Neufeld Douglas S G, Kauffman Ross, Kurtz Zachary
Department of Biology, Eastern Mennonite University, Harrisonburg, VA 22802, USA.
J Exp Biol. 2005 Jun;208(Pt 12):2227-36. doi: 10.1242/jeb.01617.
We demonstrate the presence of an efficient, multispecific transport system for excretion of organic anions in the Malpighian tubules of the cricket Acheta domesticus using fluorescein (FL) as a model substrate. Malpighian tubules rapidly accumulated FL via a high affinity process (Km = 7.75 micromol l(-1)); uptake was completely eliminated by the prototypical organic anion transport inhibitor probenecid (1 mmol l(-1)), but not by p-aminohippuric acid (3 mmol l(-1)). FL uptake was inhibited by monocarboxylic acids at a high concentration (3 mmol l(-1)), and inhibition was more effective with an increase in the carbon chain of the monocarboxylic acid (37% inhibition by 5-carbon valeric acid, and 89% inhibition by 7-carbon caprylic acid). Likewise, tests using a series of aliphatic glutathione conjugates indicated that only the compound with the longest side-chain (decyl-glutathione) significantly inhibited FL uptake (81% inhibition). FL uptake was inhibited by a number of xenobiotics, including a plant alkaloid (quinine), herbicides (2,4-dichlorophenoxyacetic acid and 4-(2,4-dichlorophenoxy)-butyric acid), and the insecticide metabolites malathion monocarboxylic acid (MMA) and 3-phenoxybenzoic acid (PBA), suggesting that this transport system plays an active role in excretion of xenobiotics from Acheta by Malpighian tubules. HPLC quantification of MMA and PBA accumulation into Malpighian tubules verified that MMA accumulation was via a mediated transport process, but suggested that PBA accumulation was by nonspecific binding. The presence of a transport system in Malpighian tubules that handles at least one pesticide metabolite (MMA) suggests that transport processes could be a mechanism conferring resistance to xenobiotic exposure in insects.
我们以荧光素（FL）作为模型底物，证明了家蟋蟀马氏管中存在一种高效的多特异性有机阴离子排泄转运系统。马氏管通过高亲和力过程（Km = 7.75 μmol l⁻¹）迅速积累FL；原型有机阴离子转运抑制剂丙磺舒（1 mmol l⁻¹）可完全消除摄取，但对氨基马尿酸（3 mmol l⁻¹）则不能。高浓度（3 mmol l⁻¹）的一元羧酸可抑制FL摄取，且随着一元羧酸碳链长度增加抑制作用更有效（戊酸抑制37%，辛酸抑制89%）。同样，使用一系列脂肪族谷胱甘肽缀合物的测试表明，只有侧链最长的化合物（癸基谷胱甘肽）能显著抑制FL摄取（抑制81%）。多种外源性物质可抑制FL摄取，包括植物生物碱（奎宁）、除草剂（2,4 - 二氯苯氧乙酸和4 - (2,4 - 二氯苯氧基)丁酸）以及杀虫剂代谢物马拉硫磷单羧酸（MMA）和3 - 苯氧基苯甲酸（PBA），这表明该转运系统在马氏管将外源性物质从家蟋蟀体内排泄过程中发挥着积极作用。对马氏管中MMA和PBA积累的HPLC定量分析证实，MMA积累是通过介导的转运过程，但表明PBA积累是通过非特异性结合。马氏管中存在处理至少一种农药代谢物（MMA）的转运系统，这表明转运过程可能是昆虫对外源性物质暴露产生抗性的一种机制。
