Subcellular Particles: A Symposium Held during the Meeting of the Society of General Physiologists at the Marine Biological Laboratory, Woods Hole, Massachusetts, June 9-11, 1958

By Teru Hayashi | Go to book overview

Functional Changes in the Structure of Cell Components

GEORGE E. PALADE Rockefeller Institute for Medical Research New York, N. Y.

PHYSIOLOGICAL EVENTS THAT OCCUR at the intracellular level are frequently accompanied by structural changes which deserve careful study because they may suggest, and sometimes indicate, the role played by the affected structures in the general economy of the cell. As the functional significance of many cell components is still uncertain or entirely unknown, suggestions or indications of this kind can be particularly valuable. Changes or modulations in cell structure occur at various dimensional levels and some of them are so striking that they were noted early in light microscopy and studied with considerable profit. A conspicuous example is represented by the extensive changes in form and distribution undergone by the nuclear material during cell division. Our knowledge of the mechanisms operating in hereditary transmission has, in fact, been derived from a detailed analysis of such structural changes, correlated with a careful study of the qualities of the products, in this case the offspring.


FUNCTIONAL CHANCES IN EXOCRINE CELLS OF PANCREAS

Heidenhain's Hypothesis. Another example, closer to the subject to be discussed in the following pages, concerns the exocrine cells of the pancreas. As early as 1875, Heidenhain (11) noted that the numerous granules which occupy the apical region of these cells disappear shortly after food intake, to be replaced by apparently new granules a few hours later. By following in time the changes occurring in the apical pole of the exocrine cells, on the one hand, and the variations in the enzymatic activity of the pancreatic juice, on the other hand, Heidenhain arrived at the conclusion that the granules consist of digestive enzyme precursors. His conclusion rested on the finding that the disappearance of these intracellular bodies, which he called zymogen granules (12), coincided in time with the appearance of proteolytic enzymes in the pancreatic juice. According to his interpretation, the zymogen granules represent a temporary intracellular storage of digestive enzymes which will be released from the cell at a future food intake. For many years the cyclic variation in the number of zymogen granules discovered by Heidenhain remained the only well established and clearly understood event in the physiology of the pancreatic exocrine cell. No real progress was

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Subcellular Particles: A Symposium Held during the Meeting of the Society of General Physiologists at the Marine Biological Laboratory, Woods Hole, Massachusetts, June 9-11, 1958
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