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First published online February 4, 2005
Journal of Experimental Biology 208, 603-610 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01422

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Analysis of Na⁺, Cl^-, K⁺, H⁺ and NH₄⁺ concentration gradients adjacent to the surface of anal papillae of the mosquito Aedes aegypti: application of self-referencing ion-selective microelectrodes

Andrew Donini^* and Michael J. O'Donnell

Department of Biology, McMaster University, Life Sciences Building, 1280 Main Street West, Hamilton, Ontario, Canada, L8S 4K1

^* Author for correspondence (e-mail: doninia{at}mcmaster.ca)

Accepted 30 November 2004

Ion concentration gradients adjacent to the surface of the anal papillae of larvae of the mosquito Aedes aegypti were measured using self-referencing ion-selective microelectrodes. The gradients were used to calculate estimates of ion fluxes into and out of the papillae. There was a net influx of Na⁺, Cl^- and K⁺ from the bathing medium and a net efflux of acid and NH₄⁺. No Ca²⁺ gradients were detectable. Na⁺ and Cl^- influx occurred against a concentration gradient suggesting active transport. Although Na⁺, Cl^- and NH₄⁺ gradients were uniform along the length of the papillae, the proximal regions of the papillae in vivo revealed significantly higher H⁺ and K⁺ gradients compared with distal regions. The calculated ion fluxes at the papillae are sufficient for complete Na⁺, K⁺ and Cl^- haemolymph replacement in 4 h with external ion concentrations of 5 mmol l^-1. Ion gradients were also detected adjacent to the surface of isolated papillae; however, Na⁺ and H⁺ gradients were higher, and Cl^- gradients were lower relative to papillae in vivo. The results support previous findings that the anal papillae of mosquito larvae are important structures for ion regulation, and suggest that these structures may be used for the excretion of nitrogenous waste.

Key words: anal papillae, mosquito, Aedes aegypti, ion transport, self-referencing ion selective microelectrode

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