Membrane potential of Plasmodium falciparum gametocytes monitored with rhodamine 123

The membrane potential of Plasmodium falciparum gametocytes was monitored with the cationic permeant fluorescent dye rhodamine 123 (R123) as a probe. Epifluorescence microscopy revealed that R123 at 1 microgram/ml rather selectively partitioned into structure resembling large mitochondria. Treatment of R123-loaded gametocytes with various inhibitors including those of respiration resulted in disappearance of fluorescence from what appeared to be the mitochondria, but not from the cytosol. These results indicate that P. falciparum gametocytes have the mitochondrion maintaining an inside negative membrane potential.