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

The interaction of sodium taurocholate/egg phosphatidylcholine (TC/PC) micelles with mucin was determined to investigate the exclusion of lipids by mucus in the absorption process. The distribution of TC/PC was assessed at two intermicellar and three phospholipid concentrations with isolated, rat intestinal mucin (RIM) by dialysis. The diffusion coefficients were measured by NMR spectroscopy. At high [PC], RIM had lower [PC] relative to the control, while the concentration of TC was largely independent of mucin concentration. The PC diffusion coefficients were reduced in the presence of RIM. The magnetization decay of TC was compared with simulations to provide estimates of the monomeric diffusivity and exchange rate constant. The rate constants increased with increasing micelle concentration, and the free TC diffusion coefficient was reduced in the presence of mucin. Mucin has an exclusive effect on TC/PC mixed micelles that has been quantitatively determined through the use of diffusion measurements of dialyzed samples.