Endocytosis of BSA-gold (5 nm gold) in cultured megakaryocytes. Immunolabeling as indicated on the figure. Compartments that have incorporated the tracer are shown. (A) Characteristic tubulo vesicular endosome close to the plasma membrane containing also GPIIb-IIIa. (B) Endosome with adjacent small vesicles containing the tracer (arrowhead). (C) Tubulo vesicular endosomes (asterisks) and a type I MVB (arrow). (D) MVB type II (asterisk) and two adjacent α-granules (α) both contain the endocytic tracer (arrowheads). Bars, 100 nm.