Relationship between proteins related to exocytosis regulation in salivary glands

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In salivary glands, stimulation of β-adrenergic and muscarinic cholinergic receptors provokes exocytotic secretion of proteins. Cellular cAMP level and intracellular Ca2+ concentration are increased by activation of β-adrenergic and muscarinic cholinergic receptors, respectively, and they play as cellular signals. We investigated relationship between proteins related to exocytosis regulation and its cell signaling in salivary glands, and demonstrated several results. 1 We established a primary culture system of rat parotid acinar cells, which kept regulatory exocytotic functions provoked by β-adrenergic and muscarinic cholinergic receptor activation. 2)We confirmed the presence of aquaporirn-5 water channels in secretory granules of the rat parotid gland, and suggested that the water channels are involved in granule osmoregulation related to Cl- transport. 3)We demonstrated that the activity of nitric oxide synthase, which is activated by muscarinic receptor activation via increase in intracellular Ca2+, was regulated by phospholipids such as phosphatidyl inositol 4,5-bisphosphate and phosphachidic acid in the rabbit submandibular gland. 4)We demonstrated that cyclic nucleotide phosphodiesterases 1 and 2 were involved in the regulation of cellular cGMP level induced by muscarinic receptor activation in rabbit submandibular gland cells. 5)We found that two kinds of Ca2+/calmodulin-dependent cyclic nucleotide phosphodiesterase, which were activated by Ca2+ levels induced by muscarinic receptor activation, in rabbit parotid acinar cells. 6)We suggested the relationship between changes of membrane domain (detergent-resistant membrane domains) and syntaxin 6, which is considered to be related to maturation of secretory granules. We believe that these results are new information on salivary gland function.