Grubb B R, Lee E, Pace A J, Koller B H, Boucher R C
Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599-7248, USA.
Am J Physiol Gastrointest Liver Physiol. 2000 Oct;279(4):G707-18. doi: 10.1152/ajpgi.2000.279.4.G707.
The Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) located on the basolateral membrane of intestinal epithelia has been postulated to be the major basolateral Cl(-) entry pathway. With targeted mutagenesis, mice deficient in the NKCC1 protein were generated. The basal short-circuit current did not differ between normal and NKCC1 -/- jejuna. In the -/- jejuna, the forskolin response (22 microA/cm(2); bumetanide insensitive) was significantly attenuated compared with the bumetanide-sensitive response (52 microA/cm(2)) in normal tissue. Ion-replacement studies demonstrated that the forskolin response in the NKCC1 -/- jejuna was HCO(3)(-) dependent, whereas in the normal jejuna it was independent of the HCO(3)(-) concentration in the buffer. NKCC1 -/- ceca exhibited a forskolin response that did not differ significantly from that of normal ceca, but unlike that of normal ceca, was bumetanide insensitive. Ion-substitution studies suggested that basolateral HCO(3)(-) as well as Cl(-) entry (via non-NKCC1) paths played a role in the NKCC1 -/- secretory response. In contrast to cystic fibrosis mice, which lack both basal and stimulated Cl(-) secretion and exhibit severe intestinal pathology, the absence of intestinal pathology in NKCC1 -/- mice likely reflects the ability of the intestine to secrete HCO(3)(-) and Cl(-) by basolateral entry mechanisms independent of NKCC1.
位于肠上皮细胞基底外侧膜上的钠-钾-2氯协同转运蛋白（NKCC1）被认为是基底外侧氯离子进入的主要途径。通过靶向诱变，生成了NKCC1蛋白缺陷的小鼠。正常空肠和NKCC1基因敲除空肠的基础短路电流没有差异。在基因敲除空肠中，与正常组织中布美他尼敏感反应（52微安/平方厘米）相比，福斯可林反应（22微安/平方厘米；布美他尼不敏感）明显减弱。离子置换研究表明，NKCC1基因敲除空肠中的福斯可林反应依赖于HCO₃⁻，而在正常空肠中，它与缓冲液中HCO₃⁻的浓度无关。NKCC1基因敲除盲肠表现出的福斯可林反应与正常盲肠没有显著差异，但与正常盲肠不同的是，它对布美他尼不敏感。离子替代研究表明，基底外侧HCO₃⁻以及氯离子进入（通过非NKCC1）途径在NKCC1基因敲除小鼠的分泌反应中起作用。与囊性纤维化小鼠不同，囊性纤维化小鼠既缺乏基础氯离子分泌也缺乏刺激后的氯离子分泌，并表现出严重的肠道病理改变，而NKCC1基因敲除小鼠没有肠道病理改变，这可能反映了肠道通过独立于NKCC1的基底外侧进入机制分泌HCO₃⁻和Cl⁻的能力。
