MDR1 in taste buds of rat vallate papilla: functional, immunohistochemical, and biochemical evidence.

Multidrug resistance P-glycoprotein (MDR1) is a membrane protein of 150-170 kDa that catalyzes the ATP-driven efflux of hydrophobic xenobiotics, including fluorescent dyes, from cells. Expressed in many epithelial tissues and in the endothelia of the blood-brain barrier, the MDR1 protein provides major routes of detoxification. We found that taste cells of the rat vallate papilla (VP; posterior tongue) had only a slow increase in fluorescence due to uptake of the hydrophobic dye calcein acetoxymethyl ester. However, the development of fluorescence was accelerated two- to threefold by substrates and/or inhibitors of MDR1, such as verapamil, tamoxifen, and cyclosporin A, and by addition of the transport-blocking antibody to MDR1, UIC2. Western blots of vallate tissue rich in taste buds with the MDR1-specific monoclonal antibodies C219 and C494 revealed an immunoreactive protein at approximately 170 kDa. In contrast, the lingual epithelium surrounding the VP showed a much weaker band with these antibodies. Furthermore, using the antibodies C494 and UIC2 with tissue sections, MDR1-like immunoreactivity was found in taste cells. These results show that MDR1 is present and functional in vallate taste cells of the rat. MDR1-related transport may achieve active elimination of xenobiotics from the sensory cells and thereby protect the peripheral taste organs from potentially harmful molecules contained in an animal's food.