Functional characterization and localization of AQP3 in the human colon

SILBERSTEIN C, KIERBEL A, AMODEO G, ZOTTA E, BIGI F, BERKOWSKI D, IBARRA C

BRAZILIAN JOURNAL OF MEDICAL AND BIOLOGICAL RESEARCH

Associacao Brasileira De Divulgacao Cientifica

Año: 1999 vol. 32 p. 1303 - 1313

0100-879X

Water channels or aquaporins (AQPs) have been identified in a largevariety of tissues. Nevertheless, their role in the human gastrointestinaltract, where their action is essential for the reabsorption andsecretion of water and electrolytes, is still unclear. The purpose of thepresent study was to investigate the structure and function of waterchannels expressed in the human colon. A cDNA fragment of about420 bp with a 98% identity to human AQP3 was amplified fromhuman stomach, small intestine and colon by reverse transcriptionpolymerase chain reaction (RT-PCR) and a transcript of 2.2 kb wasexpressed more abundantly in colon than in jejunum, ileum andstomach as indicated by Northern blots. Expression of mRNA fromthe colon of adults and children but not from other gastrointestinalregions in Xenopus oocytes enhanced the osmotic water permeability,and the urea and glycerol transport in a manner sensitive to anantisense AQP3 oligonucleotide, indicating the presence of functionalAQP3. Immunocytochemistry and immunofluorescence studies inhuman colon revealed that the AQP3 protein is restricted to the villusepithelial cells. The immunostaining within these cells was moreintense in the apical than in the basolateral membranes. The presenceof AQP3 in villus epithelial cells suggests that AQP3 is implicated inwater absorption across human colonic surface cells.