Early events of secretory granule formation in the rat parotid acinar cell under the influence of isoproterenol. An ultrastructural and lectin cytochemical study

Abstract

The events involved in the maturation process of acinar secretory granules of rat parotid gland were investigated ultrastructurally and cytochemically by using a battery of four lectins [Triticum vulgaris agglutinin (WGA), Ulex europaeus agglutinin I (UEA-I), Glycine max agglutinin (SBA), Arachys hypogaea agglutinin (PNA)]. In order to facilitate the study, parotid glands were chronically stimulated with isoproterenol to induce secretion. Specimens were embedded in the Lowicryl K4M resin. The trans-Golgi network (TGN) derived secretory granules, which we refer to as immature secretory granules, were found to be intermediate structures in the biogenesis process of the secretory granules in the rat parotid acinar cell. These early structures do not seem to be the immediate precursor of the mature secretory granules: in fact, a subsequent interaction process between these early immature granule forms and TGN elements seems to occur, leading, finally, to the mature granules. These findings could explain the origin of the polymorphic subpopulations of the secretory granules in the normal acinar cells of the rat parotid gland. The lectin staining patterns were characteristic of each lectin. Immature and mature secretory gran- ules were labelled with WGA, SBA, PNA, and lightly with UEA-I. Cis and intermediate cisternae of the Golgi apparatus were labelled with WGA, and trans cisternae with WGA and SBA

An efficient two-step subcellular fractionation method for the enrichment of insulin granules from INS-1 cells

“…There are two main possible reasons for this. First, intracellular organelles are generally highly dynamic entities; this is precisely the case for iISGs and mISGs, the properties and protein contents of which continuously change during the granule maturation process, from budding at the TGN to release at the plasma membrane (D’Amico et al 2001 ). This may explain why our enriched fractions were contaminated by TGN contents.…”

Immunohistochemical and Immunocytochemical Localization of Amylase in Rat Parotid Glands and von Ebner's Glands by Ion Etching-Immunoscanning Electron Microscopy

“…The above-mentioned amylase distribution in the two types of SG in rat parotid acinar cells has been described in an immunoTEM study [36]. The peripheral ring structure of heterogeneous SG has been reported in parotid acinar cells of not only rat [1] but also mouse [25], insectivorous yellow bat [38], and cat [18, 23]. Conventional TEM observation indicated that the structure of serous SG is species-dependent [38].…”

“…Meanwhile, high amylase activity was detected in the parotid glands of guinea pig, rat, human, mouse, gerbil, rabbit, and insectivorous bat [15]. It is common knowledge that amylase is localized in the dark part of a TEM image of the parotid acinar SG of rat [1, 16, 36], gerbil [13, 14], and human [33], and conversely in the reflective light part on an SEM secondary electron image similar to the present study of the rat.…”