Smith S N, Delaney S J, Dorin J R, Farley R, Geddes D M, Porteous D J, Wainwright B J, Alton E W
Ion Transport Unit, National Heart and Lung Institute, London, United Kingdom.
Am J Physiol. 1998 Feb;274(2):C492-9. doi: 10.1152/ajpcell.1998.274.2.C492.
Some cystic fibrosis transmembrane conductance regulator (CFTR) mutations, such as G551D, result in a correctly localized Cl- channel at the cell apical membrane, albeit with markedly reduced function. Patch-clamp studies have indicated that both phosphatase inhibitors and 3-isobutyl-1-methylxanthine (IBMX) can induce Cl- secretion through the G551D mutant protein. We have now assessed whether these agents can induce Cl- secretion in cftrG551D mutant mice. No induction of Cl- secretion was seen with the alkaline phosphatase inhibitors bromotetramisole or levamisole in either the respiratory or intestinal tracts of wild-type or cftrG551D mice. In contrast, in G551D intestinal tissues, IBMX was able to produce a small CFTR-related secretory response [means +/- SE: jejunum, 1.8 +/- 0.9 microA/cm2, n = 7; cecum, 3.7 +/- 0.8 microA/cm2, n = 7; rectum (in vivo), 1.9 +/- 0.9 mV, n = 5]. This was approximately one order of magnitude less than the wild-type response to this agent and, in the cecum, was significantly greater than that seen in null mice (cftrUNC). In the trachea, IBMX produced a transient Cl- secretory response (37.3 +/- 14.7 microA/cm2, n = 6) of a magnitude similar to that seen in wild-type mice (33.7 +/- 4.7 microA/cm2, n = 9). This response was also present in null mice and therefore is likely to be independent of CFTR. No effect of IBMX on Cl- secretion was seen in the nasal epithelium of cftrG551D mice. We conclude that IBMX is able to induce detectable levels of CFTR-related Cl- secretion in the intestinal tract but not the respiratory tract through the G551D mutant protein.
一些囊性纤维化跨膜传导调节因子（CFTR）突变，如G551D，尽管功能明显降低，但仍能在细胞顶端膜上正确定位氯离子通道。膜片钳研究表明，磷酸酶抑制剂和3-异丁基-1-甲基黄嘌呤（IBMX）均可通过G551D突变蛋白诱导氯离子分泌。我们现在评估了这些药物是否能在cftrG551D突变小鼠中诱导氯离子分泌。在野生型或cftrG551D小鼠的呼吸道或肠道中，碱性磷酸酶抑制剂溴四咪唑或左旋咪唑均未诱导出氯离子分泌。相比之下，在G551D肠道组织中，IBMX能够产生与CFTR相关的小分泌反应[平均值±标准误：空肠，1.8±0.9微安/平方厘米，n = 7；盲肠，3.7±0.8微安/平方厘米，n = 7；直肠（体内），1.9±0.9毫伏，n = 5]。这比野生型对该药物的反应小约一个数量级，且在盲肠中，明显大于在基因敲除小鼠（cftrUNC）中观察到的反应。在气管中，IBMX产生了短暂的氯离子分泌反应（37.3±14.7微安/平方厘米，n = 6），其幅度与野生型小鼠中观察到的相似（33.7±4.7微安/平方厘米，n = 9）。这种反应在基因敲除小鼠中也存在，因此可能与CFTR无关。在cftrG551D小鼠的鼻上皮中未观察到IBMX对氯离子分泌的影响。我们得出结论，IBMX能够通过G551D突变蛋白在肠道而非呼吸道中诱导出可检测水平的与CFTR相关的氯离子分泌。
