The Plasmodium falciparum-induced anion channel of human erythrocytes is an ATP-release pathway

Infection with the malaria parasite Plasmodium falciparum induces osmolyte and anion channels in the host erythrocyte membrane involving ATP release and autocrine purinergic signaling. P. falciparum-parasitized but not unstimulated uninfected erythrocytes released ATP in a 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB; 7 A mu M)-sensitive and serum album (SA; 0.5% w/v)-stimulated manner. Since Plasmodium infection of human erythrocytes induces SA-dependent outwardly (OR) and SA-independent inwardly rectifying (IR) anion conductances, we tested whether the infection-induced OR channels directly generate an ATP release pathway. P. falciparum-parasitized erythrocytes were recorded in whole-cell mode with either Cl- or ATP as the only anion in the bath or pipette. In parasitized cells with predominant OR activity, replacement of bath NaCl by Na-ATP (NMDG-Cl pipette solution) shifted the current reversal potential (V (rev)) from -2 A +/- 1 to +51 A +/- 3 mV (n = 15). In cells with predominant IR activity, in contrast, the same maneuver induced a shift of V (rev) to significantly larger (p a parts per thousand currency signaEuro parts per thousand 0.05, two-tailed t test) values (from -3 A +/- 1 to +66 A +/- 8 mV; n = 5) and an almost complete inhibition of outward current. The anion channel blocker NPPB reversibly decreased the ATP-generated OR currents from 1.1 A +/- 0.1 nS to 0.2 A +/- 0.05 nS and further shifted V (rev) to +87 A +/- 7 mV (n = 12). The NPPB-sensitive fraction of the OR reversed at +48 A +/- 4 mV suggesting a relative permeability of P (ATP)/P (Cl) a parts per thousand aEuro parts per thousand 0.01. Together, these data raise the possibility that the OR might be the electrophysiological correlate of an erythrocyte ATP release pathway.