Pharmaceutical Research

, Volume 20, Issue 8, pp 1192–1199

Rhodamine 123 Requires Carrier-Mediated Influx for Its Activity as a P-Glycoprotein Substrate in Caco-2 Cells


DOI: 10.1023/A:1025096930604

Cite this article as:
Troutman, M.D. & Thakker, D.R. Pharm Res (2003) 20: 1192. doi:10.1023/A:1025096930604


Purpose. The purpose of this work was to elucidate transport pathways of the P-glycoprotein (P-gp) substrates rhodamine 123 (R123) and doxorubicin across Caco-2 cells.

Methods. Experiments were designed to identify saturable and nonsaturable transport processes and transport barriers for R123 and doxorubicin transport across Caco-2 cells. Confocal laser scanning microscopy (CLSM) imaged R123 transport under normal conditions and in the presence of the P-gp inhibitor, GW918 (used to abolish P-gp-mediated efflux activity).

Results. R123 secretory Papp (Papp,BA) showed concentration dependence, whereas R123 absorptive Papp (Papp,AB) did not. Inhibition of P-gp efflux revealed that P-gp-mediated efflux had no effect on R123 or doxorubicin Papp,AB, but enhanced R123 and doxorubicin Papp,BA. In calcium-free medium, R123 Papp,AB increased 15-fold, indicating intercellular junctions are a barrier to R123 absorption. CLSM of R123 fluorescence during absorptive transport under normal conditions and in the presence of GW918 was identical, and was limited to paracellular space, confirming that P-gp is not a barrier to R123 absorption. CLSM revealed that R123 fluorescence during secretory transport under normal conditions and in the presence of GW918 was localized intracellularly and in paracellular space. R123 and doxorubicin uptake across Caco-2 cells basolateral membrane was saturable.

Conclusions. R123 absorptive transport occurs primarily by paracellular route, whereas R123 secretory transport involves influx across BL membrane mediated solely by a saturable process followed by apically directed efflux via P-gp. Doxorubicin utilizes similar transport pathways to cross Caco-2 cells.

P-glycoproteinrhodamine 123doxorubicinintestinal absorptionintestinal secretion

Copyright information

© Plenum Publishing Corporation 2003

Authors and Affiliations

  1. 1.Division of Drug Delivery and Disposition, School of Pharmacythe University of North Carolina at Chapel HillChapel Hill