High-Resolution Autoradiography of Newly Formed Proteins in the Epididymis After Incorporation of Tritiated Amino Acids

Abstract

The synthesis and excretion of newly formed proteins in the principal cells of the head, body, and tail of the epididymis were studied by quantitative autoradiography in light and electron microscopy. Adult mice were killed from 5 min to 6 hr after intravenous injection of tritiated leucine, lysine, and arginine. The labels were taken up early and in greater amounts in the principal cells of the head. Radioactivity decreased in the cells of all three segments throughout the first hour following administration of the tracers. Thereafter, it increased in the lumen. High-resolution analysis showed successive peaks of relative concentration of the labels over the endoplasmic reticulum, Golgi apparatus, and apical plasma membrane, thus confirming that protein synthesis and excretion follow the usual pathway in the principal cells all along the epididymis. However, since a radioactivity peak occurred as early as 15 min over the apical membrane of cells in the head, it is likely that part of the endoplasmic reticulum—canalicular and poor in polysomes—is involved independently in the synthesis and rapid transport of newly formed proteins.

Key Words:

• Epididymis
• Proteins
• Autoradiography
• Mice
• Electron microscopy.