RHEAULT, M.R.; O’DONNELL, M.J.; DONLY, B.C.; McMaster University; McMaster University; Agriculture and Agri-Food Canada: Renal and Extrarenal Transport of Organic Anions and Organic Cations by Insects; A Comparison with Vertebrates.

A wide range of structurally unrelated organic cations (OCs) and organic anions (OAs) are transported by renal and extrarenal tissues of vertebrates and invertebrates. In all insects studied to date, the Malpighian (renal) tubules (MTs) actively excrete OCs and OAs. Such mechanisms are of likely importance in insecticide resistance and in explaining the ability of some insects to feed on plants containing toxins such as alkaloids. We have examined OA and OC transport mechanisms in several insects through a combination of three approaches: 1) analysis of transepithelial and basolateral fluxes of fluorescent or radiolabelled OCs and OAs; 2) development of non-invasive electrophysiological techniques for temporal and spatial analysis of OC or OA transport; 3) cloning, sequencing and tissue expression of genes for potential xenobiotic transport proteins such as p-glycoprotein. Our results allow comparisons with vertebrate mechanisms for OA and OC transport. It appears that as in vertebrate systems excretion of OCs and OAs involves multiple transporters with overlapping substrate specificities. We have evidence for 5 putative genes encoding for p-glycoprotein-like transporters. MT transport of the prototypical OC substrate tetraethylammonium (TEA) is saturable, electrogenic and inhibited by blockers of both vertebrate OCTs and p-glycoproteins. Analysis of extra-renal epithelia reveal TEA transport by the midgut. Transport of OAs (PAH, salicylate, fluorescein) by the MTs is Na-dependent, but does not involve OA/α-keto acid exchange, as in vertebrates. The hindgut also transports the OA salicylate.