Chromaffin granules in the rat adrenal medulla release their secretory content in a particulate fashion

Abstract

Exocytosis is considered the main route of granule discharge in chromaffin cells. We recently provided ultrastructural evidence suggesting that piecemeal degranulation (PMD) occurs in mouse adrenal chromaffin cells. In the present study, we processed rat adrenal glands for transmission electron microscopy (TEM), and examined chromaffin cells for changes characteristic of PMD. Both adrenaline (A)-and noradrenaline (NA)-storing cells express ultrastructural features suggestive of a slow and particulate mode of granule discharge. In adrenaline-containing cells, some granules present enlarged dimensions accompanied by eroded or dissolved matrices. Likewise, a number of granules in NA-releasing cells show content reduction with variably expanded granule chambers. Dilated, empty granule containers are recognizable in the cytoplasm of both cell types. Characteristically, altered granules and empty containers are seen intermingled with normal, resting granules. In addition, chromaffin granules often show irregular profiles, with budding or tail-like projections of their limiting membranes. Thirty 150-nm-diameter membrane-bound vesicles with a moderately electron-dense or -lucent internal structure are observable in the cytoplasm of both cell types. These vesicles are seen among the granules and some of them are fused with the perigranule membranes in the process of attachment to or budding from the granules. These data add further support to the concept that PMD may be an alternative secretory pathway in adrenal chromaffin cells.

Altered secretory activity in rat adrenal chromaffin cells after experimentally induced bronchial asthma and dexamethasone treatment

“…However, the present study was in agreement with recent investigations [4][5][6] that provided further ultrastructural evidence for the hypothesis that these cells may express PMD as an alternative secretory pathway. Features of PMD manifested as budding, taillike projections, altered granules with eroded contents, dilated partially empty granules, and large completely empty containers were observed.…”

“…This implies that the limiting membranes of chromaffin granules adhere to and fuse with the plasma membrane of the chromaffin cell, and that the granule content is subsequently secreted into the extracellular space. Recent studies have provided ultrastructural evidence for an alternative route of granule discharge from adrenomedullary cells, called piecemeal degranulation (PMD) [4][5][6]. This consists of a particulate pattern of cell degranulation hitherto described in basophils, mast cells, and eosinophils [7][8][9].…”

Ultrastructural evidence of piecemeal degranulation in large dense-core vesicles of brain neurons

“…Hence a unifying concept including both LDCV and endocrine granules has been developed, and these structures are now often comprehensively referred to as large dense-core granules, irrespective of whether they are located in neurons or neuro-endocrine cells (Ho¨cker et al 1999;Kasai 1999;Koval et al 2001;Malosio et al 2004). Like LDCV, endocrine granules have been claimed to extrude their secretory content by exocytosis (Aunis 1998;Kasai 1999) but recently a particulate pattern of cell degranulation, called piecemeal degranulation (PMD), has been recognized in adrenal chromaffin cells and in endocrine cells of the gastro-intestinal epithelia (Crivellato et al 2002(Crivellato et al , 2003b(Crivellato et al , 2004(Crivellato et al , 2005). This secretory model implicates discrete and slow release of granule particles from storage granules without granule fusion with the plasma membrane and opening to the cell exterior (Dvorak 1991).…”

Immunohistochemical study of sustentacular cells in adrenal medulla of neonatal and adult rats using an antibody against S-100 protein

“…It has been postulated that the adrenal medullary sustentacular cells might regulate the calcium levels in the extracellular compartment [13]. It is proved that calcium ion participates in the mechanism of liberation of catecholamines, mainly noradrenaline [4]. It has been detected that the adrenal medullary sustentacular cells are mainly located and remarkably higher in the regions of the noradrenaline chromaffin cells than the regions of adrenaline chromaffin cells [21].…”