Some Aspects of Fatty Acid Absorption and Metabolism by Isolated Epithelial Cells from Small Intestine

Haag, G.; Bierbach, H; Holldorf, August W.

doi:10.1007/978-94-011-7176-2_20

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“…Lamers and Hulsmann (1975) made similar calculations for octanoic acid in isolated intestinal cells. Nonmetabolic domination of long-chain fatty acid uptake was clearly demonstrated in isolated intestinal cells in which the rate of palmitate accumulation during 5-rain incubations was not affected by metabolic inhibitors or even by killing the cells (Haag, Bierbach & Holldorf, 1976). Although the exact sites of cellular accumulation are not known, it seems clear that nonmetabolic binding, not transmembrane diffusion, dominates the uptake of most medium-and long-chain fatty acids, especially at millimolar concentrations which are much higher than the Km's for metabolic product formation (DeGrella & Light, 1980a, b).…”

Section: Equilibration Rates In Cells and Tissuesmentioning

confidence: 95%

Monocarboxylic acid permeation through lipid bilayer membranes

1984

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The membrane permeability coefficients for the homologous monocarboxylic acids, formic through hexanoic, as well as benzoic and salicylic, were determined for egg phosphatidylcholine-decane planar bilayer membranes. The permeabilities of formic, acetic and propionic acid were also determined for "solvent-free" phosphatidylethanolamine bilayers. Permeability coefficients were calculated from tracer fluxes measured under otherwise symmetrical conditions, and precautions were taken to ensure that the values were not underestimated due to unstirred layer effects. The relation between the nonionic (HA) permeability (Pm) and the hexadecane/water partition coefficient (Kp) was: log Pm = 0.90 log Kp + 0.87 (correlation coefficient = 0.996). Formic acid was excluded from the analysis because its permeability was sixfold higher than predicted by the other acids. The permeabilities for "solvent-free" membranes were similar to those for decane-containing membranes. The exceptionally high permeability of formic acid and the high correlation of the other permeabilities to the hexadecane/water partition coefficient is a pattern that conforms with other nonelectrolyte permeabilities through bilayers. Similarly, the mean incremental free energy change per methylene group (delta delta G/-CH2-) was -764 cal mol-1, similar to other homologous solutes in other membrane systems. However, much less negative delta delta G values (-120 to -400 cal mol-1) were previously reported for fatty acids permeating bilayers and biological membranes. These values are due primarily to unstirred layer effects, metabolism and binding to membranes and other cell components.

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Section: Equilibration Rates In Cells and Tissuesmentioning

confidence: 95%