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1 Departments of Pediatrics, Physiology and Nutritional Sciences, University of Arizona Health Sciences Center, Steele Memorial Children's Research Center, Tucson, AZ, USA
* To whom correspondence should be addressed. E-mail: fghishan{at}peds.arizona.edu.
Apically expressed intestinal and renal sodium-hydrogen exchangers (NHEs) play a major role in Na+ absorption. Our previous studies on NHE ontogeny have shown that NHE2 and NHE3 are expressed at very low levels in young animals. Furthermore, single and/or double NHE2 and NHE3 knockout mice display no obvious abnormalities before weaning. These observations suggest that other transporter(s) may be involved in intestinal Na+ absorption during early life. The current studies were designed to clone the novel rat intestinal NHE8 cDNA and to decipher the NHE8 protein localization and gene expression pattern during different developmental stages. The rat NHE8 cDNA has 2160 bp and encodes a 575 AA protein. An antibody against NHE8 protein was developed. Immunohistochemistry staining indicated apical localization of NHE8 protein in rat intestinal epithelial cells. The apical localization of NHE8 was also confirmed by its presence in brush-border membrane and its absence in basolateral membrane preparations. Northern blotting utilizing a NHE8 specific probe demonstrated higher NHE8 mRNA expression in young animals in comparison to adult animals. Western blot analysis revealed a similar pattern. Tissue distribution with multiple human tissue RNA blot showed that NHE8 was expressed in multiple tissues including the gastrointestinal tract. In conclusion, we have cloned the full-length NHE8 cDNA from rat intestine and further showed its apical localization in intestinal epithelial cells. We have also shown that NHE8 gene expression and protein expression were regulated during ontogeny. Our data suggests that NHE8 may play an important role in intestinal Na+ absorption during early life.
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