Studies of protein metabolism in intestinal epithelial cells.

Abstract

Some aspects of intracellular protein metabolism can be studied with radioactive amino acids. Most previous studies of intestinal cells have involved measurements of incorporation of amino acids into fractions of the entire mucosa (1) and have provided composite measurements of protein synthesis in the tissues. The gastrointestinal mucosa contains numerous connective tissue elements, blood cells, smooth muscle and nerve cells, and several kinds of epithelial cells. In the small bowel the epithelial cells are of four types: Paneth, argentaffine, principal, and goblet cells; the principal cells themselves include proliferating, and differentiating or mature cells. All of these elements synthesize protein, but they synthesize different kinds of protein at different rates. It is desirable to define amino acid incorporation and protein synthesis with respect to particular tissue elements. This can be done by autoradiographic methods. The feasibility and value of this approach have been demonstrated by Leblond, Everett and Simmons (2), using radioactive methionine. In the present study leucine has been used, labeled with tritium for autoradiographic studies, and with C14 for concomitant radiochemical analyses. The kinetics of incorporation, the differences in rate of uptake between cells as well as within cells, and the further fate of incorporated leucine have been studied in some detail. Normal mice were used, as well as mice subjected to protein starvation and to steroid treatment.