This study is concerned with a further development of the kinetics of the uptake in vitro of [4-14C] cholesterol by intima-media layers of thoracic aortas from normal rabbits. 1. 1. Separation of the intima-media [14C]cholesterol into the free nd esterified forms revealed that the majority of the labelled serum cholesterol, bound initially at the luminal endothelial cell membrane, was in the esterified form. Following the initial binding phase, no significant increase was observed in esterified [14C]cholesterol of the intima-media, whereas the intima-media content of free [14C]cholesterol increased with time at a rate equal to that for the uptake of total [14C]cholesterol in the second phase. A transport of esterified [14C]cholesterol across the endothelial cell surface would thus imply a hydrolysis following uptake. 2. 2. These findings are in agreement with the demonstration that less than 3% of the non-labelled intima-media cholesterol pool of the rabbits is found in the esterified form. 3. 3. Based on the above findings a model is shown for the uptake of cholesterol by intima-media. The mathematical treatment of the model indicates that the previously found relationship between cholesterol transfer rate and concentration of total cholesterol in serum is in agreement with the model. An estimation of the amount of cholesterol, which maximally can be bound per unit surface area, shows this amount to be of the same order of magnitude as the amount of cholesterol found in a lipoid monolayer of the same area. The rate constant for the cholesterol transfer across the endothelial cell surface is about the same order of magnitude as that for the ingestion in rabbit macrophages. 4. 4. The kinetics presented are compatible with morphological descriptions of a pinocytotic uptake process. © 1969.
