title: Effects of isoproterenol on aquaporin 5 levels in the parotid gland of mice in vivo.
abstract: In the membrane fraction of mouse parotid gland (PG), the protein level of aquaporin 5 (AQP5), a member of the water channel family, was increased by injection (ip) of isoproterenol (IPR), a β-adrenergic agonist, at 1 h, and stayed at high levels until 6 h; this change occurred simultaneously as amylase secretion. The AQP5 level then decreased and returned toward the original level at 12-48 h. After IPR injection, the AQP5 mRNA gradually increased and reached a maximum at 24 h. The facts suggest a rapid appearance of AQP5 at plasma membrane by IPR and subsequent degradation/metabolism by activation of proteolytic systems. Pretreatment of animals with two calpain inhibitors, N-Ac-Leu-Leu-methininal (ALLM) and calpeptin, as well as a protein synthesis inhibitor, cycloheximide (CHX), significantly suppressed the IPR-induced AQP5 degradation in the PG membrane fraction; such suppression was not observed by two proteasome inhibitors, MG132 and lactacystin, or the lysosome denaturant chloroquine, although most of these inhibitors increased AQP5 protein levels in unstimulated mice. The AQP5 protein was also degraded by μ-calpain in vitro. Furthermore, we demonstrated that μ-calpain was colocalized with AQP5 in the acinar cells by immunohistochemistry, and its activity in the PG was increased at 6 h after IPR injection. These results suggest that the calpain system was responsible for IPR-induced AQP5 degradation in the parotid gland and that such a system was coupled to the secretory-restoration cycle of amylase in the PG.
authors.affiliation: Department of Molecular Oral Physiology, Institute of Health Biosciences, University of Tokushima Graduate School, Tokushima-Shi, Tokushima, Japan; and.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.forename: Chenjuan
authors.initials: C
authors.lastname: Yao
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Akamatsu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yoshimura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Hosoi
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000681:Amylases / Q000032:analysis / Q000378:metabolism; D000818:Animals; D051402:Aquaporin 5 / Q000032:analysis* / Q000378:metabolism; D002154:Calpain / Q000032:analysis / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D007150:Immunohistochemistry; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010306:Parotid Gland / Q000737:chemistry* / Q000187:drug effects / Q000201:enzymology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology
chemical_list: D000318:Adrenergic beta-Agonists; D051402:Aquaporin 5; D011500:Protein Synthesis Inhibitors; D000681:Amylases; D002154:Calpain; C449002:mu-calpain; D007545:Isoproterenol
keywords: aquaporin 5; exocytosis; isoproterenol; parotid gland; μ-calpain