Sellers Zachary M, Childs Debbie, Chow Jimmy Y C, Smith Anders J, Hogan Daniel L, Isenberg Jon I, Dong Hui, Barrett Kim E, Pratha Vijaya S
Div. of Gastroenterology (8414 University of California San Diego Medical Center, 200 West Arbor Dr., San Diego, CA 92103-8414, USA.
Am J Physiol Gastrointest Liver Physiol. 2005 Apr;288(4):G654-63. doi: 10.1152/ajpgi.00386.2004. Epub 2004 Oct 28.
The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) is an important pathway for duodenal mucosal bicarbonate secretion. Duodenal biopsies from CF patients secrete bicarbonate in response to heat-stable enterotoxin from Escherichia coli (STa) but not cAMP. To explore the mechanism of STa-induced bicarbonate secretion in CF more fully, we examined the role of CFTR in STa-stimulated duodenal bicarbonate secretion in mice. In vivo, the duodenum of CFTR (-/-) or control mice was perfused with forskolin (10(-4) M), STa (10(-7) M), uroguanylin (10(-7) M), 8-bromoguanosine 3',5'-cGMP (8-Br-cGMP) (10(-3) M), genistein (10(-6) M) plus STa, or herbimycin A (10(-6) M) plus STa. In vitro, duodenal mucosae were voltage-clamped in Ussing chambers, and bicarbonate secretion was measured by pH-stat. The effect of genistein, DIDS (10(-4) M), and chloride removal was also studied in vitro. Control, but not CF, mice produced a significant increase in duodenal bicarbonate secretion after perfusion with forskolin, uroguanylin, or 8-Br-cGMP. However, both control and CF animals responded to STa with significant increases in bicarbonate output. Genistein and herbimycin A abolished this response in CF mice but not in controls. In vitro, STa-stimulated bicarbonate secretion in CF tissues was inhibited by genistein, DIDS, and chloride-free conditions, whereas bicarbonate secretion persisted in control mice. In the CF duodenum, STa can stimulate bicarbonate secretion via tyrosine kinase activity resulting in apical Cl(-)/HCO(3)(-) exchange. Further studies elucidating the intracellular mechanisms responsible for such non-CFTR mediated bicarbonate secretion may lead to important therapies for CF.
囊性纤维化（CF）跨膜传导调节因子（CFTR）是十二指肠黏膜碳酸氢盐分泌的重要途径。CF患者的十二指肠活检组织在受到大肠杆菌热稳定肠毒素（STa）刺激时会分泌碳酸氢盐，但对环磷酸腺苷（cAMP）无反应。为了更全面地探究STa诱导CF患者碳酸氢盐分泌的机制，我们研究了CFTR在STa刺激的小鼠十二指肠碳酸氢盐分泌中的作用。在体内，向CFTR基因敲除（-/-）小鼠或对照小鼠的十二指肠灌注福斯可林（10^(-4) M）、STa（10^(-7) M）、尿鸟苷素（10^(-7) M）、8-溴鸟苷3',5'-环鸟苷酸（8-Br-cGMP）（10^(-3) M）、染料木黄酮（10^(-6) M）加STa或除莠霉素A（10^(-6) M）加STa。在体外，将十二指肠黏膜置于尤斯灌流小室中进行电压钳制，并用pH计测量碳酸氢盐分泌。还在体外研究了染料木黄酮、二异丁基氨磺酰基苯甲酸盐（DIDS，10^(-4) M）和去除氯离子的影响。对照小鼠而非CF小鼠在灌注福斯可林、尿鸟苷素或8-Br-cGMP后十二指肠碳酸氢盐分泌显著增加。然而，对照动物和CF动物对STa的反应均为碳酸氢盐分泌显著增加。染料木黄酮和除莠霉素A消除了CF小鼠的这种反应，但对照小鼠未受影响。在体外，染料木黄酮、DIDS和无氯条件抑制了CF组织中STa刺激的碳酸氢盐分泌，而对照小鼠的碳酸氢盐分泌持续存在。在CF十二指肠中，STa可通过酪氨酸激酶活性刺激碳酸氢盐分泌，导致顶端氯离子/碳酸氢根离子交换。进一步阐明负责这种非CFTR介导的碳酸氢盐分泌的细胞内机制的研究可能会带来针对CF的重要治疗方法。
