Synthesis, Transport and Secretion of Protein in the Initial Segment of the Mouse Epididymis as Studied by Electron Microscope Radioautography

Abstract

Adult male mice were administered [3H]-leucine and samples of the initial segment of the epididymis were prepared for light and EM radioautography after intervals ranging from 10 min-12 h. Light microscope radioautography revealed labeling of the principal cells of the epididymal epithelium and radioactivity appeared in the epididymal lumen 2 h after injection of [3H]-leucine. Luminal labeling was not abolished by prior ligation of the ductuli efferentes. Analysis of EM radioautographs of principal cells demonstrated successive peaks in the percent of grains and in relative grain concentrations over the rough endoplasmic reticulum at 10 min and the Golgi apparatus at 1 h after injection of precursor. A high proportion of grains was associated with the smooth endoplasmic reticulum at all intervals, but its relative grain concentration did not reach the values attained by the rough endoplasmic reticulum and Golgi apparatus. Luminal labeling was mainly associated with material lying between spermatozoa. The rough endoplasmic reticulum and the Golgi apparatus of the principal cells were apparently involved in synthesis and transport of protein. Approximately 2 h were required for intracellular events in epididymal protein secretion. Suggestions as to the role of the smooth endoplasmic reticulum are presented. The mode of release of secretory protein remains uncertain.