Figure 5.

Kinetics of fluorescently labeled Tfn uptake into human melanoma cells. The cells were grown on glass coverslips and were either untreated (circles), or subjected to cholesterol depletion by treatment with mβCD (rectangles), or cholesterol enriched by exposure to cholesterol complexed with mβCD (triangles). Cholesterol levels were determined as described in Materials and Methods. (A) Raw data. Experimental data are indicated by the symbols. Solid lines are the fit to Eq. 4 using rate constants k₋₁ + k₂ obtained from the SPR measurements. (B) Normalized data, I_fluo(t)/I_fluo(t = 20 min). The inset shows dependence of rate constants on cholesterol level in the plasma membrane. The lines connect between the symbols. The inset describes the dependence of rate constants on cellular cholesterol levels.