Cova E, Gong A, Marinelli R A, LaRusso N F
Center for Basic Research in Digestive Diseases, Division of Gastroenterology and Hepatology, Mayo Medical School, Clinic and Foundation, Rochester, MN 55905, USA.
Hepatology. 2001 Sep;34(3):456-63. doi: 10.1053/jhep.2001.27092.
In recent studies using freshly isolated rat cholangiocytes, we established that water crosses the cholangiocyte membrane by a channel-mediated mechanism involving aquaporins, a family of water-channel proteins. Our goal was to address the importance of channel-mediated water transport in ductal bile formation by employing a physiologic experimental model, the enclosed, polarized rat intrahepatic bile duct unit (IBDU). Expansion and reduction of luminal areas as a reflection of water movement into and out of IBDUs prepared from livers of normal rats were measured by quantitative computer-assisted image analysis. When enclosed IBDUs were exposed to inward or outward osmotic gradients, their luminal area rapidly increased (approximately 25%) or decreased (approximately 20%) reflecting net water secretion or absorption, respectively. These effects were specifically inhibited by 2 water channel blockers, DMSO and HgCl2. In both instances, beta-mercaptoethanol reversed the inhibitory effects. In the absence of an osmotic gradient, choleretic agents (secretin and forskolin) and a cholestatic hormone (somatostatin) induced a significant increase or decrease of IBDU luminal area by 21% and 22%, respectively. These effects were also inhibited by DMSO and reversed by beta-mercaptoethanol. Under our experimental conditions, DMSO did not interfere with either forskolin-induced cAMP synthesis or the generation of osmotic driving forces via the apical chloride-bicarbonate exchanger. Protamine, an inhibitor of the paracellular pathway, had no effect on hypotonic or forskolin-induced water secretion in IBDUs. These results in a physiologically relevant model of ductal bile formation provide additional support for the concept that osmotically driven and agonist-stimulated water movement into (secretion) and out of (absorption) the biliary ductal lumen is transcellular and water channel-mediated.
在最近使用新鲜分离的大鼠胆管细胞进行的研究中，我们证实水通过涉及水通道蛋白（一类水通道蛋白家族）的通道介导机制穿过胆管细胞膜。我们的目标是通过采用一种生理学实验模型，即封闭的、极化的大鼠肝内胆管单位（IBDU），来探讨通道介导的水转运在胆管胆汁形成中的重要性。通过定量计算机辅助图像分析测量正常大鼠肝脏制备的IBDU中管腔面积的扩大和缩小，以反映水进出IBDU的情况。当封闭的IBDU暴露于内向或外向渗透梯度时，它们的管腔面积迅速增加（约25%）或减少（约20%），分别反映净水分泌或吸收。这些效应被两种水通道阻滞剂二甲基亚砜（DMSO）和氯化汞（HgCl2）特异性抑制。在这两种情况下，β-巯基乙醇都能逆转抑制作用。在没有渗透梯度的情况下，促胆汁分泌剂（促胰液素和福斯可林）和一种胆汁淤积激素（生长抑素）分别使IBDU管腔面积显著增加或减少21%和22%。这些效应也被DMSO抑制，并被β-巯基乙醇逆转。在我们的实验条件下，DMSO既不干扰福斯可林诱导的环磷酸腺苷（cAMP）合成，也不干扰通过顶端氯-碳酸氢根交换体产生的渗透驱动力。鱼精蛋白是细胞旁途径的抑制剂，对IBDU中的低渗或福斯可林诱导的水分泌没有影响。这些在胆管胆汁形成的生理相关模型中的结果为以下概念提供了额外支持：渗透驱动和激动剂刺激的水进入（分泌）和流出（吸收）胆管管腔是跨细胞的且由水通道介导。
