Diffusion studies of bile acids, fatty acids and sucrose-NaCl-water systems at 37 °C by a modified capillary cell apparatus and their application to membrane transport studies

A capillary cell apparatus is described that allows accurate measurement of solute tracer diffusion coefficients in biological solutions at 37 °C. The apparatus has a unique stirring mechanism to provide a uniform flow pattern over the capillaries with only 18 ml of the bulk solution. Four capillaries of 2 cm length are used. With this apparatus measurement can be made at relatively short time periods so that bacterial overgrowth in the solutions is minimized. Using this apparatus tracer diffusion coefficients of three bile acids, cholic, taurochollic and taurodeoxycholic acids, and four fatty acids, acetic, pentanoic, octanoic and decanoic acids, were measured in an isotonic phosphate buffer, pH 7.1, at 37 °C. Viscosity, density and diffusion coefficients of sucrose in physiological saline solutions were also measured.