AJP - Gastrointestinal and Liver Physiology, Vol 252, Issue 3 309-G314, Copyright © 1987 by American Physiological Society
Distribution and monomer activity of cholesterol in micellar bile salt: effect of cholesterol level
K. Chijiiwa and W. G. Linscheer
Despite the fact that uptake of cholesterol by the enterocyte occurs as a
monomer from the intermicellar aqueous phase in equilibrium with micelle,
the cholesterol monomer concentration in the aqueous phase and the
partition coefficient between intermicellar aqueous phase and micellar
aggregate have not been clarified. The present study deals with the
distribution of cholesterol and monomer activity in constant bile
salt-fatty acid micellar solutions with different cholesterol
concentrations. In addition, uptake of cholesterol from these micellar
solutions into rat jejunum was studied using everted sacs. Cholesterol
monomer concentration in the aqueous phase increased linearly with the
concentration of cholesterol in the micellar solution. Partition
coefficient of cholesterol between the aqueous phase surrounding micelle
and micellar aggregate was essentially constant at any cholesterol level (K
= 3 X 10(-2)). Cholesterol monomer activities were linearly proportional to
the cholesterol concentrations in the micellar solutions and correlated
well with the rate of cholesterol uptake. It is concluded from these
experiments that a partitioning phenomenon determines cholesterol monomer
concentrations in the intermicellar aqueous phase from which the
cholesterol is absorbed. After disappearance of the cholesterol monomers
from the aqueous phase, these monomers are replaced by a shift of monomers
from the intramicelle to intermicellar aqueous phase, under constant
partition coefficient between extra- and intramicelle. The bile salt
micelle provides a huge reservoir for partitioning of cholesterol monomers.
