Different expression and subcellular localization of vesicular inhibitory amino acid transporter in ducts of major salivary glands: An in situ study in mice

Objective: The aim of this study was to clarify the mechanism of GABA (rectangle-amino butyric acid)-signaling in the salivary glands by localization of vesicular inhibitory amino acid transporter, a key molecule in GABA-synthesis. Design: Parotid, sublingual and submandibular glands of mice at various postnatal stages were examined in immuno-light and electron microscopy as well as immuno-blotting. Results: Expression for vesicular inhibitory amino acid transporter was detected in parotid and sublingual glands of both sexes and female submandibular gland throughout postnatal development, while it was negligible in male submandibular glands at and after puberty. The expression in female submandibular glands attenuated after testosterone injection. The immunoreactivity was localized in striated ductal cells, but not acinar cells, in the salivary glands, and it occurred in association with intracellular and plasma membranes of the cells. It also occurred in myoepithelial and vascular smooth muscle cells. Conclusions: GABA-signaling was suggested to be a significant signaling pathway in salivary ductal cells, which was suppressed in male submandibular glands at and after puberty. The suppression in the submandibular duct was by testosterone. In addition, the participation of vesicular inhibitory amino acid transporter in GABA signaling through plasma membranes of the ductal cells was suggested. The significance of occurrence of the immunoreactivity in myoepithelial and smooth muscle cells remains to be further elucidated in terms of implication in GABA signaling.