title: Effects of repeated administration of pilocarpine and isoproterenol on aquaporin-5 expression in rat salivary glands.
abstract: Aquaporins are water channel proteins which enable rapid water movement across the plasma membrane. Aquaporin-5 (AQP5) is the major aquaporin and is expressed on the apical membrane of salivary gland acinar cells. We examined the effects of repeated administration of pilocarpine, a clinically useful stimulant for salivary fluid secretion, and isoproterenol (IPR), a stimulant for salivary protein secretion, on the abundance of AQP5 protein in rat salivary glands by immunofluorescence microscopy and semi-quantitative immunoblotting. Unexpectedly AQP5 was decreased in pilocarpine-administered salivary glands, in which fluid secretion must be highly stimulated, implying that AQP5 might not be required for fluid secretion at least in pilocarpine-administered state. The abundance of AQP5, on the other hand, was found to be significantly increased in IPR-administered submandibular and parotid glands. To address the possible mechanism of the elevation of AQP5 abundance in IPR-administered animals, changes of AQP5 level in fasting animals, in which the exocytotic events are reduced, were examined. AQP5 was found to be decreased in fasting animals as expected. These results suggested that the elevation of cAMP and/or frequent exocytotic events could increase AQP5 protein. AQP5 expression seems to be easily changed by salivary stimulants, although these changes do not always reflect the ability in salivary fluid secretion.
authors.affiliation: Department of Stomatology and Maxillofacial Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma ; Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Taketo
authors.initials: T
authors.lastname: Susa
authors.affiliation: Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sawai
authors.affiliation: Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Aoki
authors.affiliation: Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Iizuka-Kogo
authors.affiliation: Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kogo
authors.affiliation: Department of Stomatology and Maxillofacial Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma.
authors.forename: Akihide
authors.initials: A
authors.lastname: Negishi
authors.affiliation: Department of Stomatology and Maxillofacial Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yokoo
authors.affiliation: Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Takata
authors.affiliation: Department of Anatomy and Cell Biology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsuzaki
keywords: aquaporin-5 (AQP5); isoproterenol; pilocarpine; repeated administration; salivary gland