FUNCTIONAL EXPRESSION OF P-GLYCOPROTEIN IN AN IMMORTALIZED CELL-LINE OF RAT-BRAIN ENDOTHELIAL-CELLS, RBE4

The presence of P-glycoprotein in the cell plasma membrane limits the penetration of many cytotoxic substances into cells that express the g ene product. There is considerable evidence also to indicate that P-gl ycoprotein is expressed as part of the normal blood-brain barrier in t he luminal membranes of the cerebral capillary endothelial cells, wher e it presumably performs a protective function for the brain. This rep ort describes the functional expression of P-glycoprotein in an immort alised cell line, RBE4, derived from rat cerebral capillary endothelia l cells. The expression of P-glycoprotein is demonstrated by western i mmunoblotting and by immunogold and fluorescent staining with monoclon al antibodies. The cellular accumulation of [H-3]colchicine and [H-3]v inblastine is investigated and shown to be enhanced by the presence of azidothymidine, chlorpromazine, verapamil, cyclosporin A, and PSC 833 ([3'-keto-Bmt(1)][Val(2)]-cyclosporin) at 50 or 100 mu M concentratio n. It is concluded that the RBE4 cell line is a valuable tool for inve stigating the mechanisms of P-glycoprotein activity both in the blood- brain barrier and in multidrug resistance in general.