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Phase Transition of Plasma Membranes of Rat Hepatocyte and Hepatoma Cells by Electron Diffraction¹

Electron Optics Laboratory, Roswell Park Memorial Institute, Buffalo, New York 14263

The transition temperatures (T_c) of the plasma membranes of Reuber H-35 hepatoma and normal ACI rat hepatocytes were measured by electron diffraction under physiological conditions. Diffraction rings below T_c indicate the existence of solid lipid domains. The T_c of both membranes increase to a plateau value of 17.5° during the storage period of 4 days at 4°, the rate of increase being slower for normal liver membranes. The extrapolations to zero storage suggest an innate difference of T_c for these two membranes. Storage in oxygen-reduced media slows down the initial increase of T_c in normal liver membranes, while the depletion of divalent cations accelerates the increase. Differences in lipid composition are partly responsible for this behavior.

¹ This work is supported by NIH Grant CA-15330 from the National Cancer Institute.

² Recipient of NIH Career Development Award 1 K04 CA-00084.

Received 8/29/75. Accepted 2/12/76.