Uptake of 7-dehydro derivatives of cholesterol, campesterol, and beta-sitosterol by rat erythrocytes, jejunal villus cells, and brush border membranes.

We have determined the effect of the side chain on the uptake of sterols from micellar solutions by isolated rat jejunal villus cells, brush border membranes, and erythrocytes. From an equimolar mixture of 7-dehydrosterols, the uptake decreased with an increasing number of carbon atoms at C24 of the sterol side chain in a manner identical to that observed for the parent-delta 5-sterols. The brush border and erythrocyte membranes were found to absorb 4-5 times more 7-dehydrocholesterol than 7-dehydro-beta-sitosterol over a 60-min period of incubation. A somewhat lower specificity of sterol uptake by the villus cells was attributed to the exposure of large areas of the basolateral membrane, which apparently was less able to discriminate between sterols. The higher sterol selectivity was associated with higher membrane organization anticipated from the higher free cholesterol/phospholipid and protein/phospholipid ratios of the brush border and red blood cell membrane. On a mass basis the villus cells and brush borders absorbed 30-60 times more sterol than the erythrocytes. Assuming that the delta 5,7-sterols accurately represent the absorption of the delta 5 parent sterols, it is suggested that the 3- to 5-fold excess of absorbed cholesterol over beta-sitosterol that is typically found in the jejunal wall of the rat following feeding of radioactive sterols arises from an inability of beta-sitosterol to enter the brush border membrane as easily as cholesterol.