Relationships between rhodamine 123 transport, cell volume, and ion- channel function of P-glycoprotein

Guillermo A. Altenberg, Carlos G. Vanoye, Ernest S. Han, Joachim W. Deitmer, Luis Reuss*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

61 Scopus citations


The P-glycoprotein (Pgp), a plasma membrane protein overexpressed in multidrug-resistant tumor cells, is thought to be both an ATPase that actively exports cytotoxic drugs and a Cl- channel activated by cell swelling. The partial reversal of multidrug resistance by Cl- transport blockers suggests a possible role for Cl- in Pgp-mediated drug transport. We used multidrug-resistant Chinese hamster fibroblasts and human breast cancer cells expressing Pgp to study the roles of Cl- (and also Na+ and HCO3/- /CO2) on Pgp-mediated efflux of the fluorescent dye rhodamine 123 (R123). In Pgp-expressing Chinese hamster fibroblasts, exposed to isosmotic solutions, the unidirectional efflux of R123 was not measurably changed by a ~60-min removal of Cl- (or by exposure to Na+-free, or nominally HCO3/-/CO2- free medium); short term (2-3 min) ion substitutions were also ineffective. In human breast cancer cells transfected with human mdr1 cDNA, hyposmotic solutions activated a Cl- current but had no effect on the Pgp-mediated unidirectional efflux of R123. Additionally, in human breast cancer cells, the intracellular presence of R123 did not prevent activation of the Cl- current by hyposmotic solution. The lack of detectable effect of removal of Cl-, Na+, or HCO3/- on Pgp-mediated R123 transport rules out direct coupling between substrate transport and transport of either of these ions by Pgp. The persistence of Pgp-mediated R123 efflux in osmotically swollen cells indicates that activation of the Pgp-associated Cl- current does not hinder the Pgp pump function. The lack of effect of R123 on swelling-activated Cl- current denotes that Pgp-mediated transport of organic substrates and Pgp- associated Cl- currents can occur at the same time in a single cell. These results underscore the dissociation between Pgp-mediated active drug transport and electrodiffusive Cl- transport.

Original languageEnglish (US)
Pages (from-to)7145-7149
Number of pages5
JournalJournal of Biological Chemistry
Issue number10
StatePublished - 1994

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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