Frederiksen O
J Physiol. 1983 Feb;335:75-88. doi: 10.1113/jphysiol.1983.sp014520.
The effects of the Na+-channel-blocking diuretic agent amiloride were assessed in the rabbit gall-bladder epithelium, a low-resistance epithelium with an isosmotic, coupled NaCl transport mechanism. Amiloride caused a rapid, reversible, and dose-dependent decrease in fluid absorption when applied from the mucosal side in concentrations between 8.8 X 10(-5) and 1.76 X 10(-3) M. These concentrations were without effect from the serosal side, suggesting an action of amiloride in the luminal cell membrane as in high-resistance epithelia. Amiloride did not affect the epithelial resistance or the passive serosa-to-mucosa Na+ flux, while net Na+ and water reabsorption were inhibited in parallel. Thus, amiloride did not affect the paracellular tight junction pathway, but inhibited a transcellular, coupled salt and water transport mechanism. The kinetics of the amiloride effect were of a Michaelis-Menten type. The dose of amiloride giving 50% inhibition of fluid absorption (ID50) was 4 X 10(-4) M, a value about three orders of magnitude higher than in high-resistance, Na+-retaining epithelia. The percentage inhibitory effect at each concentration of amiloride increased with increasing rate of spontaneous (control) fluid transport, reaching maximal responses fitting a Michaelis-Menten kinetic with an ID50 of 1.5 X 10(-4) M. No effects of changing the extracellular Na+ concentration between 51 and 145 mequiv/l on the maximal inhibitory effect of amiloride on Na+ and water reabsorption were observed. This suggests a non-competitive type of action of amiloride on a Na+-dependent isosmotic fluid transport mechanism. Removal of mucosal Ca2+ did not alter the effect of amiloride. The implications of these findings are discussed in relation to concepts concerning the mechanism of isosmotic salt and water transport. The data are compatible with the concept that amiloride interferes with a Na+-dependent formation and transcellular transport of isosmotic fluid volumes in a sequestered compartment in the epithelial cells.
在兔胆囊上皮（一种具有等渗性、耦联的氯化钠转运机制的低电阻上皮）中评估了钠通道阻滞剂阿米洛利的作用。当以8.8×10⁻⁵至1.76×10⁻³M的浓度从黏膜侧施加时，阿米洛利导致液体吸收迅速、可逆且呈剂量依赖性降低。这些浓度从浆膜侧施加则无作用，提示阿米洛利在腔面膜中的作用与在高电阻上皮中一样。阿米洛利不影响上皮电阻或被动的从浆膜到黏膜的钠通量，而净钠和水重吸收则同时受到抑制。因此，阿米洛利不影响细胞旁紧密连接途径，而是抑制了一种跨细胞的、耦联的盐和水转运机制。阿米洛利作用的动力学符合米氏类型。产生50%液体吸收抑制作用的阿米洛利剂量（ID50）为4×10⁻⁴M，该值比在高电阻、保钠上皮中高约三个数量级。在每个阿米洛利浓度下的抑制作用百分比随自发（对照）液体转运速率的增加而增加，达到符合米氏动力学的最大反应，ID50为1.5×10⁻⁴M。未观察到细胞外钠浓度在51至145毫当量/升之间变化对阿米洛利对钠和水重吸收的最大抑制作用有影响。这提示阿米洛利对钠依赖性等渗液体转运机制的作用为非竞争性类型。去除黏膜钙不改变阿米洛利的作用。结合关于等渗盐和水转运机制的概念讨论了这些发现的意义。数据与以下概念相符：阿米洛利干扰上皮细胞中一个隔离区室中钠依赖性等渗液体体积的形成和跨细胞转运。
