Cuthbert A W, Hickman M E, Thorn P, MacVinish L J
Department of Pharmacology, University of Cambridge, Cambridge CB2 1QJ, United Kingdom.
Am J Physiol. 1999 Jul;277(1):C111-20. doi: 10.1152/ajpcell.1999.277.1.C111.
1-Ethyl-2-benzimidazolone (EBIO) caused a sustained increase in electrogenic Cl(-) secretion in isolated mouse colon mucosae, an effect reduced by blocking basolateral K(+) channels. The Ca(2+)-sensitive K(+) channel blocker charybdotoxin (ChTX) and the cAMP-sensitive K(+) channel blocker 293B were more effective when the other had been added first, suggesting that both types of K(+) channel were activated. EBIO did not cause Cl(-) secretion in cystic fibrosis (CF) colonic epithelia. In apically permeabilized colonic mucosae, EBIO increased the K(+) current when a concentration gradient was imposed, an effect that was completely sensitive to ChTX. No current sensitive to trans-6-cyano-4-(N-ethylsulfonyl-N-methylamino)-3-hydroxy-2, 2-dimethylchromane (293B) was found in this condition. However, the presence of basolateral cAMP-sensitive K(+) channels was demonstrated by the development of a 293B-sensitive K(+) current after cAMP application in permeabilized mucosae. In isolated colonic crypts EBIO increased cAMP content but had no effect on intracellular Ca(2+). It is concluded that EBIO stimulates Cl(-) secretion by activating Ca(2+)-sensitive and cAMP-sensitive K(+) channels, thereby hyperpolarizing the apical membrane, which increases the electrical gradient for Cl(-) efflux through the CF transmembrane conductance regulator (CFTR). CFTR is also activated by the accumulation of cAMP as well as by direct activation.
1-乙基-2-苯并咪唑酮（EBIO）可使离体小鼠结肠黏膜的电生性氯离子分泌持续增加，而阻断基底外侧钾通道可减弱此效应。钙敏感性钾通道阻滞剂蝎毒素（ChTX）和环磷酸腺苷（cAMP）敏感性钾通道阻滞剂293B在预先加入另一种阻滞剂时作用更明显，提示两种类型的钾通道均被激活。EBIO对囊性纤维化（CF）结肠上皮细胞无氯离子分泌作用。在顶端通透的结肠黏膜中，施加浓度梯度时EBIO可增加钾电流，此效应完全对ChTX敏感。在此条件下未发现对反式-6-氰基-4-（N-乙基磺酰基-N-甲氨基）-3-羟基-2,2-二甲基苯并二氢吡喃（293B）敏感的电流。然而，在通透黏膜中应用cAMP后出现293B敏感的钾电流，证明存在基底外侧cAMP敏感性钾通道。在离体结肠隐窝中，EBIO可增加cAMP含量，但对细胞内钙无影响。结论是，EBIO通过激活钙敏感性和cAMP敏感性钾通道刺激氯离子分泌，从而使顶端膜超极化，增加氯离子通过CF跨膜传导调节因子（CFTR）外流的电梯度。CFTR也可被cAMP积累以及直接激活所激活。
