Fusion and discharge of rat submandibular gland acinar secretory granules captured by quick freezing.

Abstract

Abstract:This study was carried out to observe morphologically and quantitatively the membrane fusion of secretory granules and exocytotic figures during secretion while keeping alive the submandibular gland acinar secretory granules of male rats . The results showed that in comparison with the secretory granules of stimulated and control rats by quick freezing with OsO4. acetone and paraformaldehyde•acetone, (a) secretory granules apposed and fused with each other in a convex and concave form, and filamentous structure (90-100 A) and actin-like filaments (40 A) were intercalated between the two closely apposed granules, (b) part of the two fused outer leaflets of the granule disappeared in the initial stages of the two fused granule membrane and a fused, double thickness lipid bilayer was observed. After the contents of one granule were poured into the other fused granule, association of the two fused membranes was observed; and (c) appearance of a convex shaped granule membrane facing toward the plasma membrane and depression of the plasma membrane facing the cytoplasm represented the initial stage of exocytosis. On the other hand, filamentous structures intercalated between the plasma membrane and the granule membrane were detected. Lastly, (d) the width of the tubular structures in the control groups was narrower than that in the stimulated gland at discharge after the fusion of the two membranes.From these results it was concluded that the concave and convex form in the granule membrane fusion and the association of plasmalemma-granules with tubular structures in the exocytosis may be intrinsic phenomena of the double lipid bilayer in secretory granule fusion, thus confirming the exclusion of intramembranous particles.

Serous Cells in the Parotid Glands of Two Species of Tamarins: Polarized Secretory Granules

“…All of the foregoing examples of granule pseudopodia were observed by conventional transmission electron microscopy. Odajima and Nakane (1984) noted the same phenomenon in quick-frozen rat submandibular acinar cells, as did Tanaka (1980) in freeze-fractured pancreatic acinar cells. Granule contents are expelled via these extensions, leaving behind invaginations of the luminal membrane that are shaped like Florence flasks.…”

Ultrastructure of the parotid salivary glands in seven species of fruit bats in the genus Artibeus

“…Granules connected by a process usually have only a single membrane between the two moieties rather than two appressed membranes. Such a configuration is more in keeping with a fusion process (Tandler and Poulsen, 1976;Neutra and Schaeffer, 1977;Vidić, 1977;Tanaka, 1982;Shimono et al, 1984, Odajima andNakane, 1984) than with internalization of limiting membranes of granules. We recently described mucous droplets in the accessory submandibular glands of long-winged bats (Miniopterus schreibersi and M. magnator) that were delimited by multiple membranes (Tandler et al, 1994); it was posited that these supernumerary membranes originated by the simple expedient of Golgi saccules wrapping themselves around the nascent droplets.…”

Ultrastructure of the submandibular gland in the African multimammate rodent, Praomys natalensis

“…The acinar cells, shown to be seromucous in nature by histochemistry (Sirigu et al, 1985), contain secretory granules with a n unusual substructure. Unlike mouse and rat submandibular gland granules, which, when adequately preserved, have skeins or hoops of moderately-dense ropy material in a light matrix (Ciofi Luzzatto et al, 1968;Martinez-Hernandez et al, 1972;Alvares and Sesso, 1975;Odajima and Nakane, 1984), typical Praomys granules have a targetlike inclusion in a quite dense matrix. Of the rodents that have had their submandibular glands examined by electron microscopy, only the Japanese wood mouse, Apodemus ainu ainu, has acinar secretory granules that bear some resemblance to those of Praomys (Odajima, 1981).…”