Characterization of two putative potassium channels in Plasmodium falciparum.

Potassium channels are essential for cell survival and participate in the regulation of cell membrane potential and electrochemical gradients. During its lifecycle, Plasmodium falciparum parasites must successfully traverse widely diverse environmental milieus, in which K+ channel function is likely to be critical. Dramatically differing conditions will be presented to the parasite in the mosquito mid-gut, red blood cell (RBC) cytosol and the human circulatory system. In silico sequence analyses identified two open-reading frames in the P. falciparum genome that are predicted to encode for proteins with high homology to K+ channels. To further analyse these putative channels, specific antisera were generated and used in immunoblot and immunofluorescence analyses of P. falciparum-infected RBCs. Recombinant genome methods in cultured P. falciparum were used to create genetic knock outs of each K+ channel gene to asses the importance of their expression. Immunoblot and IFA analyses confirmed the expression of the two putative P. falciparum K+ channels (PfK1 and PfK2). PfK1 is expressed in all asexual stage parasites, predominantly in late stages and localizes to the RBC membrane. Conversely, PfK2 is predominantly expressed in late schizont and merozoite stage parasites and remains primarily localized to the parasite. Repeated attempts to knockout PfK1 and PfK2 expression by targeted gene disruption proved unsuccessful despite evidence of recombinant gene integration, indicating that pfk1 and pfk2 are apparently refractory to genetic disruption. Putative K+ channel proteins PfK1 and PfK2 are expressed in cultured P. falciparum parasites with differing spatial and temporal patterns. Eventual functional characterization of these channels may reveal future pharmacological targets.