Fluid-phase pinocytosis mediates LDL uptake.

<p>(A) Wild-type macrophages were incubated 6 h with either 25 µg/ml ¹²⁵I-LDL alone, or 25 µg/ml ¹²⁵I-LDL and 500 µg/ml unlabeled LDL. CD36 KO macrophages (ΔCD36) and SRA KO macrophages (ΔSRA) macrophages were incubated 6 h with 25 µg/ml ¹²⁵I-LDL alone. (B) Wild-type macrophages were incubated 6 h with either 25 µg/ml ¹²⁵I-AcLDL alone, or 25 µg/ml ¹²⁵I-AcLDL and 500 µg/ml unlabeled AcLDL. CD36 KO macrophages (ΔCD36) and SRA KO macrophages (ΔSRA) macrophages were incubated 6 h with 25 µg/ml ¹²⁵I-AcLDL alone. Incubations were performed in serum-free medium containing 50 ng/ml M-CSF. Uptake values represent the sum of cell-associated and degraded ¹²⁵I-labeled lipoprotein. The range of cell-associated and degraded ¹²⁵I-LDL was 17–21% and 79–83%, respectively. The range of cell-associated and degraded ¹²⁵I-AcLDL was 16–18% and 82–84%, respectively. ¹²⁵I-LDL uptake was not competed with excess unlabeled LDL consistent with fluid-phase pinocytosis mediating uptake. Statistical tests compare each treatment group with wild-type macrophages incubated with 25 µg/ml ¹²⁵I-AcLDL. * = <i>p</i><0.05. ** = <i>p</i><0.01. *** = <i>p</i><0.001. There was no statistical difference between macrophage groups incubated with ¹²⁵I-LDL.