Assessing the Mitochondrial Membrane Potential in Cells and In Vivo using Targeted Click Chemistry and Mass Spectrometry

The mitochondrial membrane potential (Δψ(m)) is a major determinant and indicator of cell fate, but it is not possible to assess small changes in Δψ(m) within cells or in vivo. To overcome this, we developed an approach that utilizes two mitochondria-targeted probes each containing a triphenylphosphonium (TPP) lipophilic cation that drives their accumulation in response to Δψ(m) and the plasma membrane potential (Δψ(p)). One probe contains an azido moiety and the other a cyclooctyne, which react together in a concentration-dependent manner by “click” chemistry to form MitoClick. As the mitochondrial accumulation of both probes depends exponentially on Δψ(m) and Δψ(p), the rate of MitoClick formation is exquisitely sensitive to small changes in these potentials. MitoClick accumulation can then be quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This approach enables assessment of subtle changes in membrane potentials within cells and in the mouse heart in vivo.