Improved indicators of cell membrane potential that use fluorescence resonance energy transfer

Background: Fluorescence detection of cell membrane potentials is an important technique in neurobiology, cell physiology and pharmaceutical screening, but traditional one-fluorophore indicators either respond too slowly or have limited sensitivity. Recently, we introduced two-component sensors based on the transfer of fluorescence resonance energy from fluorescent lectins bound on one side of the plasma membrane to highly fluorescent oxonol accepters that electrophorese from one face of the membrane to the other in response to membrane potential. Results: We have found that fluorescent lectins can often be advantageously replaced in such sensors by fluorescently labeled phospholipids. A coumarin-labeled phosphatidylethanolamine donor and a bis(1,3-dihexyl-2-thiobarbiturate)trimethineoxonol acceptor gave the largest sensitivity of fluorescence ratio (>50% per 100 mV) ever reported. The response was also speeded severalfold by lengthening the mobile dye to the pentamethineoxonol analog, the <0.4 ms time constant of which was shorter than action potential durations. Photodynamic damage due to singlet oxygen was reduced by administering a natural carotenoid, astaxanthin, Conclusions: Voltage-sensitive fluorescence resonance energy transfer already gives record-setting performance on single cells and will continue to be rationally improvable.