Labilit� structurale des granules de s�cr�tion contenant du zinc des cellules ? du pancr�as apr�s gazage avec de l'hydrog�ne sulfur�

Abstract

Summary. Treatment of vertebrate pancreatic islet tissue with hydrogen sulphide, thus initiating the sulphidesilver procedure for ultrastructural visualization of heavy metals in tissues, evoked marked swelling in zinc-containing secretion granules of fl-cells in several species rapidly leading to disruption of many granules. Other organelles of the fi-cells were unaffected, as also were the secretion gramfles of adjacent zinc-containing ~2-cells. Likewise, fiand ~2-granules with no heavy metals or only traces of them, like those of the guinea pig and the coypu, were all well preserved after gassing with hydrogen sulphide. It is suggested that this observation may give some information on insulin-zinc-sulphydryl relationships in vivo. Labilitg structurale des granules de sdcrgtion contenant du zinc des cellules fl du pancrgas aprgs gazage avec de l'hydrog~ne sulfurdRdsumd. Le traitement des ilots pancr6atiques de plusieurs espgces de vert6br6s avec de l'hydrog~ne sulfur6, eonstituant ainsi la phase initiale de la mgthode sulfureargent pour la visualisation ultrastructurale des m6taux lourds darts les tissus, provoquait un gonflement marqu6 des granules de s6crgtion zineif~res des cellules fl dans plusieurs esp~ees, conduisanb rapidement ~ la rupture de beaueoup de granules. D'autres organelles des cellules fl restaient intacts, ainsi que les granules de s6cr6tion des cellules e2 zincif~res voisines. De m6me, les granules fl et ~ sans ou avec seulement des traces de m6taux lourds, eomme ceux du cobaye et du nutria, 6taient bien conserv6s apr~s le gazage avec l'hydrog6ne sulfur6. --On sugg~re que cette observation peut donner quelques aspects sur les relations insuline-zinc-sulfhydryl in vivo. Strulcturelle Labilitgit yon Selcretionsgranula mit Zinlcgehalt in panl~reatischen B-Zellen naeh Begasung mit SehwefelwasserstoffZusammenfassung. Behandlung mehrerer Arten von pankreatischem Inselgewebe yon Wirbeltieren mit Sehwefelwasserstoff, womit die Sulfid-Silber-Methode zur ultrastrukturellen Darstellung yon Gewebe-Schwermetallen eingeleitet wird, verursacht eine ausgesprochene Anschwellung der zinkhaltigen Sekretionsgranula der flZellen, die schnell zum ZerfM1 der Granula fiihrt. Andere Zellorganellen der fl-Zellen waren nicht besch~digt, auch nicht die Sekretionsgranula der benachbarten ~-Zellen. Ebenfalls waren fl-und ~-Granula mit keinen oder nur Spuren yon Schwermetallen, wie die des Meerschweinchens und der Nutria, alle wohlbehalten nach der Behandlung mit Sehwefelwasserstoff. --Als eine Arbeitshypothese fiir zukiinftige Untersuchungen wird angedeutet, dal3 diese Beobachtung yon Bedeutung in Bezug auf die InsulinZink-Sulfhydryl-Verh~ltnisse sein kann.

Zinc transporters and their role in the pancreatic β‐cell

“…Besides a more compact packaging of insulin in the secretory granules, zinc‐insulin crystallization is also believed to protect insulin against proteolytic degradation 58,59 . However, several data argue against this idea: (i) the presence of an intact 5808 Da insulin peptide as one sharp mass peak in the spectrum of islets of both wild‐type and ZnT8 −/− mice, measured by in situ peptidomics 26 ; and (ii) the non‐crystallized guinea pig and coypu insulin would be more vulnerable to degradation, compared with human crystallized insulin 60,61 .…”

The Zn2+-transporting Pathways in Pancreatic β-Cells

“…The precise subcellular localization and distribution of Zn 2ϩ in islets is also under debate. Histological data in fixed cells have shown mainly granular localization of Zn 2ϩ (27,28), whereas experiments with fractionation of islets have demonstrated that only 20 -30% of the total islet Zn 2ϩ was associated with the granular fraction (26,29). Given the significance of Zn 2ϩ for proinsulin biosynthesis and exocytosis, understanding the mechanisms of its uptake into islet cells is important.…”

65Zinc and Endogenous Zinc Content and Distribution in Islets in Relationship to Insulin Content*

“…2 and total zinc contents shown in Table 1 that granular zinc (~30% of the islet zinc) under all culture conditions was sufficient to account for the 2-zinc-insulin hexamer as a storage form of granular insulin. 2 The possibility that ZINC, RELATIONSHIP TO INSULIN CONTENT OF ISLETS 881 complexes with a lower zinc to insulin ratio may exist in the rat /3 cell should not be excluded, particularly when considering the hazards of relating too closely quantification of zinc by atomic absorption with that of rat insulin by RIA. However, complexes with much higher zinc to insulin ratios, which can be produced in vitro (23), are not likely to exist in vivo because of the limited zinc content of the granule compartment.…”

“…Results show that 1) zinc exists in a metabolically labile islet compartment(s) as well as in secretory granules; and 2) extragranular zinc, although not directly associated with insulin storage, may act as a reservoir for granular zinc and may regulate insulin synthesis, storage, and secretion in ways as yet unknown. (Endocrinology 115: [877][878][879][880][881]1984) E ARLY histological data suggested that 0-cell zinc is exclusively localized in the protein-insulin core of the secretory vesicle (1)(2)(3)(4). However, standard fixing and staining techniques may have removed less tightly bound zinc from either the granular or extragranular compartments (5).…”