The Endoplasmic Reticulum

Original Findings on Cultured MateriaL--The relatively short history of the endoplasmic reticulum started 10 years ago, in 1945, when Porter, Claude, and Fullam (1), noted the presence of a "lace-like" reticulum in the ground substance of ceils grown in tissue culture and examined in toto in the electron microscope. In describing their findings, these authors mentioned that "at higher magnifications vesicle-like bodies, that is elements presenting a center of less density and ranging in size from 100 to 150 m/z, appear arranged along the strands of the reticulum." In retrospect, it can be said that two of the main features of this new cytoplasmic system, namely (a) its reticular disposition and (b) the vesicular character of its component elements, were already clearly noted in its first description. In subsequent papers, Porter and his collaborators described the preferential concentration of the vesicular elements of the reticulum in the endoplasm, and their scarcity or absence in the supposedly exoplasmic periphery of the cytoplasm (2, 3), a finding which eventually led to the selection of "endoplasmic reticulum" as a name for the system. The term was first cautiously tried in a caption in 1948 (3) and finally used in an article published by Porter and Kallman in 1952 (4). I t appears that, at that time, our group was not yet engaged in large scale production of new cytological terms with a heavy Latin flavor, and was still proceeding with cautious restraint in matters of nomenclature. Besides the reticular disposition and the endoplasmic location implied in the name, Porter's studies established a number of other important features for the new cytoplasmic component, namely the usual continuity of the system throughout the endoplasm of normal cells, the remarkable polymorphism of its component elements, and the breaking down of the entire system in cytolysis into a collection of isolated vesicles. The Shift from Spread to Sectioned Cytological Specimens.--The information obtained from the study of cultured cells was presented by Porter in a final article in 1953 (5), at a time when new embedding and microtomy procedures