Intracellular pH does not affect drug extrusion by P-glycoprotein.
The intracellular pH (pH(i)) of cells exhibiting multidrug resistance (MDR) related to the expression of the P-glycoprotein (Pgp) is often more alkaline than that of the parental cells, as also observed for the KB-V1/KB-3-1 system in this paper. The possible role of an elevated pH(i) in Pgp-related MDR has been investigated by shifting back the pH(i) of the MDR+ cells to a more acidic value using the mobile proton ionophore carbonylcyanide m-chlorophenylhydrazone (CCCP). The influence of CCCP-evoked delta pH(i) on relative daunorubicin (DNR) accumulation was similar in the case of several Pgp positive and negative cell lines, in view of flow cytometric and radioactive drug accumulation studies and measuring DNR levels in the medium in a flow-through system. Our data argue against a significant effect of pH(i) on Pgp pumping efficiency. However, an indirect connection between pH(i) regulation and the MDR phenotype is suggested by the fact that acidification of the external medium in the presence of verpamil could be observed exclusively in MDR+ cells.
Goda
K
K
Department of Biophysics, University Medical School of Debrecen, Hungary.
Balkay
L
L
Márián
T
T
Trón
L
L
Aszalós
A
A
Szabó
G
G
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D003630:Daunorubicin / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D007476:Ionophores; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D003630:Daunorubicin