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.