The detailed localization pattern of Na+/K+/2Cl- cotransporter type 2 and its related ion transport system in the rat endolymphatic sac.
The endolymphatic sac (ES) is a part of the membranous labyrinth. ES is believed to perform endolymph absorption, which is dependent on several ion transporters, including Na(+)/K(+)/2Cl(-) cotransporter type 2 (NKCC-2) and Na(+)/K(+)-ATPase. NKCC-2 is typically recognized as a kidney-specific ion transporter expressed in the apical membrane of the absorptive epithelium. NKCC-2 expression has been confirmed only in the rat and human ES other than the kidney, but the detailed localization features of NKCC-2 have not been investigated in the ES. Thus, we evaluated the specific site expressing NKCC-2 by immunohistochemical assessment. NKCC-2 expression was most frequently seen in the intermediate portion of the ES, where NKCC-2 is believed to play an important role in endolymph absorption. In addition, NKCC-2 expression was also observed on the apical membranes of ES epithelial cells, and Na(+)/K(+)-ATPase coexpression was observed on the basolateral membranes of ES epithelial cells. These results suggest that NKCC-2 performs an important role in endolymph absorption and that NKCC-2 in apical membranes and Na(+)/K(+)-ATPase in basolateral membranes work coordinately in the ES in a manner similar to that in renal tubules.
Akiyama
Kosuke
K
Dept. of Otolaryngology, Faculty of Medicine, Kagawa University, Kita-gun, Kagawa, Japan. kakaka@med.kagawa-u.ac.jp
Miyashita
Takenori
T
Matsubara
Ai
A
Mori
Nozomu
N
D000818:Animals; D004712:Endolymphatic Sac / Q000648:ultrastructure*; D007150:Immunohistochemistry; D017136:Ion Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters / Q000032:analysis*; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D064466:Solute Carrier Family 12, Member 1
C578714:SLC12A1 protein, human; C578716:Slc12a1 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D000254:Sodium-Potassium-Exchanging ATPase
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