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Published on: August 16, 2018
R-Isovaline: a subtype-specific agonist at GABA(B)-receptors?
J E Cooke1, D A Mathers, E Puil
1Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
R-isovaline, an analgesic amino acid, activates metabotropic GABA(B) receptors in thalamic neurons by increasing potassium (K+) conductance. This activation is G protein-mediated and distinct from baclofen
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- R-isovaline, an analgesic amino acid, shares structural similarities with glycine and GABA.
- Previous studies indicated R-isovaline's actions on thalamic neurons involve K+ conductance independent of chloride gradients.
Purpose of the Study:
- To investigate whether R-isovaline activates metabotropic GABA(B) receptors.
- To characterize the mechanism of R-isovaline's action on thalamic neurons.
Main Methods:
- Whole-cell voltage-clamp recordings in rat thalamic neuron slices.
- Immunocytochemistry to visualize GABA(B1) and GABA(B2) receptor subunits.
- Application of R-isovaline via bath perfusion and local ejection, alongside GABA(B) agonists/antagonists and modulators.
Main Results:
- R-isovaline application increased membrane conductance and outward rectification in 70% of neurons, reversing near the K+ Nernst potential.
- Effects were G protein-mediated, blocked by GABA(B) antagonists (CGP35348, CGP52432), and enhanced by a GABA(B) allosteric modulator (CGP7930).
- R-isovaline-induced currents were long-lasting and distinct from baclofen responses, suggesting different binding sites or conformational changes.
Conclusions:
- R-isovaline increases K+ channel conductance through metabotropic GABA(B) receptors.
- R-isovaline's mechanism of action differs from baclofen, despite shared receptor activation.
- The distinct kinetic and pharmacological profiles suggest unique interactions with the GABA(B) receptor complex.
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