AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 4 671-G675, Copyright © 1990 by American Physiological Society
Acidic mucin layer facilitates micelle dissociation and fatty acid diffusion
Y. F. Shiau, R. J. Kelemen and M. A. Reed
Department of Medicine, University of Pennsylvania, Philadelphia.
The presence of a mucin layer on the surface of the intestinal epithelium
has been suggested as an important factor in maintaining an acidic
microclimate. The presence of such a low-pH compartment has been shown to
facilitate fatty acid uptake. The mechanisms leading to the enhancement of
fatty acid uptake were investigated in a purified acidic mucin layer. Our
results indicate that the presence of a low-pH compartment indeed
facilitates the dissociation of mixed micelles made of taurocholate and
oleic acid. The released fatty acid formed an emulsion at the mucin layer,
and this event could be visualized by the naked eye. When the size of the
particles in the micelle solution was examined by photon correlation
spectroscopy, it was found that acidification alone can lead to the
formation of particles with size substantially greater than that of
micelles. With the use of labeled fatty acid, the change in optical density
can be correlated to the amount of fatty acid appearing in the mucin layer
in an asymptotic fashion, suggesting that using the turbidity as an
indicator might underestimate fatty acid diffusion. Despite this
limitation, the rate of fatty acid diffusion in the mucin layer was
estimated to be 400% of that in the buffer solution.
