Submicrosecond Imaging Under a Pulsed-Laser Fluorescence Microscope

A microscope system has been constructed that enables digital imaging of a fluorescent cell under pulsed illumination. Each image is produced by a single laser pulse of duration less than 0.3 µ s. With this system, microsecond responses of a single cell to an externally applied electric field have been resolved temporally and spatially. The cell membrane was stained with a voltage-sensitive fluorescent dye. The induction of transsmembrane potential by the applied field, and the perforation (electroporation) of the cell membrane under an intense field, were seen as successive images. The major finding was a transient increase, at the moment of perforation, in the membrane permeability to an enormous level in localized regions of the cell membrane. Possible roles in cell technology, as well as other applications of the microscope system, are discussed.