Figure 9.  DY and DpH are opposing forces with respect to each other.  As discussed above in relation to Fig. 7, valinomycin collapses DY with an increase in DpH (i.e. more acetate is accumulated), and nigericin collapses DpH with an increase in DY (more TPP⁺ is accumulated).  This phenomenon occurs because DY (interior negative) acts to suppress the magnitude of DpH (interior alkaline) since positively charged protons are pulled back into the internal space, and when valinomycin is present, this suppressive force is removed.  Conversely, DpH acts to decrease DY because protons move down their concentration gradient into the internal space which is interior alkaline, thereby decreasing extrusion of positive charge.  In the presence of nigericin, this negative force is removed, allowing DY to increase. 

In mitochondria, these effects are also due to a phenomenon called “respiratory control”.  Unlike E. coli or RSO membrane vesicles, in mitochondria, the rate of respiration (i.e., proton pumping) is controlled by the magnitude of (i.e., the higher , the lower the rate of respiration).  Valinomycin increases the rate of respiration, but the increase cannot be expressed as an increase in DY due to the presence of the ionophore, so DpH increases; the situation is vice versa for nigericin.