Narins S C, Ramakrishnan R, Park E H, Smith P R, Meyers W C, Abedin M Z
Drexel University College of Medicine, Philadelphia, PA 19102-1192, USA.
Eur J Clin Invest. 2005 Aug;35(8):514-22. doi: 10.1111/j.1365-2362.2005.01520.x.
Gallbladder Na+ and H2O absorption are increased prior to gallstone formation and may promote cholesterol nucleation. Na+/H+ exchange (NHE) isoforms NHE2 and NHE3 are involved in gallbladder Na+ transport in prairie dogs. We examined whether increased gallbladder Na+ absorption observed during early gallstone formation is the result of NHE up-regulation.
Native gallbladder and primary cultures of gallbladder epithelial cells (GBECs) harvested from prairie dogs fed nonlithogenic (CON) or 1.2% cholesterol diet for varying lengths of time to induce cholesterol-saturated bile (PreCRYS), cholesterol crystals (CRYS), or gallstones (GS) were used. NHE activity was assessed by measuring dimethylamiloride-inhibitable 22Na+ uptake under H+ gradient in primary GBECs. HOE-694 was used to determine NHE2 and NHE3 contributions. NHE protein and mRNA expression were examined by Western and Northern blots, respectively.
Gallbladder total NHE activity was 25.1 +/- 1.3 nmol mg protein(-1) min(-1) in the control and increased during gallstone formation peaking at the PreCRYS stage (98.4 +/- 3.9 nmol mg protein(-1) min(-1)). There was a shift in NHE activity from NHE2 to NHE3 as the animals progressed from no stones through the PreCRYS and CRYS stages to gallstones. The increase in NHE activity was partly caused by an increased Vmax without any change in K(Na)m. Both NHE2 and NHE3 protein increased moderately during the PreCRYS stage without increases in mRNA expression.
Increased gallbladder Na+ absorption observed prior to crystal formation is in part caused by an increase NHE activity which is not fully accounted for by an increase in NHE proteins and mRNA levels but may be explained by enhanced localization in the membranes and/or altered regulation of NHE.
在胆结石形成之前，胆囊对钠离子和水的吸收增加，这可能会促进胆固醇成核。钠离子/氢离子交换（NHE）亚型NHE2和NHE3参与草原犬鼠胆囊的钠离子转运。我们研究了在胆结石形成早期观察到的胆囊钠离子吸收增加是否是NHE上调的结果。
使用从喂食非致石性（对照）或1.2%胆固醇饮食不同时间以诱导胆固醇饱和胆汁（PreCRYS）、胆固醇晶体（CRYS）或胆结石（GS）的草原犬鼠收获的天然胆囊和胆囊上皮细胞（GBECs）原代培养物。通过在原代GBECs中在氢离子梯度下测量二甲氨氯吡脒抑制的22Na+摄取来评估NHE活性。使用HOE-694来确定NHE2和NHE3的贡献。分别通过蛋白质印迹和Northern印迹检查NHE蛋白和mRNA表达。
对照组胆囊总NHE活性为25.1±1.3 nmol mg蛋白-1 min-1，在胆结石形成过程中增加，在PreCRYS阶段达到峰值（98.4±3.9 nmol mg蛋白-1 min-1）。随着动物从无结石状态经历PreCRYS和CRYS阶段到胆结石阶段，NHE活性从NHE2向NHE3发生转变。NHE活性的增加部分是由Vmax增加引起的，而Km(Na)没有变化。在PreCRYS阶段，NHE2和NHE3蛋白均适度增加，而mRNA表达没有增加。
在晶体形成之前观察到的胆囊钠离子吸收增加部分是由NHE活性增加引起的，NHE蛋白和mRNA水平的增加并不能完全解释这种增加，但可能是由于膜定位增强和/或NHE调节改变所致。
