Unbuffered osmium staining in pars recta of the proximal tubule from rat kidney studied by thin and semi-thin section cytochemistry

Multitubular bodies in intestinal cells of Amphiuma means/tridactylum (Urodela): ultrastructural characterization

The jejunal absorptive cells of the salamander Amphiuma, when examined using transmission electron microscopy, were found to possess a unique type of intracellular vacuole containing membranous tubules. These vacuoles, tentatively named multitubular bodies, were located in the cytoplasm between the nucleus and the brush-border membrane, and were seen with greatest frequency in the summer and fall. The vacuoles containing multitubular bodies had an average diameter of 0.6 microns, and the membranous tubules within had an average diameter of 30 nm. The tubules differed morphologically from the vesicles in the multivesicular bodies, and from the primary lysosomes in the polylysosomal vacuoles. The tubules did not exhibit acid phosphatase activity, and were of similar diameter and membrane thickness as the Golgi saccules. In contrast to the multivesicular bodies, the multitubular bodies did not take up exogenous horseradish peroxidase. Early forms of autophagosomes resembling these vacuoles were often seen in the para-Golgi region of the cell. The multitubular bodies may represent a distinct type of autophagosome. Although the exact origin of the tubules as well as their role in cellular activity is unclear, their seasonal appearance within the multitubular bodies of the absorptive cells suggests a unique means of selective down-regulation of Golgi-like organelles.

Cytochemical studies on induced autophagocytosis in mouse exocrine pancreas

1. The origin of the limiting membranes of autophagic vacuoles (AVs) in mouse pancreatic acinar cells was studied in vinblastine-induced autophagocytosis. 2. The marker enzymes used were adenosine triphosphatase, lipase, inosine diphosphatase and thiamine pyrophosphatase. The following impregnation techniques were used: unbuffered osmium tetroxide impregnation, imidazole-buffered osmium tetroxide impregnation and uranyl-lead-copper impregnation. 3. Only a weak lipase activity was observed between the limiting membranes of a few AVs. The AV membranes were stained heavily with all impregnation techniques used. 4. The origin of AV membranes seems to be same in mouse liver and exocrine pancreas in vinblastine-induced autophagocytosis.

Filipin labelling and intramembrane particles on the membranes of early and later autophagic vacuoles in Ehrlich ascites cells

Cholesterol and intramembrane particle distribution on autophagic vacuole membranes was studied in Ehrlich ascites cells using filipin labelling and freeze-fracture electron microscopy. Unsaturated fatty acids were stained using imidazole-buffered osmium tetroxide. Autophagocytosis was induced with vinblastine, and early autophagic vacuoles were accumulated by lowering the ATP level in the cells with iodoacetate. Filipin labelling was observed in the limiting membranes of later, apparently hydrolase-containing autophagic vacuoles, whereas the most newly-formed, double-membrane limited vacuoles were not labelled. The limiting membranes of late, residual body-type vacuoles either showed patchy filipin-induced deformation or were completely smooth. Imidazole-buffered osmium tetroxide stained the membranes of newly-formed or developing autophagic vacuoles partly or entirely. The membranes of older vacuoles stained more weakly. Intramembrane particle density on the P-face of the outer limiting membranes of newly-formed autophagic vacuoles was similar to that on endoplasmic reticulum, and the density seemed to increase slightly later on. The size of the P-face particles increased when the vacuoles became older. The limiting membranes of late, residual body-type vacuoles were almost smooth. The inner limiting membranes and the membranes inside the autophagic were always almost particle-free. In conclusion, the amount of cholesterol, unsaturated fatty acids and protein in autophagic vacuole membranes changes during vacuole maturation.

