Plasma membranes collected from BeWo cells treated with HBSS, MβCD (5 mM, 1 h), or MβCD (5 mM, 1 h) and then MβCD-cholesterol (5 mM, 30 min) were subjected to density gradient ultracentrifugation in order to isolate detergent-resistant lipid rafts. Ten 1.4 mL fractions were collected and analyzed for protein or cholesterol content as described in the Materials and Methods. Data are presented as mean ± SE (n = 3 independent experiments).