Effects of DIDS and BSP on apo A-I–mediated cholesterol efflux. Cholesterol-loaded and [³H]cholesterol–labeled normal fibroblasts were incubated for 6 hours with or without 5 μg/mL apo A-I and the indicated concentrations of DIDS or BSP. [³H]cholesterol efflux was measured as the percentage of total radiolabeled cholesterol appearing in the medium (y axis). Results are the mean ± SD (n = 3) of efflux in the presence of apo A-I after subtraction of values for apo A-I–free medium.