Physiological screening for target site insensitivity and localization of Na(+)/K(+)-ATPase in cardenolide-adapted Lepidoptera.
Physiological screening for target site insensitivity and localization of Na(+)/K(+)-ATPase in cardenolide-adapted Lepidoptera.
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DOI：
10.1016/j.jinsphys.2011.12.012
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发表时间：
2012-05
影响因子：
2.2
通讯作者：
Georg Petschenka;Julia Offe;S. Dobler
中科院分区：
文献类型：
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作者：
Georg Petschenka;Julia Offe;S. Dobler
Cardenolide是一种有毒的植物化合物，它能特异性地抑制Na+/K+-ATPase，这是一种动物酶，在许多生理过程中都是必不可少的，如动作电位的产生。几种适应环境的昆虫以含有卡地奈德的植物为食，将这些毒素隔离起来，以自卫。其中一些昆虫具有Na+/K+-ATPase，对Cardenolide的敏感性降低(靶点不敏感)。在本研究中，我们用体外酶试验筛选了五种取食于含有卡地龙内酯的植物的弓形虫对卡地那内酯的靶点不敏感。将得到的Na+/K+-ATPase的剂量反应曲线与帝王蝶(Danaus Plexippus)不敏感的Na+/K+-ATPase进行了比较。所有供试物种的Na+/K+-ATPase对哇巴因高度敏感，哇巴因是一种在实验室研究中使用最广泛的水溶性卡地奈德。然而，我们在两个北极科物种的血淋巴中检测到了大量的Cardenolide。用免疫组织化学和免疫印迹方法对粘虫幼虫和毛虫体内的Na+/K+-ATPase进行了定位。这两种技术都显示该酶在神经组织中有很强的表达，而在其他被测试的组织中表达很弱，甚至没有表达。我们得出的结论是，与目标位置不敏感不同，被调查的牛膝属物种使用了不同的策略来耐受卡登内酯。最有可能的是，神经组织周围的神经膜起到了屏障的作用，阻止了腰果内酯到达腹神经索的Na+/K+-ATPase。
Cardenolides are toxic plant compounds which specifically inhibit Na+/K+-ATPase, an animal enzyme which is essential for many physiological processes, such as the generation of action potentials. Several adapted insects feeding on cardenolide-containing plants sequester these toxins for their own defence. Some of these insects were shown to possess Na+/K+-ATPases with a reduced sensitivity towards cardenolides (target site insensitivity). In the present study we screened five species of arctiid moths feeding on cardenolide-containing plants for target site insensitivity towards cardenolides using an in vitro enzyme assay. The derived dose response curves of the respective Na+/K+-ATPases were compared to the insensitive Na+/K+-ATPase of the monarch butterfly (Danaus plexippus). Na+/K+-ATPases of all arctiid species tested were highly sensitive to ouabain, a water-soluble cardenolide which is most widely used in laboratory studies. Nevertheless, we detected substantial amounts of cardenolides in the haemolymph of two of the arctiid species. In caterpillars of the sequestering arctiid Empyreuma pugione and of D. plexippus we localized Na+/K+-ATPase by immunohistochemistry and western blot (in D. plexippus). Both techniques revealed strong expression of the enzyme in the nervous tissue and indicated weak expression or even absence in other tissues tested. We conclude that instead of target site insensitivity the investigated arctiid species use a different strategy to tolerate cardenolides. Most plausibly, the perineurium surrounding the nervous tissue functions as a barrier which prevents cardenolides from reaching Na+/K+-ATPase in the ventral nerve cord.