FACTORS AFFECTING EXFLAGELLATION OF IN-VITRO CULTIVATED PLASMODIUM-FALCIPARUM GAMETOCYTES

The environment of Plasmodium falciparum gametocytes changes when they make the transition from the vertebrate to the invertebrate host. Gam etocytes of this species cultivated in vitro were used to evaluate the effect of serum, pH, pCO2 tension, bicarbonate ion, and temperature o n gamete formation. Temperature was the only factor responsible for ke eping P. falciparum gametocytes in the inactivated state. Mature gamet ocytes held at temperatures above 30-degrees-C remained quiescent in 1 0% serum, even at low ambient pCO2, tension, alkaline pH, and in the p resence of 25 mM bicarbonate ion. When the temperature of the medium w as allowed to drop below 30-degrees-C, gametocytes emerged from the re d blood cells and microgametocytes consistently exflagellated at pH 7. 4, even in the absence of bicarbonate ion. With regard to bicarbonate ion, exflagellation in P. falciparum is similar to P. berghei and diff erent from P. gallinaceum gametocytes, which have an obligate requirem ent for bicarbonate ion.