Figure 5

Quantification of membrane estrogen receptor (mER) and total estrogen receptor (tER) in mER-α-enriched (mER^high) and mER-α-depleted (mER^low) MCF-7 cells. (a) Different numbers of cells were fixed in the same manner as described in Fig. 1 and the level of mER was assessed with 8 μg/ml C-542 antibody. Closed and open circles represent mER^high and mER^low cells, respectively. The data were approximated with an exponential decay curve and compared by evaluating the difference between the sums of squares of the residuals from each curve with the sum of squares of the residuals for the combined curve using the F-test. The curves are significantly different (P = 0.0003). The diamond represents MDA-MB-231 cells and the cross-hatched horizontal bar the level of binding of a mouse IgG_1k isotype control antibody. (b) Level of total ER (intracellular estrogen receptor [iER] plus mER) for mER^high (closed circles) and mER^low (open circles) under the same binding conditions except for permeabilization of the cells. Where error bars for standard error are not visible, they are smaller than the size of the symbols. CV, crystal violet; pNp, paranitrophenol.