Regulation of secretion by bile duct epithelial cells

描述（由申请人提供）：本提案中描述的研究涉及负责胆管细胞分泌的细胞机制，胆管细胞是排列在肝内胆管管腔内的上皮细胞，约占人类胆汁容量的40%。以往的研究表明，胆管细胞的分泌能力会随着生理需求的变化而发生动态变化；并且依赖于选择性地打开单独的Cl-通道，以响应cAMP，胞质Ca2+和细胞体积。值得注意的是，这些通道存在于高度调控的细胞内囊泡中，并且具有足够的容量在几分钟内替换整个胆管细胞质膜的40%。因此，特异目的旨在解决含有离子通道的膜囊泡的运输（内吞作用和胞吐作用）为改变胆管细胞质膜的组成和传导提供了早期和必要的机制，并且对cAMP， Ca2+和细胞体积的分泌反应至关重要。具体目标发生在1)表征负责调节内吞作用和胞吐作用的细胞信号，2)评估囊泡运输和PKCa对调节胆管细胞体积和淋巴管分泌所必需的SKCa通道的直接调节磷酸化的相对作用；3)细胞策略的定义，以维持多蛋白信号复合物负责顶端ATP释放，P2受体分布和K+和Cl-分泌。长期目标是确定参与胆管分泌的细胞机制，并确定通过对胆管细胞的影响而促成胆汁形成的生理因素。因此，这些发现与以胆管细胞功能受损为特征的广泛的胆汁淤积性疾病的诊断和治疗直接相关；以及通过对胆管细胞的作用来改变胆汁体积和成分的药理学方法的发展。

DESCRIPTION (provided by applicant): The studies described in this proposal address the cellular mechanisms responsible for secretion by cholangiocytes, the epithelial cells that line the lumen of intrahepatic bile ducts and account for approximately 40 percent) of bile volume in man. Previous studies indicate that the secretory capacity of cholangiocytes undergoes dynamic changes in response to varying physiologic demands; and depends on selective) penning of separate Cl- channels in response to cAMP, cytosolic Ca2+, and cell volume. Notably, these channels are present in intracellular vesicles that are highly regulated and are of sufficient capacity to replace 40 percent of the entire cholangiocyte plasma membrane within minutes. Accordingly, the Specific Aims are designed to address the working hypothesis that trafficking (endocytosis and exocytosis) of membrane vesicles containing ion channels provides an early and essential mechanism for modifying the composition and conductance of the cholangiocyte plasma membrane and is essential for the secretory responses to cAMP, Ca2+, and cell volume. The Specific Aims occurs on 1) characterization of the cellular signals responsible for regulation of endocytosis and exocytosis, 2) evaluation, of the relative roles of vesicular trafficking and direct regulatory phosphorylation by PKCa of SKCa channels essential for modulation of cholangiocyte volume and Juctular secretion; and 3) definition of the cellular strategies for maintaining the multiprotein signaling complex responsible for apical ATP release, P2 receptor distribution and K+ and Cl- secretion. The long-term goal is to define the cellular mechanisms involved in ductular secretion, and to identify the) physiologic factors which contribute to bile formation through effects on duct cells. Thus, the findings ire directly relevant to diagnosis and management of a broad range of cholestatic disorders characterized by impaired cholangiocyte function; and to development of pharmacologic approaches o modify the volume and composition of bile through effects on duct cells.