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 fo r the expression of P-glycoprotein (P-gp) at the level of protein with C-219 and JSB-1 monoclonal antibodies, using flow cytometry and Weste rn blot, and at the level of mRNA by the reverse transcriptase-polymer ase chain reaction. The function of P-gp was analyzed by the accumulat ion 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 CS A 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/cytoki nes from mast cells is suggested.