Immunolocalization of AQP-5 in rat parotid and submandibular salivary glands after stimulation or inhibition of secretion in vivo
American Journal of Physiology - Gastrointestinal and Liver Physiology
In vitro studies of cultured salivary gland cells and gland slices have indicated that there may be regulated translocation of AQP5 between the apical plasma membrane and intracellular compartments of the secretory cells. However it remains unknown whether AQP5 in salivary glands is subject to regulated trafficking in vivo. In order to examine this possibility, we have investigated the subcellular localization of AQP5 in rat parotid and submandibular glands fixed in vivo under conditions of
... r conditions of stimulated or inhibited salivary secretion. Immunofluorescence and immunoelectron microscopy was used to determine the subcellular distribution of AQP5 in control conditions, following the stimulation of secretion with pilocarpine (a muscarinic agonist) or epinephrine (an -adrenoceptor agonist) or during inhibition of basal secretion with atropine (a muscarinic antagonist) or phentolamine (an -adrenoceptor antagonist). Under control conditions, > 90% of AQP5 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 AQP5 distribution. However, the increased salivary secretion was associated with luminal dilation and the appearance of a markedly punctate AQP5 labeling pattern due to clustering of AQP5 at the microvilli (especially evident in the parotid gland) after 10 min of drug injection. No changes in the subcellular localization of AQP5 were seen in response to epinephrine, atropine or phentolamine treatment as compared to control tissues. Thus AQP5 is predominantly localized 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 AQP5 between intracellular structures and the apical plasma membrane.