Guanylin and uroguanylin in the parotid and submandibular glands: potential intrinsic regulators of electrolyte secretion in salivary glands

The intestinal peptides guanylin and uroguanylin regulate the electrolyte/w ater transport in the gastrointestinal epithelium via activation of cystic fibrosis transmembrane conductance regulator (CFTR), the cystic fibrosis ge ne product. Because a major but incompletely understood function of the sal ivary glands is the CFTR-mediated secretion of an electrolyte-rich fluid, w e investigated the rat and guinea pig parotid and submandibular glands for expression, cellular distribution, and subcellular localization of guanylin and uroguanylin. RT-PCR analyses with guanylin and uroguanylin-specific pr imers revealed that both peptides are highly expressed in the parotid and s ubmandibular glands. At the translational level, western blotting analyses with peptide-specific guanylin and uroguanylin antibodies identified the ex pected 12.5-kDa immunoreactive peptides in these organs. At the cellular le vel, guanylin and uroguanylin were exclusively confined to epithelial cells of the intralobular and interlobular ducts. At the subcellular level, the immunoreactivities were localized by preembedding immunoelectron microscopy to small vesicles which were concentrated at the apical part of the secret ory epithelial cells. The expression and cell-specific localization of guan ylin and uroguanylin in the salivary glands indicate that these peptides ma y be specifically involved in the regulation of CFTR-mediated electrolyte/w ater secretion in the salivary gland ductal system.