Two-color fluorescent probes for imaging the dipole potential of cell plasma membranes.

The dipole potential (Psi(d)) constitutes a large and functionally important part of the electrostatic potential of cell plasma membranes. However, its direct measurement is not possible. Herein, new 3-hydroxyflavone fluorescent probes were developed that respond strongly to Psi(d) changes by a variation of the intensity ratio of their two well-separated fluorescence bands. Using fluorescence spectroscopy with cell suspensions and confocal microscopy with adherent cells, we showed, for the first time, two-color fluorescence ratiometric measurement and visualization of Psi(d) in cell plasma membranes. Using this new tool, a heterogeneous distribution of this potential within the membrane was evidenced.