An Electron Microscopic Demonstration of a Surface Pattern on the Plasma Membrane of Sectioned Intestinal Epithelium after Saponin Treatment

Abstract

A TRANSVERSE section of the plasma membrane, after osmium or permanganate fixation, appears in electron micrographs as a triple-layered structure, about 8 mµ thick, composed of two outer opaque layers separated by a clear layer¹. This unit membrane appears to be universal for all higher animal and plant cells and has been considered to represent the protein-lipid-protein molecular model as originally proposed for the plasma membrane by Danielli and Davson². Until the recent report by Dourmashkin, Dougherty and Harris³, little electron microscopic evidence had been produced to suggest heterogeneity on the plane surface of the plasma membrane. These authors demonstrated, however, that in vitro saponin treatment produced hexagonally arranged pits or holes in isolated membranes from erythrocytes, liver cells, Rous sarcoma cells and virus particles. The pits were seen in isolated membranes spread on grids after negative staining, and they state that they were unable to demonstrate these structures in sections of similarly treated liver cell membranes.