Kidney-specific chloride channel, OmClC-K, predominantly expressed in the diluting segment of freshwater-adapted tilapia kidney.
The kidney plays an important role in osmoregulation in freshwater teleosts, which are exposed to the danger of osmotic loss of Na(+) and Cl(-). However, ion-transport mechanisms in the kidney are poorly understood, and ion transporters of the fish nephron have not been identified thus far. From Mozambique tilapia, Oreochromis mossambicus, we have cloned a chloride channel, which is a homologue of the mammalian kidney-specific chloride channel, ClC-K. The cDNA of the channel, named OmClC-K, encodes a protein whose amino acid sequence has high homology to Xenopus and mammalian ClC-K (Xenopus ClC-K, 41.8%; rat ClC-K2, 40.9%; rat ClC-K1, 40.1%). The mRNA of OmClC-K was expressed exclusively in the kidney, and the expression level of mRNA was increased more in freshwater-adapted fish than seawater-adapted fish. The immunohistochemical study using a specific antibody showed that OmClC-K-positive cells were specifically located in the distal nephron segments. Immunoelectron microscopy further showed that immunoreaction of OmClC-K was recognizable on the structure of basolateral membrane infoldings in the distal tubule cells. The localization of OmClC-K and its induction in hypoosmotic media suggest that OmClC-K is involved in Cl(-) reabsorption in the distal tubule of freshwater-adapted tilapia.
Miyazaki
Hiroaki
H
Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Japan. hmiyazak@ori.u-tokyo.ac.jp
Kaneko
Toyoji
T
Uchida
Shinichi
S
Sasaki
Sei
S
Takei
Yoshio
Y
D000222:Adaptation, Physiological / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D027321:Anion Transport Proteins; D001834:Body Water; D016764:Cell Polarity; D018118:Chloride Channels / Q000096:biosynthesis* / Q000235:genetics; D002712:Chlorides / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D005618:Fresh Water; D005786:Gene Expression Regulation; D007038:Hypotonic Solutions / Q000494:pharmacology; D017136:Ion Transport; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D008565:Membrane Proteins; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009865:Oocytes; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012623:Seawater; D013045:Species Specificity; D017210:Tilapia / Q000235:genetics* / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000235:genetics*; D029867:Xenopus Proteins; D014982:Xenopus laevis
D027321:Anion Transport Proteins; C489932:CLCNKA protein, human; D018118:Chloride Channels; D002712:Chlorides; C486572:Clcnkb protein, rat; D018076:DNA, Complementary; D007038:Hypotonic Solutions; D008565:Membrane Proteins; D012333:RNA, Messenger; D029867:Xenopus Proteins; C489934:clcnka protein, Xenopus