Cell-surface shedding by fibroblasts in culture

The metabolic fate of cell-surface components was studied by labeling the surface of cultured chick embryo cells with [14C]glucosamine for 24 h, or by lactoperoxidase-catalyzed radioiodination. The cells were then cultured further in label-free medium for 24 h. At different time intervals thereafter, cells and culture medium were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The radioactivity profile of the metabolically labeled material in the medium was similar to that of the [125I]lactoperoxidase-labeled cells. The rate of disappearance of labeled macromolecular components from the cell surface was a mirror image of the rate of accumulation of these components in the medium. Analysis on 7 to 20% acrylamide gradient slab gel revealed that most of the labeled macromolecules in the medium comigrate with the surface micromolecules obtained from intact cells. It thus appears that at least some cell-surface components are shed in undegraded form. The possible biomedical implications of the detection of intact cellular membrane components in the circulation are discussed.