Cellular and molecular mechanisms of ion transport by the insect excretory system

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Insects are the most abundant animal group, representing roughly 95% of the known animal species. Although insects appear to be most abundant in the tropics, they have successfully exploited almost every ecological niche of the terrestrial environment including some that lead to major economic, agricultural, or health crisis. In order to deal with the vast number of environmental stresses that these various ecological niches have imposed, insects have evolved sophisticated systems for the control of osmotic and ionic balance that allow most species to regulate their haemolymph composition and volume within a narrow range. The amazing evolutionary adaptations that allow insect to regulate their osmotic state have puzzled researchers for decades. Through my research I will further our understanding of osmoregulation and excretion in insects and the enormous diversity that this group has evolved. In the current grant proposal, we study osmoregulation in the triatomine bloodsucker Rhodnius prolixus, a vector for Chagas disease. Each blood meal loads R. prolixus with excess water and NaCl imposing severe osmotic stress, which the insect resolves with a massive diuretic process. Diuresis is carried out by the excretory system-the Malpighian tubules and crop-which forms urine by active ion transport and osmotically obliged water flow. Diuretic hormones stimulate both the crop and the Malpighian tubules to transport of ions at very high rates. Fully stimulated tubules transport fluid at rates equivalent to each cell exchanging their whole volume every 10 s and their intracellular Na+ and Cl- content in 5 s. This requires highly efficient regulatory mechanisms to ensure ion and fluid homeostasis during postprandial diuresis. In this grant HQP under my supervision at the undergraduate, graduate, and postdoctoral levels will study the hormonal signals that coordinate the function of the crop and Malpighian tubules and the intracellular machinery needed to preserve homeostasis. In addition, my research project will advance our understanding of fundamental mechanisms of epithelial physiology. One of the most interesting questions on epithelial physiology is the nature of the intracellular crosstalk mechanisms which regulate ion transporters to maintain transepithelial transport while defending cytosolic composition. Insect excretory epithelia are ideal models to study these mechanisms, that have remain elusive so far. The knowledge generated through this research will contribute to improve the life of Canadians by facilitating the rational development of cost-effective, insect specific and environmentally benign pest control measures and by providing new knowledge that may help better understand health conditions. Funding from this grant will support the training of HQP on molecular biology, advanced electrophysiology and pharmacology that will prepare them for careers in academia and in industry.