Enhanced membrane permeability to phenol red by medium-chain glycerides: studies on the membrane permeability and microviscosity.

To clarify the mechanism of the drug absorption enhancement by medium-chain glycerides (MCG), the changes in membrane permeability provoked by MCG were investigated with liposomal uptake experiments. Uptake of phenol red (PR) into liposomes increased with an increase in MCG content in the liposomal membrane, suggesting that PR absorption was enhanced in the "transcellular route." However, the apparent membranous microviscosity obtained in fluorescence depolarization studies tended to increase with the addition of MCG in both the hydrophobic core and the polar head regions of the liposomal membrane. Thus, an enhancement in membrane permeability caused by MCG was not accompanied by a decrease in the apparent membranous microviscosity.