Freeman S L, MacNaughton W K
Mucosal Inflammation Research Group and Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1.
Gut. 2004 Feb;53(2):214-21. doi: 10.1136/gut.2003.023895.
Hyporesponsiveness of the intestinal epithelium to secretagogues occurs in different models of intestinal injury, including radiation enteropathy, and in human disease. While this impairment of barrier function has been linked to increased inducible nitric oxide synthase (iNOS) activity, the cellular target of NO in this phenomenon is not known, although recent studies suggest that some isoforms of adenylate cyclase are inhibited by NO.
To determine adenylate cyclase isoform distribution in colonic epithelial cells and, in particular, the physiological significance of NO inhibitable adenylate cyclase isoforms 5 and 6 in radiation induced epithelial secretory dysfunction.
Reverse transcription-polymerase chain reaction (RT-PCR), immunocytochemistry, and immunohistochemistry were used to examine adenylate cyclase expression. The responsiveness of mouse colon to secretagogues 72 hours post-15 Gy gamma radiation or following in vitro exposure to NO donors was measured in Ussing chambers. Also, cAMP, cGMP, and ATP levels were measured.
RT-PCR, immunocytochemistry, and immunohistochemistry showed that adenylate cyclase 5 was expressed in mouse colon, and isoforms 5 and 6 were expressed in human biopsies and intestinal epithelium. Pharmacological studies showed that these isoforms are functionally important in chloride secretion. NO mediated hyporesponsiveness to secretagogues is primarily a result of decreased adenylate cyclase activity, and not G(i) activation or decreased cellular ATP levels.
NO inhibitable isoforms of adenylate cyclase are expressed in mouse and human secretory colonic epithelia, and appear to be the target of radiation induced NO to reduce the responsiveness to cAMP dependent secretagogues.
肠上皮对促分泌剂反应性降低发生在不同的肠损伤模型中，包括放射性肠炎以及人类疾病。虽然这种屏障功能的损害与诱导型一氧化氮合酶（iNOS）活性增加有关，但在这一现象中一氧化氮的细胞靶点尚不清楚，不过最近的研究表明，一些腺苷酸环化酶同工型受到一氧化氮的抑制。
确定腺苷酸环化酶同工型在结肠上皮细胞中的分布，特别是一氧化氮可抑制的腺苷酸环化酶同工型5和6在辐射诱导的上皮分泌功能障碍中的生理意义。
采用逆转录-聚合酶链反应（RT-PCR）、免疫细胞化学和免疫组织化学检测腺苷酸环化酶的表达。在尤斯灌流小室中测量15 Gyγ射线照射后72小时或体外暴露于一氧化氮供体后小鼠结肠对促分泌剂的反应性。同时，测量环磷酸腺苷（cAMP）、环磷酸鸟苷（cGMP）和三磷酸腺苷（ATP）水平。
RT-PCR、免疫细胞化学和免疫组织化学显示，腺苷酸环化酶5在小鼠结肠中表达，同工型5和6在人类活检组织和肠上皮中表达。药理学研究表明，这些同工型在氯化物分泌中具有重要功能。一氧化氮介导的对促分泌剂反应性降低主要是腺苷酸环化酶活性降低的结果，而非G(i)激活或细胞ATP水平降低。
一氧化氮可抑制的腺苷酸环化酶同工型在小鼠和人类分泌性结肠上皮中表达，并且似乎是辐射诱导的一氧化氮降低对cAMP依赖性促分泌剂反应性的靶点。
