Mozibur Rahman

Pregnenolone sulphate and Zn2+ inhibit recombinant rat GABAA receptor through different channel property

Aims:  We compared the antagonistic effects of state‐dependent gamma‐aminobutyric acid A (GABAA) receptor blockers picrotoxin, Zn2+ and pregnenolone sulphate (PS) on GABA‐ and pentobarbital‐activated currents in recombinant rat GABAA receptors in Xenopus oocytes.

GABA-site antagonism and pentobarbital actions do not depend on the α-subunit type in the recombinant rat GABAA receptor

Aim:  The roles of α‐subunits on the gamma‐aminobutyric acid (GABA)‐site antagonism and pentobarbital actions were examined in rat recombinant GABAA receptors in Xenopus oocytes.

A COMPARISON OF THE PHARMACOLOGICAL PROPERTIES OF RECOMBINANT HUMAN AND RAT α1β2γ2L GABAA RECEPTORS IN XENOPUS OOCYTES

1 In the present study, we compared the pharmacology, particularly neurosteroid modulation of the GABAA receptor, between human and rat a1b2g2L GABAA receptors and between human receptors containing the long (L) and short (S) forms of the g2‐subunit. 2 We observed that maximum responses to GABA were significantly higher with the human a1b2g2L receptor compared with the rat receptor. In terms of neurosteroid modulation, increases in the EC15 response to GABA induced by 3a‐OH‐5b‐pregnan‐20‐one (3a5bP), 5a‐androstane‐3a,17b‐diol (3a5aADL) and 5a‐pregnane‐3a,20b‐diol (3a5a‐diol) were significantly greater for the rat compared with the human receptor. Responses to 30 mmol/L GABA were inhibited by 3b‐OH‐5a‐pregnan‐20‐one (UC1010) and 5b‐pregnan‐3b,20(R)‐diol (UC1020) to a greater degree for human and rat receptors, respectively. Responses to GABA + 3a5aTHDOC were inhibited by 5a‐pregnan‐3b,20(S)‐diol (UC1019) and pregnenolone sulphate to a greater degree for human and rat receptors, respectively. 3 The GABA dose–response curves for human a1b2g2S and a1b2g2L receptors were identical. However, the maximum GABA‐evoked current, the direct gating effect of pentobarbital and the allosteric potentiation of the GABA EC15 response by 3a5aTHDOC and 3a5bP were significantly higher with a1b2g2S than a1b2g2L receptors. Inhibition of the response to 30 mmol/L GABA by UC1010 and UC1020 was greater for a1b2g2L and a1b2g2S receptors, respectively. Inhibition of responses to 3a5aTHDOC + GABA by UC1019 and UC1010 was significantly higher for a1b2g2L receptors. 4 In conclusion, the site of activation by GABA and neurosteroid modulation differ between human and rat a1b2g2L receptors, as well as between human receptors containing the L and S splice variants of the g2‐subunit.

Agonist function of the recombinant α4β3δ GABAA receptor is dependent on the human and rat variants of the α4‐subunit

1. It is known that the α4‐subunit is likely to occur in the brain predominantly in α4β3δ receptors at extrasynaptic sites. Recent studies have revealed that the α1‐, α4‐, γ2‐ and δ‐subunits may colocalize extrasynaptically in dentate granule cells of the hippocampus. In the present study, we characterized a series of recombinant GABAA receptors containing human (H) and rat (R) α1/α4‐, β2/β3‐ and γ2S/δ‐subunits in Xenopus oocytes using the two‐electrode voltage‐clamp technique.

Agonist function of the recombinant alpha 4 beta 3 delta GABAA receptor is dependent on the human and rat variants of the alpha 4-subunit.

1. It is known that the α4‐subunit is likely to occur in the brain predominantly in α4β3δ receptors at extrasynaptic sites. Recent studies have revealed that the α1‐, α4‐, γ2‐ and δ‐subunits may colocalize extrasynaptically in dentate granule cells of the hippocampus. In the present study, we characterized a series of recombinant GABAA receptors containing human (H) and rat (R) α1/α4‐, β2/β3‐ and γ2S/δ‐subunits in Xenopus oocytes using the two‐electrode voltage‐clamp technique.

Agonist function of the recombinant α4β3δ GABAA receptor is dependent on the human and rat variants of the α4-subunit: Agonist function at α4ß3δ GABAA receptors

1. It is known that the α4‐subunit is likely to occur in the brain predominantly in α4β3δ receptors at extrasynaptic sites. Recent studies have revealed that the α1‐, α4‐, γ2‐ and δ‐subunits may colocalize extrasynaptically in dentate granule cells of the hippocampus. In the present study, we characterized a series of recombinant GABAA receptors containing human (H) and rat (R) α1/α4‐, β2/β3‐ and γ2S/δ‐subunits in Xenopus oocytes using the two‐electrode voltage‐clamp technique.

Neurosteroid: Molecular Mechanisms of Action on the GABAA Receptor

Neurosteroids represent a class of endogenous steroids that are synthesized in the brain, the adrenals and the gonads and have potent and selective effects on the gamma-aminobutyric acid type A (GABA A receptor). 3α-Hydroxy A-ring-reduced metabolites of progesterone, deoxycorticosterone and testosterone enhance the the Cl flux through GABA A receptor conductance at nanomolar concentrations in a non-genomic (rapid and direct) manner. Studies on the GABA A receptors have shown that allopregnanolone (3α-OH-5α-pregnan-20-one), 5α-androstane-3α,17αdiol (Adiol) and (3 5 3, 21-dihydroxypregnan-20-one (3α5αTHDOC) enhance the GABA mediated Cl currents acting on a site (or sites) distinct from the GABA, benzodiazepine, barbiturate and picrotoxin binding sites. This modulation site (or sites) has a well-defined structure–activity relationship with a 3α-hydroxy and a 20-ketone configuration in the pregnane molecule required for agonist action. However, the neurosteroid pregnenolone sulfate (PS) is a non-competitive GABA A receptor antagonist and inhibits GABA-activated Cl currents in an activationdependent manner. 3β-hydroxy A-ring reduced pregnane steroids are pregnenolone sulfate-like GABA A receptors antagonists and inhibit the GABA A receptor’s function and its potentiation induced by their 3α-diasteromers in a non-competitive manner. The specificity of neurosteroid action on the GABA A receptor results from a variety of molecular mechanisms, including receptor subunit composition, receptor activation–deactivation, and steroid concentration. Here, we will review the GABAmodulatory actions of the neurosteroids. The molecular mechanisms underpinning the non-genomic effect of agonist and antagonist neurosteroids will be discussed with particular emphasis being given to the role of GABA A receptor isoforms.