title: Isovaline does not activate GABA(B) receptor-coupled potassium currents in GABA(B) expressing AtT-20 cells and cultured rat hippocampal neurons.
abstract: Isovaline is a non-proteinogenic amino acid that has analgesic properties. R-isovaline is a proposed agonist of the γ-aminobutyric acid type B (GABA(B)) receptor in the thalamus and peripheral tissue. Interestingly, the responses to R-isovaline differ from those of the canonical GABA(B) receptor agonist R-baclofen, warranting further investigation. Using whole cell recording techniques we explored isovaline actions on GABA(B) receptors coupled to rectifying K+ channels in cells of recombinant and native receptor preparations. In AtT-20 cells transfected with GABA(B) receptor subunits, bath application of the GABA(B) receptor agonists, GABA (1 μM) and R-baclofen (5 μM) produced inwardly rectifying currents that reversed approximately at the calculated reversal potential for K+ R- isovaline (50 μM to 1 mM) and S-isovaline (500 μM) did not evoke a current. R-isovaline applied either extracellularly (250 μM) or intracellularly (10 μM) did not alter responses to GABA at 1 μM. Co-administration of R-isovaline (250 μM) with a low concentration (10 nM) of GABA did not result in a response. In cultured rat hippocampal neurons that natively express GABA(B) receptors, R-baclofen (5 μM) induced GABA(B) receptor-dependent inward currents. Under the same conditions R-isovaline (1 or 50 μM) did not evoke a current or significantly alter R-baclofen-induced effects. Therefore, R-isovaline does not interact with recombinant or native GABA(B) receptors to open K+ channels in these preparations.
authors.affiliation: Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Kimberley A
authors.initials: KA
authors.lastname: Pitman
authors.affiliation: Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Borgland
authors.affiliation: Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Bernard
authors.initials: B
authors.lastname: MacLeod
authors.affiliation: Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Ernest
authors.initials: E
authors.lastname: Puil
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D005260:Female; D058786:GABA-B Receptor Agonists / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000196:embryology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018613:Microscopy, Confocal; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D018080:Receptors, GABA-B / Q000235:genetics / Q000378:metabolism*; D014633:Valine / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D058786:GABA-B Receptor Agonists; D024661:Potassium Channels, Inwardly Rectifying; D018080:Receptors, GABA-B; D049452:Green Fluorescent Proteins; D005680:gamma-Aminobutyric Acid; C032737:isovaline; D001418:Baclofen; D014633:Valine