Table 1. Values of ΔpH, Δψ and Δp under various conditions.

Potentials were determined using a TPMP⁺ electrode as described in the Materials and methods section. Standard incubation conditions were 120 mM KCl, 3 mM HEPES, 1 mM EGTA, 0.3% (w/v) BSA (pH 7.2 and 37 °C), 50 μg of PHPA·ml⁻¹, 4 units·ml⁻¹ horseradish peroxidase, 30 units·ml⁻¹ SOD and 1.875 μM TPMP. Where shown, 4 mM succinate, 4 μM rotenone, 2 μM piericidin, 2 μM FCCP and 100 nM nigericin were added. Values are means±S.E.M. for measurements on four to ten separate mitochondrial preparations. *Significant (P<0.001) difference from succinate. We define ΔpH as zero in the presence of nigericin.

	Δψ (mV)	ΔpH (mV)	Δp (mV)
Succinate	141±4	40±5	181±5
Succinate+rotenone	139±4	41±4	180±4
Succinate+piericidin	147±3	40±3	187±3
Succinate+FCCP	0±0*	0±0*	0±0*
Succinate+nigericin	181±5*	0	181±5