TABLE 1.

Resting vacuolar Ca²⁺ concentration of P. falciparum strains with various chloroquine sensitivities

Strain^a	CQ 50% inhibitory concn (nM)^b	Verapamil effect^c	Resting vacuolar [Ca²⁺] (μM)^b
TM6	93 ± 7	Yes	1.68 ± 0.97
3D7	8 ± 2	No	2.34 ± 0.35
C3^Dd2	50 ± 3	Yes	1.84 ± 0.71
C2^GCO3	10 ± 3	No	1.93 ± 0.28
D10^D10	23 ± 2	No	1.95 ± 0.10
D10^7G8	16 ± 2	No	2.12 ± 0.60

TM6 is a laboratory-adapted CQ-resistant strain; 3D7 is a laboratory-adapted CQ-sensitive strain. In clone C3^dd2, the pfcrt allele of a CQ-sensitive clone (GCO3) has been replaced by the pfcrt allele of the CQ-resistant clone Dd2 (14). In clone C2^GCO3, the sensitive pfcrt allele from a CQ-sensitive clone has been replaced by another CQ-sensitive pfcrt allele (14) (as a control for any basal effect of pfcrt allelic exchange). In clone D10^D10, the pfmdr allele from a CQ-sensitive isolate (D10) was replaced by the pfmdr allele from the same CQ-sensitive clone (11). In clone D10^7G8, the pfmdr allele from a CQ-sensitive clone (D10) was replaced with a pfmdr allele from a CQ-resistant clone (7G8) (11).

Values represent means ± standard error from at least three independent measurements.

Ability of verapamil (5 μM) to chemosensitize the parasite clone to CQ (8).