title: Abnormal subcellular localization of AQP5 and downregulated AQP5 protein in parotid glands of streptozotocin-induced diabetic rats.
abstract: BACKGROUND
  The mechanisms underlying diabetic xerostomia have not been clarified in relation with aquaporin-5 (AQP5) subcellular localization in salivary glands.
  
  
  METHODS
  Western blotting, real-time PCR, and immunocytochemistry were used to analyse AQP5 protein levels and mRNA expression. AQP5 protein levels were measured in the apical plasma membrane (APM) and detergent-insoluble fraction prepared from streptozotocin-diabetic rat parotid glands.
  
  
  RESULTS
  Despite an increase in AQP5 mRNA, AQP5 protein levels were decreased in diabetic parotid glands compared with controls. Immunohistochemical studies indicated that AQP5, under unstimulated conditions, colocalised with flotillin-2 and GM1 with a diffuse pattern in the apical cytoplasm of acinar and duct cells in both control and diabetic rats. Ten minutes after intravenous injection of muscarinic agonist cevimeline, AQP5 was dramatically increased together with flotillin-2 and GM1 in the APM of parotid acinar and duct cells of control but not diabetic rats. Sixty minutes after injection, AQP5 was located in a diffuse pattern in the apical cytoplasm in both rats. Treatment of the parotid tissues with cevimeline for 10min increased the Triton X-100 solubility of AQP5 in control but not diabetic rats. Administration of insulin to diabetic rats tended to restore the cevimeline-induced translocation of AQP5.
  
  
  CONCLUSIONS
  Lack of AQP5 translocation in the salivary gland in response to a muscarinic agonist and downregulation of AQP5 protein might lead to diabetic xerostomia.
  
  
  CONCLUSIONS
  Cevimeline is useful to cure diabetic xerostomia under insulin administration.
authors.affiliation: Department of Medical Pharmacology, The University of Tokushima Graduate School, Tokushima 770-8504, Japan.
authors.forename: Di
authors.initials: D
authors.lastname: Wang
authors.forename: Zhenfang
authors.initials: Z
authors.lastname: Yuan
authors.forename: Noriko
authors.initials: N
authors.lastname: Inoue
authors.forename: Gota
authors.initials: G
authors.lastname: Cho
authors.forename: Masayuki
authors.initials: M
authors.lastname: Shono
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ishikawa
mesh_terms: D000818:Animals; D051402:Aquaporin 5 / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007150:Immunohistochemistry; D007328:Insulin / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D018721:Muscarinic Agonists / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D010306:Parotid Gland / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D011812:Quinuclidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013876:Thiophenes / Q000494:pharmacology; D013997:Time Factors; D014987:Xerostomia / Q000235:genetics / Q000378:metabolism
chemical_list: D051402:Aquaporin 5; D007004:Hypoglycemic Agents; D007328:Insulin; D008565:Membrane Proteins; D018721:Muscarinic Agonists; D011812:Quinuclidines; D013876:Thiophenes; C106354:flotillins; D009569:Nitric Oxide; D006152:Cyclic GMP; C059240:cevimeline