Quantitation of the in vitro free cholesterol exchange of human red cells and lipoproteins.

The exchange of free cholesterol in vitro between human red blood cells and low density lipoproteins (LDL) was quantified. The flux of sterol between LDL and red cells was relatively constant over a wide range of concentrations of free cholesterol in lipoproteins. In a system containing a suspension of red blood cells in a mixed solution of high density lipoproteins (HDL) and LDL, the fractional rate of exchange of HDL cholesterol was most rapid followed by LDL and lastly, by red cells. Increasing the ionic strength of the incubation media had no effect on the exchange of cholesterol between LDL and red cells. However, when both HDL and LDL were incubated with red cells in a buffer of increased ionic strength, total red cell cholesterol exchange was unaltered, but proportionately more exchange occurred with HDL and less with LDL. Addition of acetone to the buffer increased the exchange of cholesterol between LDL and red cells but produced no increment in red cell-HDL exchange.