Fig 1.

Sheep erythrocytes are susceptible to the pore-forming activity of ApxIA and CyaA in a concentration-dependent manner. Sheep erythrocytes (5 × 10⁸/ml) in HBSS buffer were incubated at 37°C in the presence of different concentrations of ApxIA (A) and CyaA (B). Hemolytic activity was measured as the amount of released hemoglobin by photometric determination (A₅₄₁). The results represent average values from two independent experiments performed in duplicate. (C) Typical current traces of ApxIA and CyaA in asolectin lipid bilayers in 1 M KCl, 10 mM Tris, and 2 mM CaCl₂ (pH 7.4). The ApxIA and CyaA concentration was 1 nM. Traces were recorded 60 s after ApxIA or CyaA addition. The applied membrane potential was 55 mV; the temperature was 25°C. All recordings were filtered at 100 Hz. The detailed recording of CyaA pores was performed at a higher current resolution. (D) The conductance of single ApxIA or CyaA pores was determined in 1 M KCl, 10 mM Tris, and 2 mM CaCl₂ (pH 7.4) at membrane potentials of between 50 and 75 mV; the temperature was 25°C.