Electron micrographs of the effect of inhibitors of uptake on type II collagen (CII) internalization by macrophages. Macrophages were pulsed with 200 μg/ml CII for 30 minutes in the presence of (a) 10.0 μM cytochalasin D, (b) 1.0 mM amiloride, (c) 5.0 μM monodansylcadaverine (MDC) or (d) 0.4 μg/ml filipin and analyzed by electron microscopy. Magnification: (a) ×6,610; (b) ×52,000; (c) ×21,000; (d) ×73,000. Bar = (a,c) 1 μm or (b,d) 200 nm. Black arrows show fibrils of collagen aligned parallel to the plane of the section; the white arrow shows an unwinding collagen fibril inside the cell. Sections through several planes of more than 50 cells were examined for each treatment.