title: Use of tannic acid to study cytoplasmic vesicles and membrane invaginations in epididymal fat pads of ageing mice.
abstract: A staining technique based upon the known ability of tannic acid to selectively stain the outer layer of the triple-layered plasma membrane was used, along with electron microscopic examination of stained, serial sections, to differentiate between surface invaginations, clusters of invaginations, free vesicles and tubular channels in epididymal fat pads from young, fed and fasted mice and from old, fed mice. A preliminary semiquantitative evaluation of the average number of each type of structure per cell was attempted. There were no significant numbers of free cytoplasmic vesicles of approximately 50 nm diameter (the dimension of most surface invaginations) under any conditions studied. Most apparent vesicles were stained by tannic acid and were, therefore, actually invaginations of the plasma membrane. There were no tubular channels of this size seen in any of the electron micrographs examined in serial sections. We estimated that there are about 50 single invaginations per micron2 of plasma membrane surface in both young and old fed mice. In addition there were about 20 invaginations/micron2 grouped as clusters of 2-15 per group (mean, 4 per group) in the fed mice. There was a tendency for the number of invaginations in clusters to increase during fasting; about 40% of the surface invaginations were grouped in clusters in adipocytes of fasted mice. Although there was no effect of ageing on the concentrations of surface invaginations or in their groupings as clusters, the total number of invaginations per cell must have increased almost 3-fold as the cells enlarged. The function of these surface invaginations and deeply penetrating groups of invaginations remains to be elucidated.
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology*; D000375:Aging; D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure*; D003593:Cytoplasm / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000648:ultrastructure*; D004822:Epididymis / Q000033:anatomy & histology; D005215:Fasting; D047348:Hydrolyzable Tannins; D050356:Lipid Metabolism; D008066:Lipolysis; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D008870:Microtubules / Q000648:ultrastructure; D013634:Tannins; D014617:Vacuoles / Q000648:ultrastructure
chemical_list: D047348:Hydrolyzable Tannins; D013634:Tannins