title: High-Speed Electron Microscope Autoradiographic Studies of Diffusible Compounds1,2.
abstract: Three important factors are necessary for successful electron microscope autoradiography (EM-ARG): good resolution, proper preparation of the radioactive isotope (RI) labeled diffusible compounds, and shortened exposure time for ARG. The resolution problem is fundamental to EM-ARG. However, unless the diffusible RI compounds have been fixed correctly in the tissues during preparation, good resolution is useless. It is also necessary to shorten the exposure time for ARG. As yet, a high-speed ARG method for electron microscopy has not been reported, although scintillation ARG methods have been applied to macro- and micro-ARG since 1960. High specific activity, a large amount of radioactivity per unit exposure for radio incorporation (incubation), and careful selection of labeled compounds that concentrate in the DNA or RNA of cell organelles may increase the sensitivity of the emulsion and shorten the exposure time for ARG. For example, labeled thymidine accumulates in nuclear DNA, 3H-SPG (Schizophyllan-produced polyglucan) is incorporated into lysosomal granules, and labeled iodine concentrates in thyroid follicles, often increasing the sensitivity of the emulsion and shortening the exposure time. High-speed ARG yields good data in a very short time, but high-resolution ARG continues to be necessary, even though it requires 4 weeks or more of exposure time. Scintillation autoradiography using tritium seems unstable. We propose a new way to shorten exposure time for EM-ARG, by combining overdevelopment with coating both sides of the grid with emulsion. This method is approximately 100 times more sensitive than the conventional method, and only 4 days of exposure time are required, in contrast to the 1 month usually needed.
authors.affiliation: Department of Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo-Ku, Yushima, Tokyo 113, Japan.
authors.forename: Vinci
authors.initials: V
authors.lastname: Mizuhira
authors.affiliation: Department of Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo-Ku, Yushima, Tokyo 113, Japan.
authors.forename: Michiko
authors.initials: M
authors.lastname: Shiihashi
authors.affiliation: Department of Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo-Ku, Yushima, Tokyo 113, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Futaesaku
keywords: Chemical fixation for ARG; Diffusible compounds.; High-speed EM-ARG