Figure 7.

Inhibition by NPPB, furosemide, and sucrose of the sorbitol-induced hemolysis. (A) Enriched trophozoide-infected erythrocytes were incubated (10 min/21°C) in isosmotic sorbitol solution in the presence of increasing concentrations (0.01–100 μM) of NPPB (open triangles; ±SE, n = 12) or furosemide (closed triangles, ± SE; n = 9). Incubation was stopped by centrifugation and hemolysis was indicated by hemoglobin in the supernatant. In the insert on the right are the scanned images of supernatants from an individual experiment. The hemoglobin concentration of the supernatant for each condition (NPPB and furosemide) was determined photometrically (546 nm). Data are expressed as the percentage of the 100μM NPPB inhibited fraction (maximal inhibition = 86 ± 2% of total hemolysis, left). (B) Substrate competition of the infection-induced sorbitol hemolysis. Hemolysis (10 min/21°C) was assessed in solutions where different quantities of sorbitol (0–120 mosM) have been isosmotically replaced by sucrose (circles) or NaCl (squares). Mean normalized hemolysis (±SE; n = 8; left) and imaged supernatants of an individual experiment (right) are shown as in A. (C) Uptake of [¹⁴C] sorbitol into P. falciparum–infected human erythrocytes incubated in isosmotic sorbitol solution. The uptake of radiolabeled sorbitol was measured after 5, 30, 60, 90 and 120 s of incubation. Individual data of three experimental series were expressed as a percentage of the respective 2 min values and averaged (means ± SE; n = 4–12). (D) Inhibition of [¹⁴C] sorbitol uptake in isoosmotic sorbitol by sucrose. Mean uptake (±SE; n = 9–10) of [¹⁴C] sorbitol (30 s values minus the 5 s blank value) in isosmotic sorbitol solution (control) or in sorbitol solutions where 20 and 60 mM of sorbitol were replaced by 20 and 60 mM of sucrose or 10 and 30 mM of NaCl, respectively (uptake conditions: 3.7 × 10⁴ Bq/ml [¹⁴C] sorbitol, 2.5% final hematocrit, >90% parasitemia). * and # correspond to P ≤ 0.01 and 0.05, respectively, ANOVA.