title: Chloroquine uptake, altered partitioning and the basis of drug resistance: evidence for chloride-dependent ionic regulation.
abstract: The biochemical mechanism of chloroquine resistance in Plasmodium falciparum remains unknown. We postulated that chloroquine-resistant strains could alter ion fluxes that then indirectly control drug accumulation within the parasite by affecting pH and/or membrane potential ('altered partitioning mechanism'). Two principal intracellular pH-regulating systems in many cell types are the amiloride-sensitive Na+/H+ exchanger (NHE), and the sodium-independent, stilbene-sensitive Cl-/HCO3- antiporter (AE). We report that under physiological conditions (balanced CO2 and HCO3-) chloroquine uptake and susceptibility are not altered by amiloride analogues. We also do not detect a significant difference in NHE activity between chloroquine-sensitive and chloroquine-resistant strains via single cell photometry methods. AE activity is dependent on the intracellular and extracellular concentrations of Cl- and HCO3- ions. Chloroquine-resistant strains differentially respond to experimental modifications in chloride-dependent homeostasis, including growth, cytoplasmic pH and pH regulation. Chloroquine susceptibility is altered by stilbene DIDS only on chloroquine-resistant strains. Our results suggest that a Cl(-)-dependent system (perhaps AE) has a significant effect on the uptake of chloroquine by the infected erythrocyte, and that alterations of this biophysical parameter may be part of the mechanism of chloroquine resistance in P. falciparum.
authors.affiliation: Kenneth S. Warren Laboratories, Tarrytown, NY 10591, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Martiney
authors.forename: A S
authors.initials: AS
authors.lastname: Ferrer
authors.forename: A
authors.initials: A
authors.lastname: Cerami
authors.forename: S
authors.initials: S
authors.lastname: Dzekunov
authors.forename: P
authors.initials: P
authors.lastname: Roepe
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000962:Antimalarials / Q000493:pharmacokinetics* / Q000627:therapeutic use; D002712:Chlorides / Q000378:metabolism*; D002738:Chloroquine / Q000493:pharmacokinetics*; D004232:Diuretics / Q000494:pharmacology; D004351:Drug Resistance; D010963:Plasmodium falciparum / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
chemical_list: D000962:Antimalarials; D002712:Chlorides; D004232:Diuretics; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D002738:Chloroquine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid