Figure 5. Inhibition of the substrate stimulated ATPase activity of Pgp and ABCG2 by retinol and 13-cis-retinoic acid.

The ATPase activity of Pgp (a,b) and ABCG2 (c,d) was stimulated by 40 μM verapamil and 10 μM quercetin, respectively. Representative data are shown out of three independent experiments performed in triplicate (data points are means ± SD). The curves were obtained by fitting the data points with a modified form of the Michaelis-Menten equation (see Materials and Methods, (R² ≥ 0.98)).