[Erroneous use of lipophilic phosphonic cations for determining mitochondrial membrane potential].

The energy-dependent accumulation of triphenylmethylphosphonium (TPMP+) in rat liver mitochondria at 0 degrees C is less than that at a room temperature only by 30-50%, while the cation penetration rate drastically decreases thus making possible an accurate studying of the transport kinetics. It is shown that K+-diffusion potential accelerates the influx of TPMP+ and decreases the efflux rate in full agreement with the expected behaviour of a penetrating cation diffusing along or against the electrical field. On the contrary, the energization of mitochondria, which has been generally believed to generate a metabolic membrane potential, caused only a stimulation of the influx of TPMP+ without affecting the efflux rate. The TPMP+ efflux half-time was found to be about 3 minutes independently of the energetic state of mitochondria. This independence indicates that the energization is not accompanied by a rise of the membrane potential. The accumulation of TPMP+ by the energized mitochondria must be considered as an active process transporting lipophilic cations against the electrochemical gradient. It follows that the steady state distribution of TPMP+ cannot be a measure of the membrane potential in mitochondria.