QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hazel, M. H. Articles by O'Donnell, M. J. Search for Related Content PubMed PubMed Citation Articles by Hazel, M. H. Articles by O'Donnell, M. J.

Amino acids modulate ion transport and fluid secretion by insect Malpighian tubules

Matthew H. Hazel¹, Juan P. Ianowski¹, Robert J. Christensen¹, Simon H. P. Maddrell² and Michael J. O'Donnell^1,*

¹ Dept of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4KI, Canada
² Dept of Zoology, Downing Street, Cambridge, CB2 3EJ, UK

View larger version (28K): [in a new window]   Fig. 1. Effects of amino acids on secretion rates of Drosophila melanogaster tubules. The continuous-exposure protocol was used (see Materials and methods). Amino acids were tested at 20 mmol l-1 except for threonine and tyrosine, which were tested at 10 mmol l-1 and 0.5 mmol l-1, respectively, due to their lower solubility in Drosophila saline. For each amino acid, a corresponding set of controls was run in amino-acid-free saline. Each bar represents the mean secretion rate (+S.E.M.) as a percentage of the corresponding control mean. N=8-16 tubules for each amino acid and corresponding control group. Asterisks represent significant (P<0.05) increases or decreases in secretion rate relative to the controls. The inset shows a dose—response curve (mean ± S.E.M.) for glutamine.

View larger version (15K): [in a new window]   Fig. 2. Time course of the effects of glutamine and cysteine on secretion rates of Drosophila tubules. Values are means ± S.E.M. Filled circles represent control tubules in amino-acid-free Drosophila saline (N=7), filled squares represent tubules exposed to 20 mmol l-1 cysteine at t=40 min (N=12), and open circles represent tubules exposed to cysteine at t=40 min, and then to both 20 mmol l-1 cysteine and 20 mmol l-1 glutamine at t=80 min (N=3).

View larger version (16K): [in a new window]   Fig. 3. Time course of the effects of glutamine on secretion rates of 4th instar Rhodnius Malpighian tubules. The experiment represents a typical rescue protocol. Values are means ± S.E.M. All tubules were started in amino-acid-free control saline and were stimulated with 5-HT at t=0 min. The time of glutamine (20 mmol l-1) addition is indicated by the arrow. Filled circles indicate tubules exposed to the glutamine (N=8), and open circles indicate control tubules (N=8). Asterisks indicate significant differences from the value for the same group at t=75 min.

View larger version (34K): [in a new window]   Fig. 4. Graph summarizing the results of rescue experiments for Rhodnius prolixus. All amino acids were tested at 20 mmol l-1 except threonine, which was tested at 10 mmol l-1 due to its solubility. Each bar represents the mean secretion rate (+ S.E.M.) as a percentage of the corresponding control mean. N=7-9 tubules for each amino acid and corresponding control group. The broken line indicates the control rate (100%). Asterisks represent significant (P<0.05) increases or decreases in secretion rate relative to the controls. Tyrosine was not tested because its low solubility did not permit preparation of an appropriate stock solution at 10x the final concentration. The insets show dose—response curves for stimulation by glutamine and inhibition by arginine and lysine. Values are means ± S.E.M. (N=17-13 tubules for each amino acid and corresponding control group).

View larger version (15K): [in a new window]   Fig. 5. Secretion rates of 4th instar Rhodnius Malpighian tubules set up using the pre-incubation protocol. Values are means ± S.E.M. (N=8 for both groups). The experimental tubules (filled circles) were preincubated for 2.5 h in 20 mmol l-1 glutamine, whereas the control tubules (open circles) were pre-incubated for 2.5 h in amino-acid-free control saline. All tubules were then transferred to amino-acid-free control saline and stimulated with 5-hydroxytryptamine (5-HT) at the time indicated by the arrow.

View larger version (24K): [in a new window]   Fig. 6. Graph summarizing the results of pre-incubation experiments for Rhodnius tubules. All amino acids were tested at 20 mmol l-1 except for threonine (10 mmol l-1) and tyrosine (0.5 mmol l-1). Each bar represents the mean secretion rate (+ S.E.M.) as a percentage of the corresponding control mean. The broken line indicates the control rate (100%). N=7-16 tubules for each amino acid and corresponding control group. Asterisks indicate significant (P<0.05) increases or decreases in secretion rate relative to controls. The inset shows the extent to which the inhibition produced by cysteine could be reversed by subsequent addition of 20 mmol l-1 glutamine.

View larger version (22K): [in a new window]   Fig. 7. Graph summarizing the results of pre-incubation experiments for Drosophila tubules. All amino acids were used at 20 mmol l-1 except for threonine (10 mmol l-1) and tyrosine (0.5 mmol l-1). Each bar represents the mean secretion rate (+ S.E.M.) as a percentage of the corresponding control mean. The broken line indicates the control rate (100%). N=8-16 tubules for each amino acid and corresponding control group. Asterisks represent significant (P<0.05) increases or decreases in secretion rate relative to controls.

View larger version (16K): [in a new window]   Fig. 8. Secretion rate and secreted fluid Na+ and K+ concentrations for 4th instar Rhodnius Malpighian tubules set up in a rescue experiment. Values are means ± S.E.M. (N=8 tubules for each group). Filled circles represent tubules rescued with 20 mmol l-1 glutamine at t=60 min (indicated by the arrow), and open circles represent control tubules. Asterisks represent significant (P<0.05) increases or decreases relative to controls.

View larger version (13K): [in a new window]   Fig. 9. Secretion rate and secreted fluid Na+ and K+ concentrations for 4th instar Rhodnius Malpighian tubules set up in a pre-incubation experiment. Values are means ± S.E.M. (N=8 tubules for each group). Filled circles represent tubules pre-incubated with 20 mmol l-1 glutamine, and open circles represent control tubules pre-incubated in amino-acid-free saline. Asterisks represent significant (P<0.05) increases or decreases relative to controls. Tubules were stimulated with 5-hydroxytryptamine (5-HT) at t=0 min.

View larger version (14K): [in a new window]   Fig. 10. Secretion rate and secreted fluid pH for 4th instar Rhodnius tubules pre-incubated for 2 h in 20 mol l-1 glutamine (filled circles), 20 mol l-1 arginine (open circles) or amino-acid-free saline (filled squares). Values are means ± S.E.M. (N=8 tubules for each group). Asterisks represent significant (P<0.05) increases or decreases relative to controls.