Role of aquaporins and regulation of secretory vesicle volume in cell secretion

Abstract

In exocrine glands, secretory proteins synthesized in the rough endoplasmic reticulum (RER) exhibit vectorial transport from ER through a succession of membrane-bounded components such as Golgi complex, condensing vacuoles and secretory granules. The secretory granules migrate to particular locations within the cell close to the apical membrane prior to the release of their contents into the acinar lumen. Currently, to release intragranular contents, secretory granules have been demonstrated to transiently dock and fuse at ‘porosome’, a permanent cup-shaped structures at the cell membranes. Then swelling of secretory granules occurs to allow explusion of intragranular contents. In this process, water and ion fluxes in the granule membrane appear to contribute to maintain secretory granule integrity and morphology via osmoregulation in secretory granules. Aquaporins (AQPs) are a family of small, hydrophobic, integral membrane proteins, which function as channels to permeate water and small solutes. The AQPs reside constitutively at the plasma membrane in most cell types. However, recent studies have demonstrated that the AQPs are present in secretory granules in exocrine glands, synaptic vesicles and intracellular vesicles in liver and kidney, implying that AQPs in secretory granules and vesicles are involved in their volume regulation. This paper reviews the possible role of AQPs on secretory granules, especially in exocrine glands, in secretory function.

Soybean protein fraction digested with neutral protease preparation, “Peptidase R”, produced by Rhizopus oryzae, stimulates innate cellular immune system in mouse

“…The proteins originating from Igh-4 and Aqp8 up-regulate phagocytosis and the migration of leukemia, respectively [26,27]. Elastases originating from Ela3 and Ela1 attach to microorganisms and foreign substances [28].…”

Immunohistological Study of the Major Salivary Glands in the Gray Short-Tailed Opossums (<i>Monodelphis domestica</i>)

“…AQPs represent constitutive elements of the plasma membrane in most secretory cell types of exocrine glands [19][20][21][22][23][24][25] . Recently, their presence has been demonstrated in secretory granules and vesicles, indicating an involvement in volume regulation of these structures 26) . In the salivary glands, AQP5 is probably involved in providing for an appropriate amount of fluid to be secreted 26,27) .…”

“…Recently, their presence has been demonstrated in secretory granules and vesicles, indicating an involvement in volume regulation of these structures 26) . In the salivary glands, AQP5 is probably involved in providing for an appropriate amount of fluid to be secreted 26,27) . In particular, in rat salivary glands, AQP5 is highly expressed in the apical plasma membrane of serous acinar cells, in the secretory canaliculi and in the intercalated duct cells.…”

Immunodetection of aquaporin 5 in sheep salivary glands related to pasture vegetative cycle

“…Recently, their presence has been demonstrated in secretory granules and vesicles, indicating an involvement in volume regulation of these structures [15]. Recent research on humans and laboratory mammals, aimed at identifying aquaporins and aquaglyceroporins in the digestive system, has demonstrated that AQP water channels are involved in the physiologic processes of digestion and absorption of the ingesta [16,17].…”

“…In the salivary glands, AQP5 is probably involved in providing for an appropriate amount of fluid to be secreted [15,30]. In particular, in rat salivary glands, AQP5 is highly expressed in the apical plasma membrane of serous acinar cells, in the secretory canaliculi and in the intercalated duct cells.…”