Physiology and Biochemistry of Saliva Secretion

Vesicles containing proteins destined for intracellular use in lysosomes or outer membranes bud off from the trans face of the Golgi. Depending on their contents, some of the vesicles are diverted to nonsecretory vesicles by the presence of phosphomannose residues on their N-linked glycans or by possessing domains rich in hydrophobic amino acids. At the apical surface of salivary acini, the remaining vesicles accumulate as secretory vesicles. These vesicles become surrounded by myofibrils, which move the secretory vesicles to the cell membrane where they fuse and expel the saliva secretion into a small duct. The odor or taste of food provides a neuronal stimulus to the gland s myofibrils, and this stimulates salivary secretion. 

Water is secreted separately. Neurotransmitters activate a 28-kDa integral membrane protein, aquaporin-5 (AQP5), one of 13 aquaporins in mammals. AQP5 is localized in lipid rafts in the plasma membrane of salivary cells and translocates to the apical plasma 

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