CCK-58 and the Two Component Paradigm for Exocrine Pancreatic Secretion

描述(申请人提供)：胰腺外分泌大量(每天1-2个L)含酶和电解质的水样分泌物。一个由来已久的范例指出，水部分与含有酶的部分是分开调节的，并且两种分泌物来自不同的细胞类型。这就是所谓的双成分假说。其中一个成分，腺泡细胞，将酶合成并包装成酶原颗粒，通过胞吐作用(称为调节分泌)排入导管系统；第二个成分，由导管细胞分泌的水成分，用碱性溶液稀释酶，混合物进入十二指肠。第一种成分是酶，主要由腺泡细胞上的缩胆囊素和乙酰胆碱调节。第二种成分是水，通过分泌素刺激导管细胞(与其他促分泌剂结合)。我们建议对这一范式进行修改。在我们的假设中，腺泡细胞为房水分泌物贡献了相当大的体积(相当于导管细胞)，水/电解质和酶的量之间的关系受到严格的调控。这种调节采取的形式是电解质(K、Cl-、HCO3-)进入酵素颗粒，并在水中渗透吸水，导致颗粒膨胀，通常是其体积的两倍以上。我们认为这种酶原颗粒水是腺泡细胞在调节分泌过程中的主要分泌。此时，用水稀释的颗粒基质被排入导管系统，在那里导管分泌物发生进一步稀释。通过胞吐作用排入导管树的颗粒水的体积可以解释最初在强烈刺激(神经或激素)下分泌的所有液体。这些步骤在许多细胞类型中都得到了很好的证实，包括外分泌胰腺。然而，它们与胰腺功能和疾病的相关性几乎没有受到关注，我们认为，部分原因是它代表了广泛接受的双组分范例的重大背离，因为它意味着水成分(腺泡液)和酶成分的大部分没有单独调节，也不是来自不同的细胞类型。这一假说尚未得到验证，因为腺泡细胞分泌的液体从未被量化过，这与导管液体不同，后者已在体外对分离的胰腺导管进行研究，并在体内使用大鼠模型进行研究，在该模型中，腺泡细胞完全消除，但导管细胞保持完整和功能。我们将使用这个模型，即铜缺乏的大鼠，来检验这样的假设，即荷尔蒙CCK-58从腺泡细胞刺激大量的水和蛋白质，而不是从导管细胞刺激，并且这种CCK-58刺激的液体分泌(但不是分泌素刺激的液体)将在铜缺乏的大鼠中被取消。CCK-58是独一无二的，因为它是老鼠血液中唯一的形式，也是唯一强烈刺激胰腺水和氯化物的形式。该结果可能与胰腺疾病、胰腺炎和囊性纤维化高度相关。 项目简介：外分泌胰腺是分泌消化酶的最重要的器官，它的紊乱会导致几种紊乱，如囊性纤维化和胰腺炎。我们的研究将测试一种关于分泌物如何调节的新假说，这可能会为这些疾病提供新的治疗方法。

DESCRIPTION (provided by applicant): The exocrine pancreas produces a large amount (1-2 L/day) of an aqueous secretion containing enzymes and electrolytes. A long-standing paradigm states that the aqueous portion is regulated separately from the enzyme-containing portion, and that the two secretions originate from separate cell types. This is called the two-component hypothesis. One component, the acinar cell, synthesizes and packages the enzymes in zymogen granules, which are discharged into the duct system via exocytosis (called regulated secretion), and the second component, the aqueous component, secreted by the duct cells, dilutes the enzymes with an alkaline solution and the mixture enters the duodenum. The first component, enzymes, is regulated predominately by cholecystokinin and acetylcholine at the acinar cell. The second component, the aqueous, by secretin stimulation of duct cells (in combination with other secretagogues). We propose a modification of this paradigm. In our hypothesis, the acinar cell contributes a substantial volume (equal to duct cells) to the aqueous secretion, and the relationship of the amount of water/electrolyte to the amount of enzyme is tightly regulated. This regulation takes the form of electrolytes (K+, Cl-, HCO3-) entering the zymogen granule and osmotically drawing in water, and causing the granules to swell, often more than doubling their volume. We suggest that this zymogen granule water is the primary secretion of the acinar cell during regulated secretion. At this point, the granule matrix, diluted with water, is discharged into the ductal system where further dilution with ductal secretions occurs. The volume of granule water discharged into the ductal tree by exocytosis can account for all the fluid initially secreted in response to a strong stimulus (neural or hormonal). These steps are well established in many cell types, including the exocrine pancreas. However, their relevance to pancreatic function and disorders have received little attention, in part, we believe, because it represents a major departure from the widely-accepted two-component paradigm, in that it implies that a major fraction of the aqueous component (acinar fluid) and enzyme component are NOT separately regulated, and do NOT originate from separate cell types. This hypothesis has not been tested, because fluid secretion from acinar cells has never been quantified, in contrast to duct fluid, which has been studied in vitro in isolated pancreatic ducts, and in vivo using a rat model in which the acinar cells are completely eliminated but duct cells remain intact and functional. We will use this model, the copper-deficient rat, to test the hypothesis that the hormone, cholecystokinin-58, stimulates a large amount water and protein from the acinar cell, but not from the duct cells, and that this CCK-58 stimulated fluid secretion (but not secretin-stimulated fluid) will be abolished in copper-deficient rats. CCK-58 is unique, because it is the only form in rat blood and the only form that strongly stimulates water and chloride from the pancreas. The results may be highly relevant to the pancreatic disorders pancreatitis and cystic fibrosis. Project narrative: The disorders of the exocrine pancreas, the most important organ for secreting the digestive enzymes, is subject to several disorders, such as cystic fibrosis and pancreatitis. Our study will test a new hypothesis on how the secretions are regulated that may suggest new treatments for these diseases