Distribution and roles of aquaporins in salivary glands

Salivary glands are involved in secretion of saliva, which is known to participate in the protection and hydratation of mucosal structures within the oral cavity, oropharynx and oesophagus, the initiation of digestion, some antimicrobial defence, and the protection from chemical and mechanical stress. Saliva secretion is a watery fluid containing electrolytes and a mixture of proteins and can be stimulated by muscarinic and adrenergic agonists. Since water movement is involved in saliva secretion, the expression, localization and function of aquaporins (AQPs) have been studied in salivary glands. This review will focus on the expression, localization and functional roles of the AQPs identified in salivary glands. The presence of AQP1, AQP5 and AQP8 has been generally accepted by many, while the presence of AQP3, AQP4, AQP6 and AQP7 still remains controversial. Functionally, AQP5 seems to be the only AQP thus far to be clearly playing a major role in the salivary secretion process. Modifications in AQPs expression and/or distribution have been reported in xerostomic conditions.