Regulation of the Cl-/HCO3- exchanger AE2 in rat thick ascending limb of Henle's loop in response to changes in acid-base and sodium balance

The Cl-/HCO3- exchanger AE2 is believed to be involved in transcellular bicarbonate reabsorption that occurs in the thick ascending limb of Henle's loop (TAL). The purpose of this study was to test whether chronic changes in acid-base status and sodium intake regulate AE2 polypeptide abundance in the TAL of the rat. Rats were subjected to 6 d of loading with NaCl, NH4Cl, NaHCO3, KCl, or KHCO3. AE2 protein abundance was estimated by semiquantitative immunoblotting in renal membrane fractions isolated from the cortex and the outer medulla of treated and control rats. In the renal cortex, AE2 abundance was markedly increased in response to oral loading with NH4Cl or with NaCl. In contrast, AE2 abundance was unchanged in response to loading with KCl or with NaHCO3 and was decreased by loading with KHCO3. The response of AE2 in the outer medulla differed from that in the cortex in that HCO3 loading increased AE2 abundance when administered with Na+ but had no effect when administered with K+. Immunohistochemistry revealed that NaCl loading increased AE2 abundance in the basolateral membrane of both the cortical and the medullary TAL. In contrast, NH4Cl loading increased AE2 abundance only in the cortical TAL but not in the medullary TAL. These results suggest that regulation of the basolateral Cl-/HCO3- exchanger AE2 plays an important role in the adaptation of bicarbonate absorption in the TAL during chronic acid-base disturbances and high sodium intake. The present study also emphasizes the contribution of cortical TAL adaptation in the renal regulation of acid-base status.