Studies on vinblastine-induced autophagocytosis in mouse liver. V. A cytochemical study on the origin of membranes

The origin and the structure of the limiting membranes of autophagic vacuoles (AV) in mouse hepatocytes was studied using cytochemical techniques. Autophagocytosis was induced by an intraperitoneal injection of vinblastine (50 mg/kg). Imidazole-buffered osmium tetroxide impregnation was used as a marker for unsaturated fatty acids, and uranyl-lead-copper impregnation for the determination of possible connections of AV membranes with the other cellular membranes. AV membranes stained strongly with both techniques. The staining pattern of AV membranes differed from that of the other cellular membranes. AV's were frequently seen to fuse with vesicles containing very low density lipoprotein particles. No other connections of AV membranes with other cellular membranes were observed. The results suggest that if pre-existing cellular membranes are used in AV formation some kind of transformation must occur in these membranes during AV formation. The content of unsaturated fatty acids appears to be high in AV membranes.

Unbuffered osmium staining of cell organelles: alterations induced by cell injury

We have studied the localization of osmium reduction products to investigate the functional state of organelles as well as organelle interrelationships during cell injury. In normal hepatocytes osmium deposits of variable intensity are seen in nuclear envelope, endoplasmic reticulum. Golgi cisternae and vesicles and lysosomes. Buffering of osmium with s- collidine (pH 7.4) prevents the deposition of osmium. Reversible (30 min) and irreversible (60 min) ischemia without reflow causes no change in the pattern of osmium deposition. Irreversible ischemia followed by reflow causes decreased staining of endoplasmic reticulum (ER) and redistribution of the osmium deposits through the cytoplasm. Reversibly injured pancreatic acinar cells in cultured explants manifest a similar loss of osmium staining in the endoplasmic reticulum cisternae. The administration of antimicrotubule drugs induces an accentuation of osmium staining in localized cisternal elements of hepatocytes. These heavily stained cisternae appear to give rise to the bounding membranes of drug-induced autophagic vacuoles. Cytoplasmic organelles sequestered inside the autophagic vacuoles acquire intense staining when they begin to undergo degradation. In homogenized liver tissue all the subcellular organelles show osmium deposits. The deposits are preferentially localized along the organelle membranes. In particular the dense deposits in the ER lumen are not seen in the subcellular fractions. Phospholipase A2 (3 units/mg protein) enhances the deposition of osmium in the lumen of microsomal vesicles, whereas the presence of detergent has no such effect. Addition of EDTA to the homogenizing medium enhances the ultrastructural preservation of the subcellular fractions but has little effect on the deposition of osmium. OsO4 deposition occurs at acid pH and the intensity and pattern of the stain can be modified in vivo and in vitro. Osmium tetroxide deposition is induced at sites of membrane transformation (autophagic vacuoles) and degradation (lysosomes). Calcium influx and phospholipase activation (ischemia, tissue homogenization, phospholipase addition) enhance osmium deposition and/or influence the localization of the staining pattern.

Studies on vinblastine-induced autophagocytosis in mouse liver. II. Origin of membranes and acquisition of acid phosphatase

The origin of the membranes of autophagic vacuoles (AV) and acquisition of acid phosphatase into AV's were studied in vinblastine-induced autophagocytosis (VBL, 50 mg/kg, i.p.) in mouse hepatocytes. Using unbuffered OsO4, very intense staining was observed in the outer cisternae of the Golgi apparatus and also frequently in the cavity between the double membranes obviously destined to form AV's as well as in the cavity between the double membranes of newly formed AV's. There may occur a transformation process in the membranes limiting an AV analogous to that observed at the Golgi cisternae. The transformation of the outer AV membrane occurs independently of fusion with lysosomes. Inosine diphosphatase activity was localized within the cisternae and on the membranes of the endoplasmic recticulum and occasionally within the innermost cisterna of the Golgi apparatus. The results together with the unbuffered OsO4-staining pattern suggest that the membranes of most AV's are derived from the transformed smooth surfaced cisternae of the endoplasmic reticulum which do not have inosine diphosphatase activity. Acid phosphatase activity was localized in lysosomes, occasionally within the innermost cisternae of the Golgi apparatus, between the double membranes of a few newly formed AV's and within most older single membranes of a few newly formed AV's and within most older single membrane-limited AV's. VBL did not prevent the fusion of lysosomes with AV's.