Organic Cation Transporter 1 (OCT1/mOct1) is Localized in the Apical Membrane of Caco-2 Cell Monolayers and Enterocytes Number of text pages: 30 Number of tables: 0 Number of figures: 5 Number of references: 23 Number of words in the Abstract: 248 Number

Abstract Organic cation transporters (OCTs) are members of the solute carrier 22 (SLC22) family of transporter proteins that involved in absorption, distribution, and excretion of organic cations. While OCT3 is localized in the apical (AP) membrane of enterocytes, the literature is ambiguous about OCT1 (mOct1) localization, with some evidence suggesting basolateral (BL) localization in human and mouse enterocytes. This is contrary to our preliminary findings showing AP localization of OCT1 in Caco-2 cell monolayers, an established model of human intestinal epithelium. Therefore, this study aims at determining the localization of OCT1 (mOct1) in Caco-2 cells, and human and mouse enterocytes. Functional studies using OCT1-specific substrate pentamidine showed transporter-mediated AP but not BL uptake in Caco-2 cells, human and mouse intestinal tissues. OCT1 inhibition decreased AP uptake of pentamidine by ~50% in all three systems, with no effect on BL uptake. shRNA-mediated OCT1 knockdown in Caco-2 cells decreased AP uptake of pentamidine by ~50%, but did not alter BL uptake. Immunostaining and confocal microscopy in all three systems confirmed AP localization of OCT1 (mOct1). Our studies unequivocally show AP membrane localization of OCT