Mitochondrial membrane potential fluorescent assays estimate ΔΨm in living cells using lipophilic cationic dyes such as TMRM, TMRE, rhodamine 123, and JC-1, which accumulate in mitochondria according to membrane polarization; loss of signal after FCCP or CCCP treatment is interpreted as mitochondrial depolarization. TMRM/TMRE and rhodamine 123 are commonly used for semi-quantitative live-cell microscopy or flow cytometry, while JC-1 can report a shift from red aggregate fluorescence to green monomer fluorescence during depolarization; interpretation requires controls because dye concentration, quenching mode, cell type, dye efflux, and mitochondrial mass can affect fluorescence independently of ΔΨm.
Electrochemical and Membrane Potential Detection
Core technologies in electrochemistry and membrane potential detection aim to precisely assess the electrophysiological state and barrier integrity of biological membranes across multiple dimensions, ranging from the cell surface to the interior of organelles. Techniques such as fluorescent plasma membrane potential dye detection and neuronal voltage-sensitive dye imaging enable the real-time capture of millisecond-scale transient potential changes and nerve impulse conduction. Regarding the macroscopic electrical activity of complex tissues, cardiac voltage-sensitive optical mapping allows for the dynamic visualization of electrophysiological activity in intact myocardial tissue. Furthermore, fluorescent detection of mitochondrial membrane potential provides critical indicators for evaluating cellular energy metabolism and early-stage apoptosis. Finally, transepithelial/transendothelial electrical resistance (TEER) measurement technology is used to quantitatively assess the barrier permeability and structural integrity of epithelial or endothelial cell layers.
Related Experimental Schemes
Cardiac voltage-sensitive optical mapping records changes in transmembrane potential from cardiac tissue by staining the preparation with a voltage-sensitive dye and imaging fluorescence changes during electrical activation; the resulting optical action potentials can be used to map activation time, action potential duration, conduction velocity, wavefront propagation, and arrhythmia dynamics. The optical signal represents a relative fluorescence change from a tissue volume rather than a single-cell intracellular recording, so spatial resolution, sampling rate, voltage resolution, optical magnification, light penetration, and motion control must be considered together when interpreting optical action potentials.
Neuronal voltage-sensitive dye imaging detects membrane-potential-dependent optical changes from dyes associated with neuronal membranes, enabling optical recording of electrical activity from single neurons, dendrites, axons, spines, or neuronal populations in brain slices and cultured neurons. VSD signals are typically reported as fractional fluorescence or absorbance changes over baseline, such as ΔF/F or ΔI/I, and published protocols use high-speed cameras or photodiode arrays because neuronal voltage signals occur on millisecond time scales. Fast VSD imaging can be applied at two common scales: bulk staining of brain slices to measure circuit-level spatiotemporal activity, and single-cell loading or biolistic delivery to record membrane-potential transients from individual neuronal compartments. Optical signals should be interpreted as membrane-potential-related readouts, and validation by simultaneous electrophysiology or pharmacological controls is recommended when the experimen
Fluorescent plasma-membrane potential dye assays measure changes in cell membrane potential using voltage-sensitive dyes whose fluorescence changes when cells depolarize or hyperpolarize. Anionic bis-oxonol dyes such as DiBAC4(3) enter depolarized cells more readily and show increased fluorescence after intracellular binding, while hyperpolarization reduces dye accumulation and fluorescence. FMP/FLIPR membrane-potential dyes are used for faster, homogeneous microplate assays of ion-channel or receptor-mediated membrane-potential changes.
TEER measures electrical resistance across epithelial or endothelial monolayers cultured on permeable supports, and the readout reflects ionic conductance through the cell barrier, especially the paracellular pathway regulated by junctional integrity. TEER can be measured without destroying the monolayer and is commonly used before or during transport, permeability, barrier-disruption, and barrier-maturation experiments. TEER values are influenced by biological maturation and technical conditions; reported factors include temperature, medium formulation, passage number, electrode geometry, membrane properties, and junctional length during early monolayer maturation. Therefore, TEER should be interpreted with blank-insert subtraction, area normalization, repeated readings, and, when possible, orthogonal barrier readouts such as FITC-dextran flux or tight-junction staining.
