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Sulphonylurea sensitivity and enriched expression implicate inward rectifier K+ channels in Drosophila melanogaster
Jennifer M Evans1, Adrian K Allan, Shireen A Davies
1Division of Molecular Genetics, Faculty of Biomedical and Life Sciences, University of Glasgow, UK.
The Journal of Experimental Biology
|September 20, 2005
Summary
Insect renal tubules use inward rectifier potassium channels for fluid transport. Inhibitors like glibenclamide block this process, revealing new roles for these channels in secretion and solute transport.
Area of Science:
- Physiology
- Molecular Biology
- Pharmacology
Background:
- Insect Malpighian (renal) tubules exhibit high fluid transport rates.
- Efficient potassium transport is crucial for tubule function, requiring robust basolateral entry routes.
- Microarray analysis revealed high abundance of inward rectifier potassium (K+) channel genes (ir, irk2, irk3) in Drosophila tubules.
Purpose of the Study:
- To investigate the role of inward rectifier potassium channels in insect renal tubule fluid secretion.
- To characterize the pharmacological properties of these channels using selective inhibitors.
- To explore potential interactions of glibenclamide with other tubule transport systems.
Main Methods:
- Quantitative RT-PCR and in situ hybridization to confirm gene expression and localization of inward rectifier channels.
- Assessment of fluid secretion using selective inward rectifier channel inhibitors (sulfonylureas, minoxidil, diazoxide).
- Radiolabeled glibenclamide transport and metabolism studies, and assessment of its effect on organic dye transport.
Main Results:
- All three inward rectifier channels (ir, irk2, irk3) are expressed in Drosophila principal cells, suggesting roles in secretion and reabsorption.
- Inward rectifier channel inhibitors (glibenclamide, tolbutamide, minoxidil, diazoxide) completely inhibited fluid secretion.
- Glibenclamide potently inhibited fluid secretion, was transported and metabolized by the tubule, and also inhibited organic solute transport.
Conclusions:
- Inward rectifier potassium channels play a critical role in regulating fluid secretion in insect renal tubules.
- The identified channels represent a lower-affinity class, distinct from SUR-dependent channels.
- Glibenclamide exhibits complex interactions with the tubule, acting as a fluid secretion inhibitor, an organic solute transporter inhibitor, and a substrate for excretion/metabolism.