Figure 9. Effect of CPZ on oxonol VI fluorescence under Na⁺,Na⁺ exchange conditions.

Oxonol VI fluorescence was measured as described in Materials and Methods. The working volume in the cuvette throughout the measurement was 2–2.1 ml. The cuvette contained 30 mM histidine, 30 mM NaCl, 2 mM MgCl₂, and 20–30 µl proteoliposomes, and the experiment was started with the addition of 75 µM ATP. After reaching steady state, 20 µM CPZ dissolved in DMSO was added. A. Shown is the effect of addition of ATP and CPZ in the absence (black) or in the presence (red) of 25 µM ADP. The numbers indicate the percentage decrease in maximum fluorescence occurred by pretreatment with 25 µM ADP. Representative of four independent experiments is shown. B. The fluorescence response was measured as in panel A, but CPZ was added first, followed by the addition of ATP, as indicated by the arrows.