Excitation and detection of action potential-induced fluorescence changes through a single monomode optical fiber

An optical probe capable of detecting intracellular potential changes in individual cells, in vitro, which has the potential for in vivo applications, has been developed. A single-mode optical fiber directs laser light onto cells stained with the voltage-sensitive fluorescent dye, WW781 and also returns part of the resulting fluorescence to a detection system. Frog cardiac cells in vitro were used in these initial experiments. The fractional change in fluorescent intensity of 10(-3) for a 50 mV shift in transmembrane potential obtained from a heart immobilized in zero calcium Ringer's solution is comparable to that reported for other optical methods. For hearts in normal calcium Ringer's solutions, very large reproducible motion related artifacts were detected.