Pharmacological characterization of a novel cell line expressing human alpha(4)beta(3)delta GABA(A) receptors.
Journal: 2003/March - British Journal of Pharmacology
ISSN: 0007-1188
Abstract:
1: The pharmacology of the stable cell line expressing human alpha(4)beta(3)delta GABA(A) receptor was investigated using whole-cell patch-clamp techniques. 2: alpha(4)beta(3)delta receptors exhibited increased sensitivity to GABA when compared to alpha(4)beta(3)gamma(2) receptors, with EC(50)'s of 0.50 (0.46, 0.53) microM and 2.6 (2.5, 2.6) microM respectively. Additionally, the GABA partial agonists piperidine-4-sulphonate (P4S) and 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridin-3-ol (THIP) displayed markedly higher efficacy at alpha(4)beta(3)delta receptors, indeed THIP demonstrated greater efficacy than GABA at these receptors. 3: The delta subunit conferred slow desensitization to GABA, with rate constants of 4.8+/-0.5 s for alpha(4)beta(3)delta and 2.5+/-0.2 s for alpha(4)beta(3)gamma(2). However, both P4S and THIP demonstrated similar levels of desensitization on both receptor subtypes suggesting this effect is agonist specific. 4: alpha(4)beta(3)delta and alpha(4)beta(3)gamma(2) demonstrated equal sensitivity to inhibition by the cation zinc (2-3 microM IC(50)). However, alpha(4)beta(3)delta receptors demonstrated greater sensitivity to inhibition by lanthanum. The IC(50) for GABA antagonists SR-95531 and picrotoxin, was similar for alpha(4)beta(3)delta and alpha(4)beta(3)gamma(2). Likewise, inhibition was observed on both subtypes at high and low pH. 5: alpha(4)beta(3)delta receptors were insensitive to modulation by benzodiazepine ligands. In contrast Ro15-4513 and bretazenil potentiated GABA responses on alpha(4)beta(3)gamma(2) cells, and the inverse agonist DMCM showed allosteric inhibition of alpha(4)beta(3)gamma(2) receptors. 6: The efficacy of neurosteroids at alpha(4)beta(3)delta receptors was greatly enhanced over that observed at alpha(4)beta(3)gamma(2) receptors. The greatest effect was observed using THDOC with 524+/-71.6% potentiation at alpha(4)beta(3)delta and 297.9+/-49.7% at alpha(4)beta(3)gamma(2) receptors. Inhibition by the steroid pregnenolone sulphate however, showed no subtype selectivity. The efficacy of both pentobarbitone and propofol was slightly augmented and etomidate greatly enhanced at alpha(4)beta(3)delta receptors versus alpha(4)beta(3)gamma(2) receptors. 7: We show that the alpha(4)beta(3)delta receptor has a distinct pharmacology and kinetic profile. With its restricted distribution within the brain and unique pharmacology this receptor may play an important role in the action of neurosteroids and anaesthetics. British Journal of Pharmacology (2002) 136, 965-974
Relations:
Content
Citations
(215)
References
(38)
Drugs
(1)
Chemicals
(7)
Organisms
(3)
Processes
(4)
Anatomy
(2)
Similar articles
Articles by the same authors
Discussion board
Br J Pharmacol 136(7): 965-974

Pharmacological characterization of a novel cell line expressing human <em>α</em><sub>4</sub><em>β</em><sub>3</sub><em>δ</em> GABA<sub>A</sub> receptors

1Merck Sharp &amp; Dohme Research Laboratories, Neuroscience Research Centre, Terlings Park, Eastwick Road, Harlow, Essex CM20 2QR
Author for correspondence: moc.kcrem@droffaw_htiek
Received 2002 Jan 3; Revised 2002 Mar 13; Accepted 2002 Mar 27.

Abstract

  1. The pharmacology of the stable cell line expressing human α4β3δ GABAA receptor was investigated using whole-cell patch-clamp techniques.

  2. α4β3δ receptors exhibited increased sensitivity to GABA when compared to α4β3γ2 receptors, with EC50's of 0.50 (0.46, 0.53) μM and 2.6 (2.5, 2.6) μM respectively. Additionally, the GABA partial agonists piperidine-4-sulphonate (P4S) and 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridin-3-ol (THIP) displayed markedly higher efficacy at α4β3δ receptors, indeed THIP demonstrated greater efficacy than GABA at these receptors.

  3. The δ subunit conferred slow desensitization to GABA, with rate constants of 4.8±0.5 s for α4β3δ and 2.5±0.2 s for α4β3γ2. However, both P4S and THIP demonstrated similar levels of desensitization on both receptor subtypes suggesting this effect is agonist specific.

  4. α4β3δ and α4β3γ2 demonstrated equal sensitivity to inhibition by the cation zinc (2–3 μM IC50). However, α4β3δ receptors demonstrated greater sensitivity to inhibition by lanthanum. The IC50 for GABA antagonists SR-95531 and picrotoxin, was similar for α4β3δ and α4β3γ2. Likewise, inhibition was observed on both subtypes at high and low pH.

  5. α4β3δ receptors were insensitive to modulation by benzodiazepine ligands. In contrast Ro15-4513 and bretazenil potentiated GABA responses on α4β3γ2 cells, and the inverse agonist DMCM showed allosteric inhibition of α4β3γ2 receptors.

  6. The efficacy of neurosteroids at α4β3δ receptors was greatly enhanced over that observed at α4β3γ2 receptors. The greatest effect was observed using THDOC with 524±71.6% potentiation at α4β3δ and 297.9±49.7% at α4β3γ2 receptors. Inhibition by the steroid pregnenolone sulphate however, showed no subtype selectivity. The efficacy of both pentobarbitone and propofol was slightly augmented and etomidate greatly enhanced at α4β3δ receptors versus α4β3γ2 receptors.

  7. We show that the α4β3δ receptor has a distinct pharmacology and kinetic profile. With its restricted distribution within the brain and unique pharmacology this receptor may play an important role in the action of neurosteroids and anaesthetics.

Keywords: Delta subunit, GABAA receptor, anaesthetic, neurosteroid, alpha 4 subunit, benzodiazepine, desensitization, inhibitory neurotransmission, allosteric modulation
Abstract

Abbreviations

Alphaxalone5α-pregnan-3α-ol-11,20-di-one
DMCMMethyl-6,7,-dimethoxy-4-ethyl-beta-carboline-3-carboxylate
GABAγ-aminobutyric acid
HEPES4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid
P4Spiperidine-4-sulphonic acid
Pregnenolone sulphate5α-pregnen-3β-ol-20-one sulfate
THDOC5α-pregnane-3α,21-diol-20-one
THIPtetrahydroisothiazolo-[5,4-c]pyridin-3-ol
Abbreviations
Collaboration tool especially designed for Life Science professionals.Drag-and-drop any entity to your messages.