2023 年 37 巻 2 号 p. 145-154
The lipid bilayer is the essential component of the cell membrane to provide some structural support for a cell and control transport of materials entering and exiting the cell. Since it has a centrosymmetric structure, the second harmonic generation (SHG) signal can hardly be observed from the membrane. Adding a dye to the lipid molecules in outside layer makes the lipid bilayer non-centrosymmetric and enables it to generate observable SHG signals. Physical disturbances of the membrane would lead to reallocation and transmembrane migration of molecules including dyes, thereby making the lipid layer structure homogeneous and centrosymmetric and consequently diminishing the SHG signal. If so, a change in the membrane structure could be imaged based on the SHG signal intensity. The present study therefore aims to seek for a feasibility of imaging the membrane damage via SHG signal measurement. Moreover, the present study investigates how the SHG signal change varies depending on the frequency of electric stimulations that are used as a damage source. Liposomes were used as a cell membrane model. The SHG signal intensity of liposomes loaded with the SHG-specific dye, Ap3, during electric stimulations was observed using a multiphoton microscope. The results demonstrated that the SHG signal intensity of the membrane decreased with the repetitive application of the electric pulse. While the SHG signal decay was faster as the time interval between consecutive electric pulses was shorter, no remarkable decay was found for longer time intervals. The trend was explained by membrane healing or pore resealing during a time interval between consecutive electric pulses which prevented transmembrane migration of Ap3. The results suggested that the membrane structure change could be imaged based on the SHG signal measurement.
