Figure 5.
Effect of pipette and bath osmolarity on Cl− whole-cell currents of P. falciparum–infected human erythrocytes. Inhibition by hyperosmotic addition of sucrose to the bath. (A) Cell volume change of a noninfected erythrocyte during continuous whole-cell recording in isosmotic NaCl bath solution (left), upon hypertonic cell shrinkage (+100 mM sorbitol; middle), and hypotonic reswelling (−50 mM NaCl; right). Ghost membrane is indicated by arrows. (B–D) Current traces recorded at different time points (as indicated) upon achievement of whole-cell recording mode. Records were obtained in noninfected (B) and infected erythrocytes (C and D) with hypertonic (B and D, ∼330 mosM) and hypotonic (C, ∼190 mosM) NMDG-Cl pipette solution. In these experiments, the noninfected and infected erythrocytes were permanently superfused with isosmotic NaCl bath solution. (E) Mean I-V relations (±SE) recorded as in C and D, 4 min after achievement of whole-cell configuration either with hypertonic (squares, n = 17), hypotonic (triangles, n = 5), or isotonic NMDG-Cl pipette solution (circles; n = 9). (F) I-V relations of the volume-sensitive current fraction Iswell-Ishrink as calculated from E by subtracting the currents recorded with hypotonic (∼190 mosM, n = 5) from those obtained with hypertonic (∼330 mosM, n = 17) NMDGCl pipette solutions. Currents were recorded with isotonic NaCl bath solution 4 min after achievement of whole-cell configuration. (G) Concentration-dependent inhibition of the outwardly rectifying Cl− current by sucrose. Current traces recorded from an infected cell before and immediately after addition of increasing concentrations of sucrose to the NaCl bath solution, and after wash-out of sucrose (NMDG-Cl pipette solution). Prior to the application of sucrose, cells were preshrunken by addition of NaCl (+25 mM) to the bath solution. (H) Mean I-V relations (±SE; n = 6) of the outwardly rectifying conductance recorded as in E under control conditions (NaCl bath; circles) and after addition of sucrose (400 mM) to the bath (triangles). In addition, the calculated sucrose-sensitive current fraction is shown (diamonds). (I) Mean relative outward conductances (±SE; n = 6) in the absence (control) and presence of increasing concentrations of sucrose in the bath solution (as indicated), and after replacement of sucrose by NaCl solution (wash-out). Conductances were calculated from (E and F) by linear regression of the outward current between +20 and +80 mV voltage.