Abstract

[14C]amodiaquin accumulation by washed erythrocyte preparations was characterized to permit comparisons with chloroquine accumulation. Erythrocytes infected with Plasmodium berghei CS (chloroquine-susceptible) accumulate amodiaquin by a saturable process that has an apparent dissociation constant for amodiaquin of 7.6 X 10(-8) M and is competitively inhibited by chloroquine, quinine and quinacrine, as is the process of chloroquine accumulation. Within experimental error, the K1 of 8 X 10(-7) M estimated for chloroquine is the same regardless of whether the drug being accumulated is [14C]amodiaquin or [14C]chloroquine. Likewise, the K1 for amodiaquin is the same regardless of which drug is being accumulated. In addition, glucose stimulates and hydrogen ion, cold or interruption of glycolysis inhibits amodiaquin as well as chloroquine accumulation. These findings are evidence that a single process serves to accumulate both drugs. In the absence of substrate, erythrocytes infected with P. berghei CR (chloroquine-resistant) accumulate twice as much amodiaquin as chloroquine, and they accumulate more amodiaquin than do erythrocytes infected with P. berghei CS. These differences occur because P. berghei CR infects polychromatophilic erythrocytes possessing a high-affinity, substrate-independent process of accumulation to which amodiaquin has greater access than chloroquine. In the presence of glucose, amodiaquin accumulation by erythrocytes infected with P. berghei CR, when plotted as a function of amodiaquin concentration in the medium, describes a sigmoid curve.