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Aquaporin-8 (AQP-8)


Distribution and roles of aquaporins in salivary glands.

Salivary glands are involved in secretion of saliva, which is known to participate in the protection and hydratation of mucosal structures within the oral cavity, oropharynx and oesophagus, the initiation of digestion, some antimicrobial defence, and the protection from chemical and mechanical stress. Saliva secretion is a watery fluid containing electrolytes and a mixture of proteins and can be stimulated by muscarinic and adrenergic agonists. Since water movement is involved in saliva secretion, the expression, localization and function of aquaporins (AQPs) have been studied in salivary glands. This review will focus on the expression, localization and functional roles of the AQPs identified in salivary glands. The presence of AQP1, AQP5 and AQP8 has been generally accepted by many, while the presence of AQP3, AQP4, AQP6 and AQP7 still remains controversial. Functionally, AQP5 seems to be the only AQP thus far to be clearly playing a major role in the salivary secretion process. Modifications in AQPs expression and/or distribution have been reported in xerostomic conditions.

MeSH Terms

  • Aging
  • Animals
  • Aquaporin 5
  • Aquaporins
  • Biological Transport, Active
  • Cell Line
  • Diabetes Mellitus
  • Head and Neck Neoplasms
  • Humans
  • Protein Transport
  • Salivary Glands
  • Sjogren's Syndrome
  • Water
  • Xerostomia

Expression of aquaporins 7 and 8 in the developing rat testis.

Aquaporin (AQP) is a molecule that facilitates water permeability through cell membranes and is widely distributed in the mammalian body. Among members of the AQP family, AQP7 and AQP8 are predominantly expressed in the testis. This paper examined the expression of these two AQPs in the developing rat testis, using northern blot and immunohistochemistry to visualize their roles during the progression of spermatogenesis in the developing testis. In adult rats, expression of AQP7 was localized to spermatids, whereas AQP8 protein was observed in spermatocytes. In the developing testis, transcripts of AQP7 became detectable between 23 and 25 days post-partum, when round spermatids have been reported to appear. On the other hand, AQP8 mRNA was first detected between 13 and 16 days post-partum, consistent with the reported first appearance of spermatocytes (13-14 days). AQP7 and AQP8 proteins were detectable at 28 days post-partum. The results suggest that AQP7 and AQP8 appear in the testis in accordance with the maturation of germ cells, and are involved in spermatogenesis.

MeSH Terms

  • Aging
  • Animals
  • Aquaporins
  • Blotting, Northern
  • Gene Expression
  • Immunohistochemistry
  • Ion Channels
  • Male
  • RNA, Messenger
  • Rats
  • Rats, Sprague-Dawley
  • Spermatids
  • Spermatocytes
  • Spermatogenesis
  • Testis