ROLE FOR THE PLASMODIUM-FALCIPARUM DIGESTIVE VACUOLE IN CHLOROQUINE RESISTANCE

We have developed a method for the isolation of pure and intact Plasmo dium falciparum digestive vacuoles capable of ATP dependent chloroquin e (Ca) accumulation in vitro. The method is rapid and reliable, and it produces a high yield of vacuoles (20%). Ca accumulation in isolated vacuoles was found to be ATP-, Mg2+, and temperature dependent. We the n investigated the Ca-accumulating capabilities of vacuoles isolated f rom CQ-resistant (CQR) and CQ-sensitive (CQS) parasites. At external C a concentrations of 100 and 250 nM, vacuoles isolated from two CQS str ains (D10 and RSA3) (V-max: 380-424 fmol/10(6) vacuoles/hr) accumulate d significantly more CQ (similar to 3 times) than those isolated from three (FAC8, RSA11, and RSA15) of the four CQ-resistant strains of P. falciparum tested (V-max: 127-156 fmol/10(6) vacuoles/hr) (P less than or equal to 0.05). We propose that the low level of CQ accumulation o bserved in vacuoles isolated from most of the Ca-resistant parasites t ested contributes to the decreased CQ accumulation seen in these strai ns and, hence, to Ca resistance. Although it is often suggested that t he digestive vacuole of the P. falciparum parasite is involved in the mechanism of Ca resistance, to our knowledge this is the first direct confirmation. BIOCHEM PHARMACOL 56;3: 313-320, 1998. (C) 1998 Elsevier Science Inc.