately 110 x 10-4 cm. The ratio of Pf, the osmotic water permeability coefficient (cm sec-1) to PmmH2O was 1.22 in the native membranes and 3.75 in the porous membranes. For the latter, the effective pore radius, computed from Poiseuille's law, was approximately 5.6 A. A comparison of Pmmi and PDDi, indicated that the porous membranes accounted for 16, 25, and 66% of the total resistance to the diffusion of, respectively, H2O, urea, and glycerol, while the remainder was referable to the unstirred layers.

scholarly journals Permeability of Lipid Bilayer Membranes to Organic Solutes

1968 ◽  
Vol 52 (3) ◽  
pp. 495-508 ◽  
Author(s):  
Ross C. Bean ◽  
William C. Shepherd ◽  
Hakchill Chan
Keyword(s):  
Lipid Bilayer ◽  
Lipid Composition ◽  
Solute Flux ◽  
Organic Solutes ◽  
Lipid Bilayer Membranes ◽  
Concentration Gradients ◽  
Bilayer Membranes ◽  
Solute Permeability ◽  
Lipid Organization ◽  
Interfacial Charge

A sensitive fluorescence technique was used to measure transport of organic solutes through lipid bilayer membranes and to relate permeability to the functional groups of the solute, lipid composition of the membrane, and pH of the medium. Indole derivatives having ethanol, acetate, or ethylamine in the 3-position, representing neutral, acidic, and basic solutes, respectively, were the primary models. The results show: (a) Neutral solute permeability is not greatly affected by changes in lipid composition but presence or absence of cholesterol in the membranes could greatly alter permeability of the dissociable substrates. (b) Indole acetate permeability was reduced by introduction of phosphatidylserine into membranes to produce a net negative charge on the membranes. (c) Permeability response of dissociable solutes to variation in pH was in the direction predicted but not always of the magnitude expected from changes in the calculated concentrations of the undissociated solute in the bulk aqueous phase. Concentration gradients of amines across the membranes caused substantial diffusion potentials, suggesting that some transport of the cationic form of the amine may occur. It is suggested that factors such as interfacial charge and hydration structure, interfacial polar forces, and lipid organization and viscosity, in addition to the expected solubility-diffusion relations, may influence solute flux.

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