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Science 21 December 1973:
Vol. 182. no. 4118, pp. 1258 - 1261
DOI: 10.1126/science.182.4118.1258
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Articles

Diffusion of Weak Acids across Lipid Bilayer Membranes: Effects of Chemical Reactions in the Unstirred Layers

John Gutknecht 1 and D. C. Tosteson 1

1 Department of Physiology and Pharmacology, Duke University Medical Center, Durham, North Carolina 27710

Chemical reactions in the aqueous unstirred layers of solution adjacent to a membrane can have dramatic effects on the diffusion of solutes across that membrane. This is demonstrated by the diffusion of labeled salicylate and salicylic acid across a phospholipid bilayer membrane. Two types of chemical reactions are considered. The first is an isotopic exchange reaction between the ionic and nonionic forms of a weak acid, HA + *A- [unknown] H*A + A-. This reaction provides a way of estimating the true membrane permeability to a highly permeant weak acid and also a way of estimating the thickness of the unstirred layers. The second chemical reaction, the dissociation of a weak acid, HA [unknown] H+ + A-, can be used to show how the presence or absence of buffers in the unstirred layers controls the net transport of permeant weak acids across a membrane. In principle, the addition of appropriate "antacid" buffers to salicylates can increase their rate of absorption from the stomach.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)