Transport behavior of four bile salt micelles and cholesterol solubilized by their micelles across porous membrane

The transport behavior of bile salts (BSs) solubilizing cholesterol (Ch) or none across an artificial membrane was investigated for sodium salts of deoxycholic acid (NaDC), chenodeoxycholic acid (NaCDC), ursodeoxycholic acid (NaUDC) and cholic acid (NaC) in tetraborate-carbonate buffer solution at pH 10.0 and 37 degrees C. The study demonstrated that the surfactant properties such as critical micellization concentration (CMC) and micellar size or diffusion coefficient were determinable from the flux or permeability measurements. The comparison among the respective pure systems of BSs led to a conclusion that the micellar size was in the order of NaDC > NaCDC > NaUDC > NaC and determined CMC values were in agreement with those in literature. The magnitude of solubilizing power (capacity) of BS for Ch was found to decrease in the order of NaDC > NaCDC > NaC > NaUDC; this order is in accordance with that of the empirical hydrophobicity index. The hydrodynamic radii for the singly dispersed species and the micellar species of the respective BSs and of Ch-solubilizing micelles were estimated from the permeability data; the radii of the Ch-solubilizing micelles are approximately 12-15 Angstrom and interestingly, smaller than those of the respective BS alone micelles ranging from 14 to 22 Angstrom.