School of Life Sciences, University of Sussex, Falmer, Brighton, United Kingdom.
Department of Bioscience, Swansea University, Swansea, Singleton park, Wales, United Kingdom.
PLoS One. 2019 Oct 8;14(10):e0223569. doi: 10.1371/journal.pone.0223569. eCollection 2019.
Extrusion of xenobiotics is essential for allowing animals to remove toxic substances present in their diet or generated as a biproduct of their metabolism. By transporting a wide range of potentially noxious substrates, active transporters of the ABC transporter family play an important role in xenobiotic extrusion. One such class of transporters are the multidrug resistance P-glycoprotein transporters. Here, we investigated P-glycoprotein transport in the Malpighian tubules of the desert locust (Schistocerca gregaria), a species whose diet includes plants that contain toxic secondary metabolites. To this end, we studied transporter physiology using a modified Ramsay assay in which ex vivo Malpighian tubules are incubated in different solutions containing the P-glycoprotein substrate dye rhodamine B in combination with different concentrations of the P-glycoprotein inhibitor verapamil. To determine the quantity of the P-glycoprotein substrate extruded we developed a simple and cheap method as an alternative to liquid chromatography-mass spectrometry, radiolabelled alkaloids or confocal microscopy. Our evidence shows that: (i) the Malpighian tubules contain a P-glycoprotein; (ii) tubule surface area is positively correlated with the tubule fluid secretion rate; and (iii) as the fluid secretion rate increases so too does the net extrusion of rhodamine B. We were able to quantify precisely the relationships between the fluid secretion, surface area, and net extrusion. We interpret these results in the context of the life history and foraging ecology of desert locusts. We argue that P-glycoproteins contribute to the removal of xenobiotic substances from the haemolymph, thereby enabling gregarious desert locusts to maintain toxicity through the ingestion of toxic plants without suffering the deleterious effects themselves.
外排异生物对于动物来说至关重要，因为这可以让它们清除饮食中存在的有毒物质或作为新陈代谢副产物产生的有害物质。ABC 转运蛋白家族的主动转运蛋白通过转运广泛的潜在有害物质，在异生物外排中发挥着重要作用。多药耐药 P-糖蛋白转运蛋白就是这样一类转运蛋白。在这里，我们研究了沙漠蝗（Schistocerca gregaria）的马尔皮基氏小管中的 P-糖蛋白转运，这种物种的饮食包括含有有毒次生代谢物的植物。为此，我们使用改良的 Ramsay 测定法研究了转运蛋白生理学，其中离体的马尔皮基氏小管在不同的溶液中孵育，这些溶液含有 P-糖蛋白底物染料罗丹明 B，并结合不同浓度的 P-糖蛋白抑制剂维拉帕米。为了确定外排的 P-糖蛋白底物的量，我们开发了一种简单且廉价的方法，作为液相色谱-质谱、放射性标记生物碱或共聚焦显微镜的替代方法。我们的证据表明：（i） 马尔皮基氏小管含有 P-糖蛋白；（ii） 小管表面积与小管液分泌率呈正相关；（iii） 随着分泌率的增加，罗丹明 B 的净外排也增加。我们能够准确地量化液分泌、表面积和净外排之间的关系。我们根据沙漠蝗的生活史和觅食生态学来解释这些结果。我们认为 P-糖蛋白有助于从血液中去除异生物物质，从而使群居的沙漠蝗能够通过摄入有毒植物来维持毒性，而不会对自身造成有害影响。
