Binding of plasma fibronectin to the surfaces of BHK cells in suspension at 4 °C

Plasma fibronectin is shown by several different criteria to bind to suspended BHK cells if the binding incubations are carried out at 4 °C. In indirect immunofluorescence experiments, fibronectin bound to suspended BHK cells at 4 °C in a punctate distribution over the entire cell surfaces. Little binding, however, was detected on cells incubated with fibronectin at 37 °C. The fibronectin bound to the cells at 4 °C was functionally active, since these cells subsequently were able to spread on tissue culture dishes in protein-free medium, unlike cells preincubated with fibronectin at 37 °C or in the absence of fibronectin. Also, the cell surface receptors for soluble fibronectin and fibronectin-coated beads appeared to be similar, since cells preincubated with fibronectin at 4 °C subsequently bound fewer fibronectin-coated beads than control cells. In biochemical studies with radiolabeled fibronectin, binding of fibronectin to the cells was shown to increase with incubation time up to 4 h. In competition experiments with unlabeled fibronectin, 30% of the binding of radiolabeled fibronectin could be inhibited.