Relationship of incorporation of radioprecursors into protein and phospholipids of the plasmalemma of Guinea pig (neonate) intestinal epithelium and the cessation of uptake of macromolecules (closure).

The incorporation of radioprecursors into intestinal epithelial cell proteins and phospholipids was studied to assess the role of protein and phospholipid synthesis and/or turnover in the cessation of the absorption of macromolecules (closure). Radiophosphorus incorporation into cellular phospholipids was enhanced when pinocytosis was stimulated. The specific activity of cellular and brush border phospholipids and specific phosphatides increased during the period of active endocytosis. No alteration in specific phosphatide percent composition was observed. Radioamino acid incorporation into cellular protein was not influenced by age. These data are consistent with the idea that the period of active macromolecule absorption by the guinea pig intestinal epithelium is defined by the exhaustion of membrane available for endocytosis.