A study on the mechanism and reconstruction of secretory process in salivary glands.

我们认为，除了肾上腺素能系统外，M胆碱能系统还参与了狗下颌下腺粘蛋白释放的调节。然而，胞吐粘蛋白释放的确切机制及其调控机制尚不完全清楚。我们先前已经证明，血小板激活因子(PAF)，一种有效的磷脂介质，是通过刺激狗唾液腺中的M胆碱能受体来合成的。本研究探讨了颌下腺PAF生物合成的调节及其在粘蛋白释放中的作用。去甲肾上腺素(NE)和去甲肾上腺素(NE)刺激颌下腺细胞产生PAF，而异丙肾上腺素则无此作用。在ACh、NE、异丙肾上腺素和8BrcAMP处理的细胞中，Lyso-PAF：乙酰-CoA乙酰转移酶被激活。细胞内钙离子浓度的降低可显著降低ACh诱导的激活，但对NE、异丙肾上腺素和8BrcAMP诱导的激活影响不大。二硫苏糖醇…这些药剂还能提高更多的胞内钙磷转移酶的活性，而在培养液中不加钙则进一步提高了酶的活性。部分在豚鼠颌下腺细胞中形成的PAF被释放到孵育液中，而不是狗颌下腺细胞中。PAF刺激豚鼠颌下腺切片释放粘蛋白。PAF的作用呈钙依赖性，并可被PAF受体拮抗剂BN50739拮抗。用RT-PCR方法检测到PAF受体在豚鼠腮腺和颌下腺中有表达，而在狗腮腺和颌下腺中没有表达。豚鼠颌下腺切片中1，4，5-三磷酸肌醇的含量在前5-10s被PAF一过性增加。将颌下腺总mRNA注入非洲爪蛙卵母细胞，表达ACh受体，ACh可产生氯电流，但PAF受体的表达尚未成功(在目前的研究中)。这些结果表明，PAF联结唾液腺是通过依赖于钙的胆碱能系统和α-肾上腺素能系统的重塑途径控制的，豚鼠下颌下腺存在PAF受体，ACh刺激细胞形成的PAF部分释放到细胞外，并通过PAF受体-PI翻转途径刺激粘蛋白的分泌。较少

We have suggested that the muscarinic cholinergic system in addition to the adrenergic system participate in the regulation of mucin release in dog asubmandibular gland. However the precise mechanism of exocytotic mucin release and its regulation mechanisms are not fully understood. We have previously shown that platelet-activating factor (PAF), a potent phospholipid mediator, is synthesized by muscarinic cholinergic receptor stimulation in dog salivary glands. The present study examined the regulation of PAF biosynthesis and its role in mucin release in submandibular glands.Norepinephrine (NE) and phenyrephrine, but not isoproterenol stimulated PAF production in submandibular gland cells. Lyso-PAF : acetyl-CoA acetyltransferase was activated in the cells treated with ACh, NE,isoproterenol and 8Br-cyclic AMP.Deprivation of Ca^<2+> in the medium markedly reduced ACh-induced activation, but little affected NE-, isoproterenol- and 8Br-cyclic AMP-induced activation. Dithiothreitol-insensit … More ive chlinephosphotranseferase activity was also increased by these agents, and the deprivation of Ca^<2+> in the medium further increased the activation. A part of PAF formed in the guinea pig but not dog submandibular gland cells was released into the incubation medium. PAF stimulated the release of mucin from guinea pig submandibular gland slices. The effect of PAF was Ca^<2+>-dependent and antagonized by PAF receptor antagonist BN50739. By the RT-PCR method, the expression of PAF receptor mRNA was found in the guinea pig parotid gland and submandibular gland, but not in the dog parotid gland and submandibular galnd. The amount of inositol 1,4,5-trisphosphate in guinea pig subbmandibular gland slices transiently increased by PAF over the first 5-10s. Injection of total mRNA from submandibular gland in to Xenopus oocytes expressed ACh receptors which produced Cl-current by ACh but the expression of PAF receptor has not been succeded yet (under current investigation).These results suggest that PAF syntesis salivary glands is under the control of muscarinic cholinergic and alpha-adrenergic systems via Ca^<2+>-dependent remodelling pathways and that PAF receptors are existent in guinea pig submandibular galnds, and PAF,formed by the stimulation of cells with ACh, is partially released to the extracellular space and stimulates secretion of mucin via PAF receptor-PI turn over pathway. Less