Electroneutral cation-Cl- cotransporters NKCC2β and NCCβ expressed in the intestinal tract of Japanese eel Anguilla japonica

In the present study, we aimed to elucidate the mechanisms of intestinal Na+ and Cl- absorption in Japanese eel, focusing on electroneutral cation-Cl- cotransporters, NKCC2 beta and NCC beta, expressed in the intestinal tract. First, we cloned cDNAs encoding NKCC2 beta and NCC beta from the intestinal tract of Japanese eel. In both freshwater- and seawater-acclimated eels, quantitative PCR analysis showed that NKCC2 beta was predominantly expressed in the anterior and posterior intestines, and that NCC beta expression was specifically high in the rectum. According to immunohistochemistry with anti-eel NKCC2 beta (reacting with NKCC2 beta but not with NCC beta) and T4 antibody (reacting with both NKCC2 beta and Nap), NKCC2 beta was localized in the apical surface of the epithelial cells in the anterior and posterior intestines, whereas NCC beta was likely to be distributed to that in the rectum. Furthermore, a specific NCC inhibitor, hydrochlorothiazide, inhibited of Na+ and Cl- absorption, as well as water absorption, in the rectal sac preparations from seawater eel, indicating the involvement of NCC beta in ion absorption in the rectum. Our findings indicate that NKCC2 beta expressed in the anterior and posterior intestines and NCC beta in the rectum are importantly involved in ion absorption to reduce osmolality of ingested seawater prior to water absorption in seawater-acclimated eel. (C) 2011 Elsevier Inc. All rights reserved.