Immunolocalization of AQP-5 in rat parotid and submandibular salivary glands after stimulation or inhibition of secretion in vivo

Abstract

In vitro studies of cultured salivary gland cells and gland slices have indicated that there may be regulated translocation of aquaporin (AQP)-5 between the apical plasma membrane and intracellular compartments of the secretory cells. However, it remains unknown whether AQP-5 in salivary glands is subject to regulated trafficking in vivo. To examine this possibility, we have investigated the subcellular localization of AQP-5 in rat parotid and submandibular glands fixed in vivo under conditions of stimulated or inhibited salivary secretion. Immunofluorescence and immunoelectron microscopy was used to determine the subcellular distribution of AQP-5 in control conditions following the stimulation of secretion with pilocarpine (a muscarinic agonist) or epinephrine (an α-adrenoceptor agonist) or during inhibition of basal secretion with atropine (a muscarinic antagonist) or phentolamine (an α-adrenoceptor antagonist). Under control conditions, >90% of AQP-5 was associated with the apical plasma membrane of acinar and intercalated duct cells, with only rare gold particles associated with intracellular membrane domains. Pilocarpine treatment dramatically increased saliva production but had no discernible effect on AQP-5 distribution. However, the increased salivary secretion was associated with luminal dilation and the appearance of a markedly punctate AQP-5 labeling pattern due to clustering of AQP-5 at the microvilli (especially evident in the parotid gland) after 10 min of drug injection. No changes in the subcellular localization of AQP-5 were seen in response to epinephrine, atropine, or phentolamine treatment compared with control tissues. Thus AQP-5 is localized predominantly in the apical plasma membrane under control conditions, and neither the onset nor the cessation of secretion is associated in vivo with any significant short-term translocation of AQP-5 between intracellular structures and the apical plasma membrane.

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

“…The positive immunoreactivity, likely localized at the level of intercellular canaliculi that radiate from the luminal space of the serous acini of the parotid and mandibular glands, indicates that the presence of AQP5 might increase the functionality of this small apical surface area. As for the parotid gland, the data also agrees with recent findings [13,44] indicating the role of AQP5 in the secretive process at apical membrane level in human parotid acinar cells.…”

“…On the other hand, it is lacking in mucous acinar cells and in striated ducts, indicating its important role in saliva production [14], further supported by the observation of markedly depressed rates of salivary secretion in APQ5-deficient mice [31]. The significance of AQP5 to human diseases may include important disorders of the lung, airways, sweat glands, lacrimal glands and the salivary glands [13,31,32]. A defective trafficking of AQP5 has been found in salivary gland biopsies of some patients with Sjögren's syndrome [33] where an abnormal distribution of AQP5 in salivary gland acini is likely to contribute to the deficiency of fluid secretion.…”

“…Samples were immediately fixed by immersion either in Carnoy's fluid followed by a post-fixation with calcium acetate 2%-paraformaldehyde 4% [36] or in paraformaldehyde 4% [13], dehydrated in a graded series of ethanol, cleared in xylene and embedded in paraffin wax. Both fixatives were freshly prepared every time.…”

“…AQPs represent constitutive elements of the plasma membrane in most secretory cell types of exocrine glands [8][9][10][11][12][13][14]. Recently, their presence has been demonstrated in secretory granules and vesicles, indicating an involvement in volume regulation of these structures [15].…”

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

“…CK19 was also detected the cytoplasm of ductal cells. 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) .…”