Function of P-Glycoprotein

P-glycoprotein is not only expressed in tumor cells, but also in cells of several healthy tissues. In liver it was detected in the biliary canalicular surface of hepato-cytes and the apical surface of small biliary ductules. In the small intestine and colon, it is localized in the apical surface of columnar epithelial cells, and in kidneys it is found in the brush border membrane of proximal tubules. Moreover, it is detectable on the apical surface of small ductules in the pancreas and on the surface of cells in the medulla and cortex of adrenals [2]. 

The tissue distribution of P-glycoprotein yields important clues to its function. In most tissues it is localized to the apical (luminal) membrane of polarized epithelial cell layers. This location suggests that P-glycoprotein extrudes its substrates from the epithelial cells into the adjacent lumen. It is anticipated that P-glycopro-tein plays an important role as a protective mechanism against naturally occur- 

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