Mitochondrial Membrane Potential (ΔΨ) Fluctuations Associated with the Metabolic States of Mitochondria

The proton electrochemical gradient generated by the respiratory chain activity accounts for over 90% of the available respiratory energy, and, as such, its evaluation and accurate measurement regarding total values and fluctuations are an invaluable component of the understanding of mitochondrial function. Consequently, alterations in electric potential across the inner mitochondrial membrane generated by differential protonic accumulation and transport is known as the mitochondrial membrane potential, or ΔΨ, and is reflective of the functional metabolic status of mitochondria. There are several experimental approaches to measure ΔΨ, ranging from fluorometric evaluations to electrochemical probes. Here, we will expose a particular method for ΔΨ evaluation, which is dependent on the movement of a particular ion, tetraphenylphosphonium (TPP⁺) with a selective electrode. The evaluation of the accumulation and movements of TPP⁺ across the inner mitochondrial membrane is a sensitive, immediate, accurate, and simple method of evaluation of ΔΨ in isolated, respiring mitochondria.