Dependence of Plasmodium falciparum in vitro growth on the cation permeability of the human host erythrocyte

Intraerythrocyte growth of the malaria parasite Plasmodium falciparum induces a Ca2+-permeable unselective cation conductance in the host cell membrane which is inhibited by ethylisopropyl-amiloride (EIPA) and is paralleled by an exchange of K+ by Na+ in the host cytosol. The present study has been,performed to elucidate the functional significance of the electrolyte exchange. Whole-cell patch-clamp experiments confirmed the Ca2+ permeability and EIPA sensitivity of the Plasmodium falciparum induced cation channel. In further experiments, ring stage-synchronized parasites were grown in vitro for 48 h in different test media. Percentage of Plasmodium-infected and phosphatidylserine-exposing erythrocytes was measured with FACS analysis by staining with the DNA-dye Syto16 and annexin V,respectively. The increase of infected cells was not significantly affected by an 8 h replacement of NaCl in the culture medium with Na-gluconate but was significantly blunted by replacent of NaCl with KCl, NMDG-Cl or raffinose. Half maximal growth was observed at about 25 mM Na+. The increase of infected cells was further inhibited by EIPA (IC50<10 mu M) and at low extracellular free Ca2+. Infected cells displayed significantly stronger annexin binding, an effect mimicked by exposure of noninfected erythrocytes to oxidative stress (1 mM t-butylhydroperoxide for 15 min) or to Ca2+ ionophore ionomycin ( 1 mu M for 60 min). The observations indicate that parasite growth requires the entry of both, Na+ and Ca2+ cations into the host erythrocyte probably through the EIPA sensitive cation channel. Ca2+ entry further induces break-down of the phospholipid a symmetry in the host membrane. Copyright (C) 2003 S. Karger AG, Basel.