The strongest expression of P-glycoprotein is in the blood-brain barrier

P-glycoprotein (P-gp), an active efflux pump of antitumor drugs, is strongly expressed in endothelial cells of the blood brain barrier (BBB). Two proteins (155 and 190 kDa) were detected by Western blot analysis of beef and rat capillaries with the monoclonal antibody (MAb) C219. In order to characterize the nature of these proteins, biochemical studies were performed in comparison with P-gp from the CH(R)C5 tumoral cell line. Results suggest that only p155 is the P-gp in BBB and that MAb C219 cross-reacts with a 190 kDa MDR-unrelated glycosylated protein. Western blot analysis shows presence of P-gp in several tissues and presence of p190 in some tissues. P-glycoprotein was predominantly expressed in brain capillaries compared to other tissues.