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First published online June 6, 2005
Journal of Experimental Biology 208, 2227-2236 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01617

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Specificity of the fluorescein transport process in Malpighian tubules of the cricket Acheta domesticus

Douglas S. G. Neufeld^1,*, Ross Kauffman² and Zachary Kurtz¹

¹ Department of Biology, Eastern Mennonite University, Harrisonburg, VA 22802, USA
² Ohio State University, School of Public Health, Columbus, OH 43210, USA

^* Author for correspondence (e-mail: neufeldd{at}emu.edu)

Accepted 23 March 2005

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 (K_m=7.75 µmol 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.

Key words: Malpighian tubules, fluorescein, organic anion transport, Acheta domesticus, pesticide

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