Fig. 3.

Relationship between ATP depletion and Pgp expression levels in various cells. In addition to the cell lines presented in Fig. 2 this study included canine MRP1-transfected cells, MDCKII-MRP1; human umbilical vein endothelial cells, HUVEC; bovine brain microvessel endothelial cells, BBMEC; and murine myoblast cells, C2C12. Identification of the drug efflux transport proteins was done using the immunoblot technique [18]. The levels of Pgp expression were quantified by densitometry and normalized to constitutively expressed β-actin. EC₅₀ values for ATP depletion following 2 h exposure of the cells to P85 were determined as discussed above. Vertical arrow separates cells with relatively high and low Pgp expression levels.