Analysis of the diffusion of bile salt/phospholipid micelles in rat intestinal mucin

The interaction of sodium taurocholate/egg phosphatidylcholine (TC/PC) mice lles with mucin was determined to investigate the exclusion of lipids by mu cus in the absorption process. The distribution of TC/PC was assessed at tw o intermicellar and three phospholipid concentrations with isolated, rat in testinal mucin (RIM) by dialysis. The diffusion coefficients were measured by NMR spectroscopy. At high [PC], RIM had lower [PC] relative to the contr ol, while the concentration of TC was largely independent of mucin concentr ation. The PC diffusion coefficients were reduced in the presence of RIM. T he magnetization decay of TC was compared with simulations to provide estim ates of the monomeric diffusivity and exchange rate constant. The rate cons tants increased with increasing micelle concentration, and the free TC diff usion coefficient was reduced in the presence of mucin. Mucin has an exclus ive effect on TC/PC mixed micelles that has been quantitatively determined through the use of diffusion measurements of dialyzed samples. (C) 2001 Els evier Science Ireland Ltd. All rights reserved.