Pflugers Arch - Eur J Physiol (2003) 446:641–651 DOI 10.1007/s00424-003-1109-9 CELL AND MOLECULAR PHYSIOLOGY Tetsuya Akamatsu · Most Nahid Parvin · Kwartarini Murdiastuti · Chisato Kosugi-Tanaka · Chenjuan Yao · Osamu Miki · Norio Kanamori · Kazuo Hosoi Expression and localization of aquaporins, members of the water channel family, during development of the rat submandibular gland Received: 17 January 2003 / Accepted: 6 May 2003 / Published online: 28 June 2003  Springer-Verlag 2003 Abstract The expression and localization of aquaporins (AQP1–AQP5), members of the water channel family, in the developing rat submandibular gland were analysed using RT-PCR, Northern blotting and immunohistochem- istry to explore their relation to the development of this salivary gland. RT-PCR analysis revealed unique expres- sion patterns of each AQP. AQP1 was expressed consti- tutively during prenatal development, whereas the expression of AQP5 became more intense in the course of development from embryonic day 16.5 (E16) to E20. These expression patterns concurred with the results of Northern blot analysis. AQP3 and AQP4 mRNAs in the prenatal development were not detected in Northern blots, although they were detected by RT-PCR. During postna- tal development, AQP5 and AQP1 mRNAs were ex- pressed continuously, but no message for AQP3 or AQP4 was detected. AQP2 mRNA was not detected during either prenatal or postnatal development in this tissue. Immunohistochemical studies revealed that AQP5 was first localized at the apical membrane of proacinar cells at E18, and then became clearly distributed at the apical membrane of acinar cells in accordance with the differ- entiation and establishment of the mature acini. In addition, some vasculature also showed immunoreactivity for AQP5. AQP1 was immunolocalized in the blood vessels, including capillaries, of the gland throughout development. These observations suggest the existence of transcriptional regulation of rat AQP5, which is one of the most probable regulators of saliva production and secre- tion, during the establishment of the functional subman- dibular salivary gland. Keywords AQP5 · AQP1 · Submandibular gland · Acinar cell · Vasculature Introduction Aquaporins (AQPs) are transmembrane proteins that constitute a family of water channel molecules; they are generally responsible for rapid osmotic water movement across the plasma membrane in secretory and absorptive cells of many species of plants, bacteria, yeast, and mammals (for reviews, see [5, 41]). To date, 11 members have been identified in this channel family in mammals (for reviews, see [5, 13, 33]), and they are classified into 3 subgroups. AQP0, AQP1, AQP2, AQP4, AQP5 and AQP6 facilitate the transport of water only, whereas AQP3, AQP7, AQP9 and AQP10 allow the transport of glycerol and urea as well as water. For AQP10, a form with a shortened C-terminus has been identified also [10]. This AQP10 isoform facilitates the transport of neither urea nor glycerol and its water permeability is low. The last member, AQP8, facilitates the transport of water, but does not transport glycerol and urea. AQP8, however, represents a third subgroup because it lacks several amino acids that are conserved within the AQP family and possesses a very short C-terminus. Among the above members of the water channel family, AQP5 was first identified in the salivary gland [35] and has been shown consistently to be localized at the apical membranes of the acinar cells in the subman- dibular and parotid glands of rats [27]. This water channel is translocated from intracellular vesicles to the plasma membrane in response to the elevation of intracellular T. Akamatsu · M. N. Parvin · K. Murdiastuti · C. Kosugi-Tanaka · C. Yao · O. Miki · N. Kanamori · K. Hosoi ( ) ) Department of Physiology and Oral Physiology, School of Dentistry, The University of Tokushima, 18-15, 3-chome, Kuramotocho, 770-8504 Tokushima, Japan e-mail: hosoi@dent.tokushima-u.ac.jp Tel.: +81-88-633-7323 Fax: +81-88-633-7324 K. Murdiastuti Department of Periodontology, Faculty of Dentistry, Gadjah Mada University, 55281 Yogyakarta, Indonesia