title: Subcellular distribution of urea transporter in the collecting tubule of shark kidney is dependent on environmental salinity.
abstract: In the kidney of marine elasmobranchs, urea reabsorption from filtered urine is essential for maintaining high levels of urea in the body. In the kidney of the houndshark, Triakis scyllium, we previously found that a facilitative urea transporter (UT) is localized to a specific nephron segment, the collecting tubule, suggesting that the collecting tubule has an important role in the urea reabsorption process. To elucidate the roles of UT, we transferred T. scyllium to high (130%) and low (30%) salinity, and examined UT mRNA levels and UT distribution patterns in the kidney using real-time PCR and semi-quantitative fluorescence immunohistochemistry, respectively. Following transfer to low and high salinity, houndshark decreased and increased plasma urea concentrations, respectively, in order to control plasma osmolality. The abundance of UT mRNA did not differ among the experimental groups, whereas that of UT protein in the collecting tubule was significantly decreased in 30% seawater (SW). Furthermore, the subcellular UT distribution was dramatically changed. UT in the apical plasma membrane of collecting tubule almost disappeared in 30% SW, whereas it slightly increased in 130% SW compared with 100% SW. Conversely, reverse transfer of fish from 30 to100% SW restored UT in the apical membrane. These results indicate that the accumulation of UT to the apical plasma membrane of the collecting tubule of Triakis is an important factor for regulating urea reabsorption in the kidney.
authors.affiliation: Laboratory of Physiology, Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan. proton@ori.u-tokyo.ac.jp
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Shin
authors.initials: S
authors.lastname: Takaki
authors.forename: Susumu
authors.initials: S
authors.lastname: Hyodo
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004777:Environment; D015870:Gene Expression / Q000187:drug effects; D007124:Immunoenzyme Techniques; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000378:metabolism; D054712:Salinity; D012754:Sharks / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D000096982:Urea Transporters
chemical_list: D026901:Membrane Transport Proteins; D012333:RNA, Messenger; D012965:Sodium Chloride; D000096982:Urea Transporters