Water Channel Protein AQP3 Is Present in Epithelia Exposed to the Environment of Possible Water Loss

Abstract

SUMMARY Aquaporins (AQPs) are membrane water channel proteins expressed in various tissues in the body. We surveyed the immunolocalization of AQP3, an isoform of the AQP family, in rat epithelial tissues. AQP3 was localized to many epithelial cells in the urinary, digestive, and respiratory tracts and in the skin. In the urinary tract, AQP3 was present at transitional epithelia. In the digestive tract, abundant AQP3 was found in the stratified epithelia in the upper part, from the oral cavity to the forestomach, and in the simple and stratified epithelia in the lower part, from the distal colon to the anal canal. In the respiratory tract, AQP3 was present in the pseudostratified ciliated epithelia from the nasal cavity to the intrapulmonary bronchi. In the skin, AQP3 was present in the epidermis. Interestingly, AQP3 was present at the basal aspects of the epithelia: in the basolateral membranes in the simple epithelia and in the multilayered epithelia at plasma membranes of the basal to intermediate cells. During development of the skin, AQP3 expression commenced late in fetal life. Because these AQP3-positive epithelia have a common feature, i.e., they are exposed to an environment of possible water loss, we propose that AQP3 could serve as a water channel to provide these epithelial cells with water from the subepithelial side to protect them against dehydration. Rapid water movement across the plasma membranes of cells is mediated by the membrane water channel proteins, aquaporins (AQPs). Ten isoforms of the AQP family have been thus far identified in mammals (AQP0-AQP9: for review see Brown et

The laxative effect of bisacodyl is attributable to decreased aquaporin-3 expression in the colon induced by increased PGE2secretion from macrophages

“…It was previously known that AQP3 are expressed in large quantities on the basal side of mucosal epithelial cells in the colon (22); however, the results of this study show that AQP3 is expressed on both the apical and basal sides of mucosal epithelial cells in the colon (Fig. 1B).…”

Aquaporins in sperm osmoadaptation: an emerging role for volume regulation

“…Alternatively, we hypothesize that AQP3 may function as a part of the membrane osmosensing/mechanosensing system for the initial sensing of cell swelling and therefore, may "trigger" subsequent RVD events such as solute transport and cytoskeleton reconstruction. This hypothesis is supported by the fact that AQP3 is strongly expressed in many organs, such as the bladder, trachea and esophagus, and in olfactory cells [18,28,29] , where they seem to have no obvious requirements for rapid water movement but need sensitive perception of tension, shear stress and so on. Moreover, this hypothesis is supported by the recent discovery that AQP5 is actively involved in salivary gland cell RVD by coordinating with TRPV4, a volume sensitive calcium channel, to concertedly regulate cell volume under hypotonic stimulation [23] .…”

Expression and Localization of Aqua-glyceroporins AQP3 and AQP9 in Rat Oral Epithelia

“…These channels have been identified and shown to play an essential role in diverse physiologic processes, including renal water re-absorption, exocrine gland secretion, and lacrimation. Furthermore, other studies have also shown evidence to support their role in cerebrospinal fluid secretion and re-absorption, generation of pulmonary secretion, and aqueous humour secretion 2,10,22,23,26,28,37) . AQP3 has been reported to be expressed in the kidney, urinary tract, digestive tract, and skin 2,10,22,23,26,28,31,37) .…”

“…Furthermore, other studies have also shown evidence to support their role in cerebrospinal fluid secretion and re-absorption, generation of pulmonary secretion, and aqueous humour secretion 2,10,22,23,26,28,37) . AQP3 has been reported to be expressed in the kidney, urinary tract, digestive tract, and skin 2,10,22,23,26,28,31,37) . It has been localized in the basal and intermediate cells of stratified squamous epithelia from the fauces to the forestomach and skin 26) , and has also been detected in the suprabasal layer of the oral epithelium during human and mouse tooth development 11,40) .…”