Calcein accumulation as a fluorometric functional assay of the multidrug transporter

Zsolt Holló, László Homolya, C. William Davis, Balázs Sarkadi

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Acetoxymethyl ester (AM) derivatives of various fluorescent indicators (fura-2, fluo-3, indo-1, BCECF, calcein) are actively extruded by the multidrug transporter (MDR1, P-glycoprotein - Homolya, L. et al. (1993) J. Biol. Chem. 268, 21493-21496). In the present paper we show that the measurement of the accumulation of a fluorescent cell viability marker, calcein, can be effectively used as a rapid and sensitive fluorometric and flow cytometric assay for studying P-glycoprotein function. The rate of calcein accumulation in human MDR1-expressing cells is significantly lower than in the control cells, while various drug-resistance reversing agents (verapamil, vinblastine, oligomycin, cyclosporin A and UIC2 monoclonal antibody) greatly increase calcein trapping only in the MDR1-expressing cells. Since calcein-AM is not fluorescent and free calcein is not a substrate of the multidrug transporter, the assay is readily applicable for rapid kinetic studies of the MDR1 function. Calcein has a high fluorescence intensity in the visible range, thus changes in calcein uptake can be easily visualised and MDR1-expressing and control cells separated by conventional flow cytometry.

Original languageEnglish
Pages (from-to)384-388
Number of pages5
JournalBBA - Biomembranes
Issue number2
Publication statusPublished - May 11 1994



  • Calcein
  • Flow cytometry
  • Fluorescent indicator
  • Fluorometry
  • Functional assay
  • MDR1
  • P-glycoprotein

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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