Expression of functionally P-glycoprotein in MA104 kidney cells

Rhesus monkey kidney MA104 cells are a polarized epithelium with some unusu al characteristics, including a resistance to ouabain, although their Na+-K +-ATPase has normal affinity with this drug. This work suggests that MA104 cells have high expression of functionally P-glycoprotein in their membrane s. This was established using four complementary methods to investigate the expression and function of P-glycoprotein in these cells. MA104 cells were strongly resistant to vincristine, which could be reversed by three known P-glycoprotein modulators: verapamil, cyclosporin A and trifluoperazine. In addition, MA104 cells accumulate little rhodamine 123, and the incubation with verapamil increased this accumulation. The mdr1-mRNA was detected by r everse transcription-polymerase chain reaction and a subcloned 283-bp produ ct was identified. Its nucleotide sequence was compared with the related re gion of human mdr1, showing a high identity (96%) between the two sequences . The expression of P-glycoprotein in the cell membrane was observed by Wes tern blot and immunofluorescence. The results taken together suggest that M A104 cells intrinsically have a high expression of functionally P-glycoprot ein in their membranes.