Roberts S K, Yano M, Ueno Y, Pham L, Alpini G, Agre P, LaRusso N F
Department of Internal Medicine, Mayo Clinic, Rochester, MN 55905.
Proc Natl Acad Sci U S A. 1994 Dec 20;91(26):13009-13. doi: 10.1073/pnas.91.26.13009.
Cholangiocytes line the intrahepatic bile ducts and regulate salt and water secretion during bile formation, but the mechanism(s) regulating ductal water movement remains obscure. A water-selective channel, the aquaporin CHIP, was recently described in several epithelia, so we tested the hypothesis that osmotic water movement by cholangiocytes is mediated by CHIP. Isolated rodent cholangiocytes showed a rapid increase in volume in the presence of hypotonic extracellular buffers; the ratio of osmotic to diffusional permeability coefficients was > 10. The osmotically induced increase in cholangiocyte volume was inversely proportional to buffer osmolality, independent of temperature, and reversibly blocked by HgCl2. Also, the luminal area of isolated, enclosed bile duct units increased after exposure to hypotonic buffer and was reversibly inhibited by HgCl2. RNase protection assays, anti-CHIP immunoblots, and immunocytochemistry confirmed that CHIP transcript and protein were present in isolated cholangiocytes but not in hepatocytes. These results demonstrate that (i) isolated cholangiocytes and intact, polarized bile duct units manifest rapid, mercury-sensitive increases in cell size and luminal area, respectively, in response to osmotic gradients and (ii) isolated cholangiocytes express aquaporin CHIP at both the mRNA and the protein level. The data implicate aquaporin water channels in the transcellular movement of water across cholangiocytes lining intrahepatic bile ducts and provide a plausible molecular explanation for ductal water secretion.
胆管细胞排列于肝内胆管，在胆汁形成过程中调节盐和水的分泌，但调节胆管水流动的机制仍不清楚。一种水选择性通道——水通道蛋白CHIP，最近在几种上皮细胞中被发现，因此我们验证了这样一个假设：胆管细胞的渗透水流动是由CHIP介导的。分离的啮齿动物胆管细胞在低渗细胞外缓冲液存在时体积迅速增加；渗透渗透系数与扩散渗透系数之比>10。渗透诱导的胆管细胞体积增加与缓冲液渗透压成反比，与温度无关，并被HgCl2可逆性阻断。此外，分离的封闭胆管单位在暴露于低渗缓冲液后管腔面积增加，并被HgCl2可逆性抑制。核糖核酸酶保护分析、抗CHIP免疫印迹和免疫细胞化学证实，CHIP转录本和蛋白存在于分离的胆管细胞中，而不存在于肝细胞中。这些结果表明：（i）分离的胆管细胞和完整的极化胆管单位分别对渗透梯度表现出细胞大小和管腔面积的快速、汞敏感增加；（ii）分离的胆管细胞在mRNA和蛋白水平均表达水通道蛋白CHIP。这些数据表明水通道蛋白水通道参与了跨肝内胆管内衬胆管细胞的水的跨细胞运动，并为胆管水分泌提供了一个合理的分子解释。
