Uptake and transport of sterols by isolated villus cells of rat jejunum.

Abstract

Cellular uptake and transport of cholesterol and beta-sitosterol was studied in rat jejunal villus cells isolated by hyaluronidase dispersion. Sterol absorption was measured from micellar solutions using a Millipore filtration technique. In actively metabolizing cells both cholesterol and beta-sitosterol exhibited rapid initial uptake curves which leveled off after 10 min, corresponding approximately to a 1:1 sterol:phospholipid molar ratio within the microsomal membranes of the cell, which suggested a physicochemical end point. Using various proportions of cholesterol and beta-sitosterol in the incubation medium, it was shown that each sterol interfered with the absorption of the other, the one present in the highest concentration showing the relatively higher uptake. Mixtures of equimolar proportions were taken up by the cells in a ratio that slightly favoured beta-sitosterol, but significantly more cholesterol than beta-sitosterol was found to be transferred to the microsomes. The limited mass discrimination between cholesterol and beta-sitosterol seen in the isolated cells is in contrast to the preferential absorption of cholesterol in vivo. These studies demonstrate that the molecular basis for the differential transport of cholesterol and beta-sitosterol in the lymph observed in vivo must be sought at a higher level of physiological activity of the cells (e.g., chylomicron formation and secretion) than that achieved in the present experiments.