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First published online June 29, 2007
Journal of Experimental Biology 210, 2464-2471 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003152

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Effects of chronic exposure to dietary salicylate on elimination and renal excretion of salicylate by Drosophila melanogaster larvae

Esau Ruiz-Sanchez^* and Michael J. O'Donnell

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

View larger version (10K): [in this window] [in a new window]   Fig. 1. Salicylate levels in the haemolymph of third instar larvae fed on a salicylate-enriched diet. (A) Levels of salicylate in the haemolymph of larvae fed on a 20 mmol l–1 salicylate-enriched diet for different periods. (B) Levels of salicylate in the haemolymph of larvae fed for 24 h on diets with different concentrations of salicylate. Each point represents the mean ± s.e.m. of 25–50 samples. The curve was fitted to the Michaelis–Menten equation by non-linear regression analysis.

View larger version (10K): [in this window] [in a new window]   Fig. 2. Kinetics of salicylate elimination from the haemolymph of third instar D. melanogaster larvae. Haemolymph salicylate concentration was measured (0–6 h) after transfer of larvae that had been fed for 24 h on a 20 mmol l–1 salicylate-enriched diet to a salicylate-free diet. Solid and broken lines indicate the control and experimental group, respectively. Experimental larvae were raised for 10 days on a 10 mmol l–1 salicylate-enriched diet and subsequently transferred for 15 h to a salicylate-free diet, whereas control larvae were raised on a salicylate-free diet (inset). Each point represents the mean (± s.e.m.) of 25–50 samples. The curve was fitted to a one-compartment model by non-linear regression analysis.

View larger version (17K): [in this window] [in a new window]   Fig. 3. Effects of chronic exposure of D. melanogaster larvae to dietary salicylate on (A) fluid secretion rate, (B) salicylate concentration in the secreted fluid and (C) transepithelial flux of salicylate across the main segment of isolated Malpighian tubules set up in the Ramsay assay. Each point represents the mean ± s.e.m. of 7–10 tubules. Solid and broken lines indicate the control and experimental group, respectively. Experimental larvae were raised for 10 days on a 10 mmol l–1 salicylate-enriched diet. Control larvae were raised on a salicylate-free diet.

View larger version (8K): [in this window] [in a new window]   Fig. 4. Effects of Na+-free bathing saline on (A) fluid secretion rate and (B) transepithelial flux of salicylate across the main segment of isolated Malpighian tubules set up in the Ramsay assay. Malpighian tubules were bathed in control saline (solid bars) or Na+-free saline (hatched bars) containing 50 µmol l–1 salicylate. Experimental larvae were raised for 10 days on a 10 mmol l–1 salicylate-enriched diet. Control larvae were raised on a salicylate-free diet. Secreted fluid droplets were collected after 40 min. Values are means ± s.e.m. (N=6–9 tubules). Asterisks indicate significant differences between control and experimental groups (*P<0.05, **P<0.01; t-test, N=6–8).

View larger version (4K): [in this window] [in a new window]   Fig. 5. Effects of 1 mmol l–1 cAMP on the rate of fluid secretion by the main segment of isolated Malpighian tubules set up in the Ramsay assay. The first secreted droplet was collected at 30 min (solid bars) and the second secreted droplet (hatched bars) was collected 30 min after adding cAMP. Experimental larvae were raised for 10 days on a 10 mmol l–1 salicylate-enriched diet. Control larvae were raised on a salicylate-free diet. Values are means ± s.e.m. (N=8–10 tubules). Asterisks indicate significant differences in fluid secretion rate before and after adding cAMP (**P<0.01, ***P<0.001; paired t-test, N=8–10).

View larger version (5K): [in this window] [in a new window]   Fig. 6. Effects of 10 µmol l–1 leucokinin I on the rate of fluid secretion by the main segment of isolated Malpighian tubules set up in the Ramsay assay. The first secreted droplet was collected at 30 min (solid bars) and the second secreted droplet (hatched bars) was collected 30 min after adding leucokinin I. Experimental larvae were raised for 10 days on a 10 mmol l–1 salicylate-enriched diet. Control larvae were raised on a salicylate-free diet. Values are means ± s.e.m. (N=7–9 tubules). Asterisks indicate significant differences in fluid secretion rate before and after adding leucokinin are indicated (***P<0.001; paired t-test, N=7–9).

View larger version (5K): [in this window] [in a new window]   Fig. 7. Effects of chronic exposure of D. melanogaster larvae to dietary salicylate on salicylate influx across three segments of the isolated gut. Fluxes were measured using the scanning ion electrode technique as described in the Materials and methods. Gut segments were bathed in 30 mmol l–1 Cl– saline containing 100 µmol l–1 salicylate. Flux for each segment of each larva was calculated as the mean value for three sites separated by 480 µm for the midgut and 200 µm for the ileum and rectum. Solid and hatched bars indicate mean ± s.e.m. for 4–5 larvae in the control and experimental group, respectively. Experimental larvae were raised for 10 days on a 10 mmol l–1 salicylate-enriched diet. Control larvae were raised on a salicylate-free diet. No significant differences between groups were observed (P>0.05).