Physiological characteristics and molecular identity of HCO_3-conductance in pancreatic duct cells.

我们利用从豚鼠和转基因小鼠分离的胰管小叶间段研究了hco_3在胰管细胞顶膜上转运的分子机制。作为一项临床研究，我们检测了日本人囊性纤维化跨膜传导调节因子CFTR的多态性，并建立了一种测量汗液浓度的简单方法。引入人AF508突变的AF小鼠囊性纤维化模型离体胰管，camp刺激的液体分泌能力极差，顶膜Na^+-H^+交换（NHE）活性较强。根尖NHE活性的增强可能与pH的降低和胰液的酸化有关。slc26a6小鼠根尖[CI^-]_i/[HCO_3^-]_o交换的HCO_3-内流模式显著增加，而根尖[C1^-]_i/[HCO_3^-]_o交换的HCO_3-外流模式显著降低，提示slc26a6介导的HCO_3"转运具有单向性。在体内收集纯胰液时，WT小鼠与slc26a6小鼠的胰液体积和pH值均无差异。在光灌注的离体胰管中，在抑制基底侧HCO_3^-运输的情况下，通过调节K^+浓度引起细胞内pH的变化，证明了HCO_3^-的电致传输（HCO_3^-电导）通过根尖膜。心房颤动小鼠离体导管的顶端HCO_3^-电导不依赖于心房颤动，并被消除。这些数据表明CFTR在胰管细胞中作为HCO_3通道起作用。

We have investigated molecular mechanisms for HCO_3-transport across the apical membrane of pancreatic duct cells using interlobular pancreatic duct segments isolated from guinea-pig and transgenic mice. As a clinical research, we examined polymorphisms of CFTR (cystic fibrosis transmembrane conductance regulator) in Japanese and established a simple method to measure concentration in sweat.1. Isolated pancreatic ducts from AF mice, a cystic fibrosis model that human AF508 mutation was introduced, had very poor capacity for cAMP-stimulated fluid secretion and stronger activity of of Na^+-H^+ exchange (NHE) in the apical membrane. The enhanced of apical NHE activity may be involved in decrease of pH and acidification of pancreatic juice.2. The HCO_3--influx mode of apical [CI^-]_i/[HCO_3^-]_o exchange was dramatically increased in slc26a6 null mice, whereas the HCO_3^--efflux mode of apical [C1^-]_i/[HCO_3^-]_o exchange was decreased in slc26a6 null mice, suggesting the uni-directionality of the slc26a6-mediated HCO_3" transport. When pure pancreatic juice was collected in vivo, neither juice volume nor its pH showed differences between WT and slc26a6 null mice.3. The electrogenic HCO_3^-transport (HCO_3^-conductance) across the apical membrane was demonstrated in luminally-perfused isolated pancreatic ducts as changes in intracellular pH induced by manipulation of bath K^+ concentration in the condition that basolateral HCO_3^-transport was inhibited. The apical HCO_3^- conductance was not dependent on and was abolished in isolated ducts from AF mice. The data suggest that CFTR works as a HCO_3" channel in pancreatic duct cells.