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Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Direct membrane effects of morphine and endorphins on Amoeba proteus
1Département de Sciences Biologiques, Université de Montréal, Canada.
Abstract:
Morphine, leu-enkephalinamide, met-enkephalin, alpha-neoendorphin and its Arg8 1-8 fragment increase contractile vacuole output in the freshwater Amoeba proteus at 18 microM. Significant effects of leu-enkephalin and naloxone are obtained at 180 microM. All compounds have reached their maximal activity at 720 microM. Alpha-neoendorphin and leu-enkephalin are inactive in the presence of isotonic, non-penetration sucrose, hence these compounds increase plasma membrane permeability to water. Results from molecular modeling show a clear correlation of activity with amphiphilicity, charge distribution and general flexibility of molecules. We conclude that, like previously-studied vasopressin analogues and non-hormonal amphiphilic peptides, active opioids embed themselves into the Amoeba plasma membrane, disrupting the lipid bilayer and increasing its permeability. In our Amoeba system, naloxone, a general morphine-like inhibitor, blocks active opioids as well as a vasopressin analogue. Naloxone, being less active than other tested amphiphiles, acts as a membrane stabilizer, protecting the lipid bilayer against the disruption action of more active compounds.
Insights
Opioid peptides like morphine increase water expulsion in Amoeba proteus by altering cell membrane permeability. Naloxone, an opioid inhibitor, stabilizes the membrane, preventing this effect.
Area of Science:
- Cell Biology
- Biochemistry
- Pharmacology
Background:
- Opioid peptides, known for their roles in mammalian systems, are being investigated for broader biological functions.
- The freshwater Amoeba proteus serves as a model organism to study cellular processes like membrane transport.
Purpose of the Study:
- To investigate the effects of various opioid peptides on contractile vacuole function in Amoeba proteus.
- To determine the mechanism by which opioids influence membrane permeability and water transport.
- To explore the role of naloxone as a potential modulator of opioid effects on cell membranes.
Main Methods:
- Exposure of Amoeba proteus to different concentrations of opioid peptides (morphine, leu-enkephalinamide, met-enkephalin, alpha-neoendorphin, leu-enkephalin) and naloxone.
- Measurement of contractile vacuole output as an indicator of water transport.
- Experiments using isotonic, non-penetrating sucrose solutions to assess membrane permeability.
- Molecular modeling to correlate molecular properties with observed biological activity.
Main Results:
- Opioid peptides significantly increased contractile vacuole output in Amoeba proteus, indicating enhanced water expulsion.
- Alpha-neoendorphin and leu-enkephalin demonstrated increased plasma membrane permeability to water.
- Molecular modeling revealed a correlation between molecular amphiphilicity, charge distribution, flexibility, and biological activity.
- Naloxone inhibited the effects of active opioids and a vasopressin analogue, suggesting a membrane-stabilizing role.
Conclusions:
- Active opioids interact with the Amoeba plasma membrane, embedding into the lipid bilayer and increasing its permeability, similar to vasopressin analogues and amphiphilic peptides.
- Naloxone acts as a membrane stabilizer, counteracting the disruptive effects of amphiphilic compounds on the lipid bilayer.
- The Amoeba system provides a valuable model for understanding the membrane-level interactions of opioid peptides and their inhibitors.
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