Monitoring of the mitochondrial and plasma membrane potentials in human fibroblasts by tetraphenylphosphonium ion distribution

The lipophilic cation tetraphenylphosphonium (TPP⁺) is accumulated by human skin fibroblasts across both the plasma and mitochondrial membranes. We show here that TPP⁺ uptake is indeed greatly decreased under conditions leading to de-energization of mitochondria. The TPP⁺ accumulation in the presence of the proton ionophore FCCP has been used for determination of the plasma membrane potential across the plasma membrane, after correction for potential-independent binding of TPP⁺ to cellular components. Following this procedure, a value of 75 mV has been obtained. Through the amount of TPP⁺ released by FCCP treatment, an estimate of thein situ mitochondrial membrane potential has been made. Furthermore, we report that the mitochondrial component of TPP⁺ accumulation decreases with aging of fibroblast cultures.Abbreviations _m membrane potential across thein situ mitochondria - _p membrane potential across the plasma membrane - TPP⁺ tetraphenylphosphonium - HEPES N-2-hydroxyethylpiperazineN-2-ethanesulfonic acid - FCCP carbonyl cyanidep-trifluoromethoxyphenylhydrazone