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Title: Investigation of an unusual GABA-A receptor : studies on the promiscuous ε subunit
Author: Schwabe, T.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2010
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γ-aminobutyric acid (GABA) type A (GABAA) receptors are pentameric, chloride-selective ion channels. Nineteen different GABAA receptor subunits are known to exist in man and various subunit combinations are able to form receptor subtypes with different, subunit-specific pharmacological properties. GABAA receptors are targeted by many clinically-important drugs, for example, benzodiazepines. Unwanted side effects, such as tolerance and dependence, often occur due to non-selective receptor targeting. There is, therefore, a need for subtype-selective drugs. Comparatively little is known about the role of the ε subunit or ε-subunit-containing receptors in vivo. Recently, it has been recognised that a GABAA receptor subtype, that contains the α3 and ε subunits, is present in neurons within the forebrain that synthesise acetylcholine, and this may regulate neurotransmitter release. In Alzheimer’s disease, cholinergic neurotransmission is reduced; therefore, this subtype might be a target for the development of anti-Alzheimer’s disease drugs that would function by increasing acetylcholine release in forebrain regions where cholinergic neurons are dying. The pharmacological properties of a GABAA receptor that comprises the α3, β2 and ε subunits were examined in Xenopus laevis oocytes using the two-electrode voltage-clamp technique. The results obtained confirm that the ε subunit confers unusual properties on the GABAA receptor. The results obtained confirm that the ε subunit confers unusual properties on the GABAA receptor. α3β2ε receptors were spontaneously active and displayed high agonist sensitivity. Next, a screening assay was established in human embryonic kidney 293 cells, which were transiently transfected with complementary DNAs for GABAA receptor subunits and a yellow fluorescence protein variant (YFP-H148Q/I152L). The latter is quenched by anion influx into cells upon receptor activation. Using this assay, receptor activity and GABA-concentration relationships could be demonstrated. It was, therefore, used to screen for compounds that modulate the activity of ε-subunit-containing receptors. Several interesting compounds were identified, and they were further examined using the two-electrode voltage-clamp technique. These compounds are potential candidates for drug development, and may help to identify the physiological role(s) of GABAA receptors that contain the ε polypeptide in vivo.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available