Schultheiss G, Ribeiro R, Diener M
Institut für Veterinär-Physiologie, Justus-Liebig-Universität Giessen, Germany.
Pflugers Arch. 2001 Jul;442(4):603-13. doi: 10.1007/s004240100574.
Ca2+-dependent secretagogues evoke only a transient Cl- secretion in intestinal epithelia, although they induce a prolonged increase in the intracellular Ca2+ concentration, suggesting that they may exert an additional antisecretory action. In order to study the mechanism of this antisecretory effect, Cl- secretion, measured as the increase in short-circuit current (Isc), was evoked by carbachol in the absence and presence of different inhibitors. Neither a calmodulin antagonist, calmidazolium, nor different inhibitors of the nitric oxide (NO) pathway, i.e. Nomega-nitro-L-arginine (L-NNA) and Nomega-nitro-L-arginine methylester (L-NAME), affected the carbachol-induced Isc. However, inhibition of phospholipases A2 (PLA2) by quinacrine or arachidonyltrifluoromethyl ketone (AACOCF3) enhanced the Isc response evoked by carbachol, suggesting a role of fatty acids in the downregulation of anion secretion. Neither econazole, a cytochrome P450 inhibitor, nor nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenases, mimicked the action of the PLA2 blockers. Conversely, short- or medium-chain fatty acids inhibited the carbachol- and forskolin-induced Isc with caprate (C10:0) being the most efficient water-soluble fatty acid. This fatty acid inhibited a Cl- current, which was driven across the apical membrane by a serosally to mucosally directed Cl- gradient after depolarization of the basolateral membrane. A second action site of fatty acids seems to be the basolateral membrane. After permeabilization of the apical membrane with the ionophore nystatin, a mucosally to serosally directed K+ gradient induced a K+ current, which was also inhibited by caprate. These results indicate that carbachol not only acts as a secretagogue but at the same time initializes downregulation by increasing the intracellular concentration of fatty acids, a mechanism limiting the resulting Cl- secretion.
钙离子依赖型促分泌剂在肠上皮细胞中仅引起短暂的氯离子分泌，尽管它们会诱导细胞内钙离子浓度的持续升高，这表明它们可能发挥额外的抗分泌作用。为了研究这种抗分泌作用的机制，在有无不同抑制剂的情况下，用卡巴胆碱诱发氯离子分泌，并以短路电流（Isc）的增加来衡量。钙调蛋白拮抗剂氯米帕明以及一氧化氮（NO）途径的不同抑制剂，即Nω-硝基-L-精氨酸（L-NNA）和Nω-硝基-L-精氨酸甲酯（L-NAME），均不影响卡巴胆碱诱导的Isc。然而，奎纳克林或花生四烯酰三氟甲基酮（AACOCF3）对磷脂酶A2（PLA2）的抑制作用增强了卡巴胆碱诱发的Isc反应，这表明脂肪酸在阴离子分泌的下调中起作用。细胞色素P450抑制剂酮康唑和脂氧合酶抑制剂去甲二氢愈创木酸（NDGA）均未模拟PLA2阻滞剂的作用。相反，短链或中链脂肪酸抑制了卡巴胆碱和福斯高林诱导的Isc，其中癸酸盐（C10:0）是最有效的水溶性脂肪酸。这种脂肪酸抑制了一种氯离子电流，该电流在基底外侧膜去极化后由浆膜向黏膜方向的氯离子梯度驱动穿过顶端膜。脂肪酸的第二个作用位点似乎是基底外侧膜。在用离子载体制霉菌素使顶端膜通透后，黏膜向浆膜方向的钾离子梯度诱导出一种钾离子电流，该电流也被癸酸盐抑制。这些结果表明，卡巴胆碱不仅作为一种促分泌剂起作用，同时还通过增加细胞内脂肪酸浓度引发下调作用，这是一种限制氯离子分泌的机制。
