Osmium impregnation of the Golgi apparatus

TLDR

The Golgi complex is a polarized, heterogeneous organelle composed of vesicles, vacuoles, and flattened cisternae, with distinct polarity observed across diverse cell types such as mouse epididymis epithelial cells, Brunner’s gland, and intestinal plasma cells. This study uses classical osmium impregnation to more precisely localize osmium reduction sites within the Golgi and compare their distribution to morphological indicators of polarity. Tissues were fixed in 1.3 % osmium tetroxide buffered with s‑collidine and then osmicated in 2 % aqueous osmium tetroxide for 40 h at 40 °C. Osmium consistently accumulated in the cisternae and vesicles on one side of the Golgi in all three cell types, confirming a selective, bipolar distribution and suggesting that reduction occurs at the inner face of the outer cisternae and vesicle membranes.

Abstract

Abstract The Golgi complex consists of a heterogeneous assemblage of small vesicles, larger vacuoles and characteristic packets of flattened cisternae morphologically distinct from other membranous organelles of the cytoplasm. It is polarized with respect to its position in the cell and also shows recognizable polarity in the arrangement of structural components within the complex. This polarity holds for cells in which the Golgi complex seems to have quite different functions, such as in the epithelial cells of mouse epididymis and of Brunner's gland, and plasma cells in the lamina propria of the intestine examined in this study. The present investigation employs a classical method for impregnation of the Golgi apparatus with the objective of more accurately localizing with the electron microscope the sites of osmium reduction within this heterogeneous organelle and of comparing the distribution of these sites with morphological indications of polarization within the Golgi lamellar systems. The osmium impregnation procedure generally used in this study consisted of fixing the tissues in 1.3% osmium tetroxide buffered with s‐collidine followed by osmication in 2% aqueous osmium tetroxide for 40 hours at 40°C. After osmication the three cell types studied consistently exhibited a selective localization of osmium in the cisternae and vesicles on one side of the Golgi complex. The observations that only the outer vesicles and cisternae contain osmium while other cytologically similar elements under the same conditions do not, emphasizes the heterogeneous, bipolar nature of the Golgi apparatus. The substances responsible for osmium reduction are quite dependent on the local environment provided are apparently formed during the prolonged phase of the exposure of the tissue to osmium and are most likely localized at the inner face of the membrane of the outer cisternae and vesicles.