Expression and localization of two isoforms of AQP10 in human small intestine

Background information. AQP10 (aquaporin 10) is a new member of water channels and two different transcripts have been reported. The difference between these transcripts is in the presence or the absence of an insertion of 475 nt, which leads to a translation frame shift resulting in a different termination of amino acid translation and synthesis of a shorter form of AQP10. Thus an AQP10 molecule deduced from the transcript with an insertion has a distinct C‐terminus, different from that translated from the transcript without the insertion. In the present study, we investigated the expression and localization of these AQP10 isoforms. Results. Two transcripts were expressed in human duodenum and jejunum. Western‐blot analysis using antibodies for these AQP10 isoforms immunoblotted two bands of approx. 35 and 30 kDa respectively. Immunohistochemistry and immunoelectron microscopy demonstrated localization of the AQP10 with an insertion in the capillary endothelium in villi of the small intestine and the isoform without the insertion in the gastro‐entero‐pancrestic endocrine cells. Conclusion. The different forms of localization of the AQP10 isoforms indicate that they may play different roles in the proximal portion of human small intestine.