Expression of P-glycoprotein, encoded by MDR 1 gene, a metabolically active efflux pump in murine mast cells

Mast cell line (MC/9) derived from normal murine liver was examined for the expression of P-glycoprotein (P-gp) at the level of protein with C-219 and JSB-1 monoclonal antibodies, using flow cytometry and Western blot, and at the level of mRNA by the reverse transcriptase-polymerase chain reaction. The function of P-gp was analyzed by the accumulation and efflux of rhodamine 123 (Rh123) in the presence or absence of cyclosporin A (CSA) and a non-immunosuppressive analog of CSA (CSA-1), P-gp both at the protein and mRNA levels was expressed in mast cells. Intracellular accumulation of Rh123, in the presence of CSA and CSA-1 was significantly greater than in their absence. Furthermore, both CSA and CSA-1 inhibited Rh123 efflux from mast cells. These data suggest the presence of a functionally active P-gp in mast cells. A possible physiologic role for P-gp in the secretion of certain mediators/cytokines from mast cells is suggested.