Glucose permeability coefficient

The permeability of solutes across lipid bilayers is a product of the partition coefficient and the transverse diffusion coefficient [30]. Bilayer polymerization can alter solute diffusion by modifying either or both of these processes. In order to examine the effect of polymerization on bilayer permeability a nonionic solute of moderate permeability, [3H-glucose], was encapsulated in the vesicles prior to polymerization, removed from the exterior after polymerization, and its permeation across the bilayer was measured periodically [31]. Quantitative measurements of the 3H-glucose leakage revealed that the formation of linear polymer chains from methacryloyl lipids reduced the permeability coefficient to 0.3 to 0.5 of that of the unpolymerized lipid vesicles. A larger reduction (two orders of magnitude) was only found when crosslinked polymer networks were formed [31]. 

Guy predicts permeability coefficients for sucrose and water that are factors of 150 and 3 times lower than the experimental values reported in Flynn s (1990) compilation. The fit between predicted and experimental permeability of the permeants with log values between -1 and 0 is more satisfactory. Glucose is the most polar compound included in the data reported by Acker-mann et al. (1987). The correlation resulting from the analysis of Potts and Guy for Ackermann s data set underestimates the permeability of glucose by a factor of 10. The magnitudes and direction of these discrepancies cause some doubt as to the adequacy of the proposed correlations in the polarity and MW range of sucrose and glucose. 

Figure 5.11 Relationship of permeability coefficients of neutral molecules (urea, glucose and saccharose) through the cation exchange membrane NEOSEPTA CM-1 and the same membrane with a polypyrrole layer to the Stokes radius of the solutes. ( ) Cation exchange membrane without the layer (NEOSEPTA CM-1) (O) membrane with a polypyrrole layer facing the dilute side in the measurement (A) membrane with polypyrrole layer facing the concentrated side. One surface of ferric ion form NEOSEPTA CM-1 was in contact with an aqueous pyrrole solution for 10 min to form a polypyrrole layer (polymerization time 10 min.).

Figure 7. Sugar permeability plot for bilayer lipid membrane (egg lecithin-cholesterol in n-decane) at 25 °C. The slope of the plot before and after addition of extract is equal to the permeability coefficient. Passive diffusion of D-[ C]glucose (O) and facilitated diffusion ( ) on addition of band 4.5 (sugar transporter) at a concentration of 0.99 (Jig cm to the trans side of the bilayer. (Reproduced with permission from Ref. 44. Copyright 1982 Elsevier Science.)...

In 1981, Helfrich [7] studied the effect of the external osmotic pressure on egg yolk phosphatidylcholine (EPC) giant vesicles by adding 15 mM of salt or glucose in the external medium of the vesicles. The vesicle radius appears to decrease linearly with time according to the law d /dt = -aPAc, where P is the membrane permeability coefficient to water, a, is the water molar volume, and Ac, the difference of molar concentrations. The water permeability coefficient for EPC bilayers was found to be 41 pms . ... 

Amphiphilic network tubules varying in composition and Me,hydrophilic were evaluated fiirther for permeability and diffusion coefficients for glucose, insulin and albumin (Table II). There was some variability in thickness of the membranes due to experimental conditions but this was factored into the calculations. 

As expected, glucose was freely permeable through the membranes while insulin was somewhat less permeable and albumin was impermeable. The membranes exhibited superior permeability characteristics. Membranes with higher Mc,hydrophiiic were more permeable to insulin. In comparison, the diffusion coefficients of glucose and insulin through membranes prepared with poly(hydroxyethyhnethacrylate) as the hydrophilic segment were only 0.042 and 0.009 X 10 (cm /sec) respectively (15). Earlier diffusion studies performed with different MA-PEB-MA membranes formed into flat membranes (15,18) gave very similar results as described herein for tubules. Our results for insulin permeability and diffusion indicate that the membranes and the tubules are satisfactory for use in an artificial pancreas biodevice. On the basis of these results the A-10-40 network was chosen for further in vitro and in vivo experiments. 

The Nation coating must protect the underlying sensor elements from compounds in the body, selectively transport O2 relative to glucose, and should preferably inhibit interfering species such as ascorbic acid (2,7J-7J). The permeability of Nation to several compounds was determined using a Nafion-coated rotating disk electrode (79). From plots of the inverse of the observed disk current as a fiuiction of the inverse of the square root of the rotation rate (a Koutecky-Levich plot) the permeability. Pm, was obtained. This value was determined for a series of Nation thicknesses, measured by ellipsometry, and the effective diffusion coefficients were obtained, according to equation 1. 

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