Matsuda T, Shimizu I, Baba A
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
Eur J Pharmacol. 1991 Nov 12;204(3):257-63. doi: 10.1016/0014-2999(91)90850-p.
Treatment of rat brain slices with veratrine and monensin decreased (Na+ + K+)-ATPase activity in the membranes in a dose-dependent manner. The effect of monensin, like that of veratrine, was accompanied by a decrease of maximal binding sites for ouabain. The inhibitory effect of monensin on the enzyme activity was dependent on external Ca2+ at low concentrations, but not at a high concentration. The decreased enzyme activity induced by monensin was restored by subsequent incubation of the slices in a Ca(2+)-free medium containing 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM), a chelator of intracellular Ca2+. The effect of monensin at a low concentration on enzyme activity was antagonized by amiloride (1 mM), bepridil (5 microM), quinacrine (30 microM) or verapamil (30 microM), but not by nifedipine (1 microM) or omega-conotoxin (1 microM). Furthermore, the inhibitory effect of monensin at a high concentration under Ca(2+)-free conditions was blocked by BAPTA-AM (30 microM) and by bepridil (100 microM) or diazepam (500 microM), inhibitors of mitochondrial Na(+)-Ca2+ exchange. Inhibitors of calmodulin, protein kinase C, phospholipase A2 and calpain did not affect the monensin-induced decrease of enzyme activity. Dithiothreitol (10 mM) blocked the effect of monensin on enzyme activity but did not affect the ionophore-induced influx of Ca2+ in the slices.
用藜芦碱和莫能菌素处理大鼠脑片，可使膜中（Na⁺ + K⁺）-ATP酶活性呈剂量依赖性降低。莫能菌素的作用与藜芦碱类似，同时伴有哇巴因最大结合位点的减少。莫能菌素对酶活性的抑制作用在低浓度时依赖于细胞外Ca²⁺，但在高浓度时则不依赖。莫能菌素诱导的酶活性降低可通过随后将脑片在含有1,2-双（2-氨基苯氧基）乙烷-N,N,N',N'-四乙酸四乙酰甲酯（BAPTA-AM，一种细胞内Ca²⁺螯合剂）的无Ca²⁺培养基中孵育而恢复。低浓度莫能菌素对酶活性的作用可被阿米洛利（1 mM）、苄普地尔（5 μM）、奎纳克林（30 μM）或维拉帕米（30 μM）拮抗，但不受硝苯地平（1 μM）或ω-芋螺毒素（1 μM）影响。此外，在无Ca²⁺条件下高浓度莫能菌素的抑制作用可被BAPTA-AM（30 μM）以及线粒体Na⁺-Ca²⁺交换抑制剂苄普地尔（100 μM）或地西泮（500 μM）阻断。钙调蛋白、蛋白激酶C、磷脂酶A2和钙蛋白酶的抑制剂不影响莫能菌素诱导的酶活性降低。二硫苏糖醇（10 mM）阻断了莫能菌素对酶活性的作用，但不影响离子载体诱导的脑片中Ca²⁺内流。
