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Bacgrouns/Aims: Several insulinotropic agents were recently reported to cause β-cell swelling. The possible participation of AQP7 to water transport was investigated in AQP7^{+/ +} or AQP7^-/- mice. Methods: Aquaporin expression, insulin secretion, cell swelling and electrical activity were investigated in pancreatic islets. Results: RT-PCR revealed the expression of AQP5 and AQP8 mRNA. Double immunofluorescent labeling indicated their presence in β-cells. Whilst basal insulin release from isolated pancreatic islets incubated at 2.8 mM D-glucose did not differ between AQP7^{+/ +} or AQP7^-/- mice, the secretion of insulin evoked by the omission of 50 mM NaCl, the substitution of 50 mM NaCl by 100 mM glycerol or a rise in D-glucose concentration to 8.3 mM and 16.7 mM was severely impaired in the islets from AQP7^-/- mice. Yet, exposure of β-cells to either the hypotonic medium or a rise in D-glucose …