Plasmodium berghei: ionic regulation and the induction of gametogenesis

The role of ionic regulation in the induction of gametogenesis of Plasmodium berghei at 20 degrees C was investigated. A potent inhibitor of Na+/H+ exchange, amiloride, strongly inhibited exflagellation and subsequent ookinete formation induced by RPMI 1640 with 10% fetal calf serum at pH 8.0, whereas Na+ or K+ channel inhibitors, H(+)-ATPase inhibitors, and a protonophore had no significant effect. Amiloride-treated 'activated' microgametocytes synthesized DNA to levels consistent with the expected 8C, but failed to develop further. These results may suggest that an increase in intracellular pH induced by Na+/H+ exchange plays an important role in the induction of gametogenesis by cultivating at pH 8.0 and 20 degrees C. Cultivation at pH 8.0 and 37 degrees C did not induce the development, and microgametocytes remained as nonactivated forms, having the DNA content of 1.5C. By culturing at pH 7.3 and 20 degrees C, however, most of microgametocytes finished synthesis of DNA up to the 8C level, but ceased development at various stages. Additionally, exflagellation occurred in a simple medium composed of buffered saline with 10 mM glucose. Glucose was indispensable for exflagellation, presumably acting as an energy source. Exflagellation induced by this solution was also inhibited by amiloride. It is therefore suggested that the induction of microgametogenesis may be composed of two distinct mechanisms, one is a temperature-dependent DNA synthesis and the other is a pH-dependent control of developmental events leading to microgamete assembly and exflagellation.