Ozaki H, Kojima T, Moriyama T, Karaki H, Urakawa N, Kohama K, Nonomura Y
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Japan.
J Pharmacol Exp Ther. 1987 Oct;243(1):370-7.
The relaxant action of amiloride was investigated in the smooth muscles of guinea pig taenia ceci and chicken gizzard. Amiloride inhibited the contractions induced by high K+ (45.4 mM) and carbachol (10 microM) in the taenia with the concentrations needed to induce 50% inhibition (IC50) of approximately 41 microM. A prolonged incubation period (greater than 1 hr) was necessary to obtain the full inhibition of these contractions. The taenia gradually accumulated amiloride and the tissue/medium ratio exceeded 2.0 after a 120-min incubation period. Amiloride had no effect on the high K+-stimulated 45Ca++ uptake or the ATP content of the taenia. Amiloride inhibited the Ca++-induced contraction of the saponin-treated taenia with an IC50 of 186 microM. Amiloride (10-1000 microM) also inhibited superprecipitation and Mg++-adenosine triphosphatase activity of the gizzard native actomyosin as well as the phosphorylation of myosin light chain. The inhibition of the phosphorylation was antagonized competitively by ATP. Amiloride (1 mM) had no effect on the dephosphorylation of myosin light chain upon removal of Ca++ from reaction medium. Amiloride, at concentrations up to 1 mM, had not effect on calmodulin activity as monitored by the Ca++-calmodulin-activated erythrocyte membrane (Ca++ + Mg++)-adenosine triphosphatase and phosphodiesterase activities. In contrast to this, trifluoperazine inhibited the calmodulin activity at the concentration needed to inhibit the Ca++-induced contraction of the permeabilized taenia and the superprecipitation and the phosphorylation of myosin light chain of gizzard. We conclude that amiloride, unlike trifluoperazine, may inhibit directly the myosin light chain kinase activity to induce muscle relaxation.
在豚鼠盲肠带和鸡砂囊的平滑肌中研究了阿米洛利的松弛作用。阿米洛利抑制了高钾（45.4 mM）和卡巴胆碱（10 μM）在盲肠带中诱导的收缩，诱导50%抑制（IC50）所需的浓度约为41 μM。需要较长的孵育时间（大于1小时）才能完全抑制这些收缩。盲肠带逐渐积累阿米洛利，孵育120分钟后组织/培养基比值超过2.0。阿米洛利对高钾刺激的45Ca++摄取或盲肠带的ATP含量没有影响。阿米洛利抑制皂素处理的盲肠带中Ca++诱导的收缩，IC50为186 μM。阿米洛利（10 - 1000 μM）还抑制了砂囊天然肌动球蛋白的超沉淀和Mg++ - 三磷酸腺苷酶活性以及肌球蛋白轻链的磷酸化。磷酸化的抑制被ATP竞争性拮抗。当从反应介质中去除Ca++时，1 mM的阿米洛利对肌球蛋白轻链的去磷酸化没有影响。浓度高达1 mM的阿米洛利对通过Ca++ - 钙调蛋白激活的红细胞膜（Ca++ + Mg++） - 三磷酸腺苷酶和磷酸二酯酶活性监测的钙调蛋白活性没有影响。与此形成对比的是，三氟拉嗪在抑制通透化盲肠带的Ca++诱导收缩、砂囊肌球蛋白轻链的超沉淀和磷酸化所需的浓度下抑制钙调蛋白活性。我们得出结论，与三氟拉嗪不同，阿米洛利可能直接抑制肌球蛋白轻链激酶活性以诱导肌肉松弛。
