MECHANISM OF EXOCYTOTIC MUCIN RELEASEIN SUBLINGUAL GLAND

在唾液腺腺泡细胞中，分泌功能通过两条主要的信号通路来调节，这两条信号通路分别是毒蕈碱受体和β-肾上腺素能受体，毒蕈碱受体的刺激引起细胞内钙离子（Ca^2+）的增加。然而，Ca^<2+>依赖性分泌途径的作用机制尚未完全阐明。本研究通过Ca^<2+>信号通路研究胞吐作用的机制，首次证实了毒蕈碱受体激活引起的胞内Ca^<2+>升高激活了一氧化氮合酶。随后，一氧化氮产生刺激可溶性鸟苷酸环化酶和诱导唾液腺腺泡细胞环GMP的形成。我们接下来发现，Arfi，一个小的GTP结合蛋白，存在于大鼠腮腺腺泡细胞。此外，我们还证明了在GTP γ S存在下Arf 1转位到分泌颗粒中。大鼠舌下腺腺泡细胞是研究Ca^2+依赖性胞吐的有用模型，因为Ca^2+动员受体激活可诱导粘蛋白胞吐。免疫印迹法检测到syntaxin 1A在大鼠舌下腺腺泡细胞膜上有高浓度的表达，并在大鼠颌下腺和舌下腺中检测到syntaxin 1A mRNA的表达。然而，我们没有检测到syntaxin 1A的结合蛋白，如VAMP-2和SNAP-25。进一步研究syntaxin 1A与Ca^2+-nitric oxide-cyclicGMP信号通路的关系以及syntaxin 1A结合蛋白的鉴定是必要的。

In salivary gland acinar cells, the secretory function is rcgulated by two main signaling pathways via muscarinic and beta-adrenergic receptors.Stimulation of muscarinic receptors causes the increase in intracellular calcium ions (Ca^<2+>). However, the mechanism with Ca^<2+>-dependent secretory pathway has not well elucidated. We here studied with the mechanism of exocytosis via Ca^<2+> signaling pathway.During this study, we first demonstrated that the increase in intracellular Ca^<2+> induced by muscarinic receptor stimulation activated nitric oxide synthase. Subsequently, nitric oxide generated stimulated soluble guanylyl cyclase and induced cyclic GMP formation in salivary gland acinar cells. We next found that Arfi, a small GTP-binding protein, existed in rat parotid acinar cells. Furthermore, we demonstrated that the Arf1 translocated to secretory granules in the presence of GTP gammaS.Rat sublingual gland acinar cells are an useful model for the study with Ca^<2+>-dependent exocytosis, since Ca^<2+>-mobilizing receptor activation induces mucin exocytosis. We found that high concentration of syntaxin1A in the membrane fraction of sublingual acinar cells by immuno blotting.The expression of mRNA of syntaxin1A was detected in rat salivary glands such as sublingual and submandibular glands. However, we failed to detectthe binding proteins to syntaxinlA such as VAMP-2 and SNAP-25.Further studies with the relationship between syntaxin1A and Ca^<2+>-nitric oxide-cyclic GMP signaling and identification of syntaxin 1A binding proteins are necessary.