PSAC activity on RBCs from CFTR^{ΔF508/ΔF508} donors. (A) Single-channel recordings on an RBC from a CFTR^{ΔF508/ΔF508} donor infected with a trophozoite-stage parasite. Bath and pipette contained solution A. V_m was +100 or -100 mV (upper and lower traces, respectively). Closed channel levels are indicated by dashed red lines. (B) Recording from a 2-channel patch on an infected CFTR^{ΔF508/ΔF508} RBC in solution A at a V_m of -100 mV. Downward transitions represent the opening of either one or both channels; corresponding levels are marked with dotted lines. (C) Whole-cell recording on an infected CFTR^{ΔF508/ΔF508} RBC with near physiologic bath and pipette solutions of 165 mM NaCl, 10 mM MgCl₂, 5 mM CaCl₂, 20 mM Na-HEPES, pH 7.4, before or after addition of 200 μM furosemide (left and right groups, respectively). (D) Whole-cell currents with solution A in bath and pipette from infected RBCs using healthy (left traces) and CFTR^{ΔF508/ΔF508} donors (right traces). In panels C and D, traces for 50-ms steps to V_m between -100 mV and +100 mV in 20-mV increments are superimposed to demonstrate PSAC's voltage dependence; the zero current levels are marked with horizontal red lines. Scale bars represent 2.9 pA/127 milliseconds (A), 3.1 pA/500 ms (B), 1590 pA/30 ms (C), and 3000 pA/30 ms (D). Similar PSAC activity was recorded from each of 6 CFTR^{ΔF508/ΔF508} donors after in vitro parasite culture.