Second-harmonic generation sensitivity to transmembrane potential in normal and tumor cells

Second-harmonic generation (SHG) is emerging as a powerful tool for the optical measurement of transmembrane potential in live cells with high sensitivity and temporal resolution. Using a patch clamp, we characterize the sensitivity of the SHG signal to transmembrane potential for the RH 237 dye in various normal and tumor cell types. SHG sensitivity shows a significant dependence on the type of cell, ranging from 10 to 17% per 100 mV. Furthermore, in the samples studied, tumor cell lines display a higher sensitivity compared to normal cells. In particular, the SHG sensitivity increases in the cell line Balb/c3T3 by the transformation induced with SV40 infection of the cells. We also demonstrate that fluorescent labeling of the membrane with RH 237 at the concentration used for SHG measurements does not induce any measurable alteration in the electrophysiological properties of the cells investigated. Therefore, SHG is suitable for the investigation of outstanding questions in electrophysiology and neurobiology.