Immunolocalization and translocation of aquaporin-5 water channel in sweat glands

BackgroundAquaporin-5 (AQP5) is a member of the water channel protein family. Although AQP5 was shown to be present in sweat glands, the presence or absence of regulated intracellular translocation of AQP5 in sweat glands remained to be determined.ObjectiveWe investigated whether AQP5 in sweat glands translocated during sweating, and also sought to determine the intracellular signal that triggers this translocation.MethodsImmunofluorescent analyses of AQP5 in mouse and human sweat glands were performed. Madin-Darby Canine kidney (MDCK) cell lines stably expressing human AQP5 were generated, and the regulated translocation of AQP5 in the polarized cells was assessed by immunofluorescent analysis and biotinylation assays.ResultsAQP5 showed rapid translocation to the apical membranes during sweating. In human eccrine sweat glands, immunoreactive AQP5 was detected in the apical membranes and the intercellular canaliculi of secretory coils, and in the basolateral membranes of the clear cells. Treatment of human AQP5-expressing MDCK cells with calcium ionophore A23187 resulted in a twofold increase of AQP5 in the apical membranes within 5 min.ConclusionThe regulated AQP5 translocation may contribute to sweat secretion by increasing the water permeability of apical plasma membranes of sweat glands.