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Pharmacological characterisation of murine α4β1δ GABAA receptors expressed in Xenopus oocytes.

Villumsen IS, Wellendorph P, Smart TG - BMC Neurosci (2015)

Bottom Line: GABAA receptor subunit composition has a profound effect on the receptor's physiological and pharmacological properties.The neurosteroid tetrahydro-deoxycorticosterone (THDOC) significantly increased GABA-initiated responses in concentrations above 30 nM for α4β1δ receptors.This study highlights some notable differences in the pharmacology of murine and human α4β1δ receptors.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK. inge_villumsen@hotmail.com.

ABSTRACT

Background: GABAA receptor subunit composition has a profound effect on the receptor's physiological and pharmacological properties. The receptor β subunit is widely recognised for its importance in receptor assembly, trafficking and post-translational modifications, but its influence on extrasynaptic GABAA receptor function is less well understood. Here, we examine the pharmacological properties of a potentially native extrasynaptic GABAA receptor that incorporates the β1 subunit, specifically composed of α4β1δ and α4β1 subunits.

Results: GABA activated concentration-dependent responses at α4β1δ and α4β1 receptors with EC50 values in the nanomolar to micromolar range, respectively. The divalent cations Zn(2+) and Cu(2+), and the β1-selective inhibitor salicylidine salicylhydrazide (SCS), inhibited GABA-activated currents at α4β1δ receptors. Surprisingly the α4β1 receptor demonstrated biphasic sensitivity to Zn(2+) inhibition that may reflect variable subunit stoichiometries with differing sensitivity to Zn(2+). The neurosteroid tetrahydro-deoxycorticosterone (THDOC) significantly increased GABA-initiated responses in concentrations above 30 nM for α4β1δ receptors.

Conclusions: With this study we report the first pharmacological characterisation of various GABAA receptor ligands acting at murine α4β1δ GABAA receptors, thereby improving our understanding of the molecular pharmacology of this receptor isoform. This study highlights some notable differences in the pharmacology of murine and human α4β1δ receptors. We consider the likelihood that the α4β1δ receptor may play a role as an extrasynaptic GABAA receptor in the nervous system.

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Examples of GABA-activated currents recorded from cDNA-injectedXenopusoocytes expressing α4β1δ and α4β1 receptors. A, Representative membrane currents for α4β1δ receptors (upper panel) and α4β1 receptors (lower panel) in response to increasing concentrations of GABA. The oocytes were voltage clamped at -60 mV. B, GABA concentration response curves for α4β1δ (n = 6) and α4β1(n = 5) receptors. All data points represent means ± SEMs.
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Fig1: Examples of GABA-activated currents recorded from cDNA-injectedXenopusoocytes expressing α4β1δ and α4β1 receptors. A, Representative membrane currents for α4β1δ receptors (upper panel) and α4β1 receptors (lower panel) in response to increasing concentrations of GABA. The oocytes were voltage clamped at -60 mV. B, GABA concentration response curves for α4β1δ (n = 6) and α4β1(n = 5) receptors. All data points represent means ± SEMs.

Mentions: GABA concentration response curves were generated for α4β1 and α4β1δ receptors to evaluate GABA potency at these receptors. Oocytes were challenged with increasing concentrations of GABA (Figure 1A). Depending upon expression levels, maximal currents to GABA ranged from 100 to 3000 nA for cells expressing α4β1 receptors and from 300 to 3000 nA for cells expressing α4β1δ receptors. The holding currents were between 0 and -40 nA and the receptors were not constitutively active. The GABA EC50 values were 0.89 μM for α4β1δ receptors and 2.7 μM for α4β1 receptors (Figure 1B, Table 1). GABA concentration-response data were fitted as monophasic curves, with Hill coefficients of 1.1 and 0.87 for α4β1δ and α4β1 receptors, respectively (Table 1).Figure 1


Pharmacological characterisation of murine α4β1δ GABAA receptors expressed in Xenopus oocytes.

Villumsen IS, Wellendorph P, Smart TG - BMC Neurosci (2015)

Examples of GABA-activated currents recorded from cDNA-injectedXenopusoocytes expressing α4β1δ and α4β1 receptors. A, Representative membrane currents for α4β1δ receptors (upper panel) and α4β1 receptors (lower panel) in response to increasing concentrations of GABA. The oocytes were voltage clamped at -60 mV. B, GABA concentration response curves for α4β1δ (n = 6) and α4β1(n = 5) receptors. All data points represent means ± SEMs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4359537&req=5

Fig1: Examples of GABA-activated currents recorded from cDNA-injectedXenopusoocytes expressing α4β1δ and α4β1 receptors. A, Representative membrane currents for α4β1δ receptors (upper panel) and α4β1 receptors (lower panel) in response to increasing concentrations of GABA. The oocytes were voltage clamped at -60 mV. B, GABA concentration response curves for α4β1δ (n = 6) and α4β1(n = 5) receptors. All data points represent means ± SEMs.
Mentions: GABA concentration response curves were generated for α4β1 and α4β1δ receptors to evaluate GABA potency at these receptors. Oocytes were challenged with increasing concentrations of GABA (Figure 1A). Depending upon expression levels, maximal currents to GABA ranged from 100 to 3000 nA for cells expressing α4β1 receptors and from 300 to 3000 nA for cells expressing α4β1δ receptors. The holding currents were between 0 and -40 nA and the receptors were not constitutively active. The GABA EC50 values were 0.89 μM for α4β1δ receptors and 2.7 μM for α4β1 receptors (Figure 1B, Table 1). GABA concentration-response data were fitted as monophasic curves, with Hill coefficients of 1.1 and 0.87 for α4β1δ and α4β1 receptors, respectively (Table 1).Figure 1

Bottom Line: GABAA receptor subunit composition has a profound effect on the receptor's physiological and pharmacological properties.The neurosteroid tetrahydro-deoxycorticosterone (THDOC) significantly increased GABA-initiated responses in concentrations above 30 nM for α4β1δ receptors.This study highlights some notable differences in the pharmacology of murine and human α4β1δ receptors.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Physiology & Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK. inge_villumsen@hotmail.com.

ABSTRACT

Background: GABAA receptor subunit composition has a profound effect on the receptor's physiological and pharmacological properties. The receptor β subunit is widely recognised for its importance in receptor assembly, trafficking and post-translational modifications, but its influence on extrasynaptic GABAA receptor function is less well understood. Here, we examine the pharmacological properties of a potentially native extrasynaptic GABAA receptor that incorporates the β1 subunit, specifically composed of α4β1δ and α4β1 subunits.

Results: GABA activated concentration-dependent responses at α4β1δ and α4β1 receptors with EC50 values in the nanomolar to micromolar range, respectively. The divalent cations Zn(2+) and Cu(2+), and the β1-selective inhibitor salicylidine salicylhydrazide (SCS), inhibited GABA-activated currents at α4β1δ receptors. Surprisingly the α4β1 receptor demonstrated biphasic sensitivity to Zn(2+) inhibition that may reflect variable subunit stoichiometries with differing sensitivity to Zn(2+). The neurosteroid tetrahydro-deoxycorticosterone (THDOC) significantly increased GABA-initiated responses in concentrations above 30 nM for α4β1δ receptors.

Conclusions: With this study we report the first pharmacological characterisation of various GABAA receptor ligands acting at murine α4β1δ GABAA receptors, thereby improving our understanding of the molecular pharmacology of this receptor isoform. This study highlights some notable differences in the pharmacology of murine and human α4β1δ receptors. We consider the likelihood that the α4β1δ receptor may play a role as an extrasynaptic GABAA receptor in the nervous system.

Show MeSH