Modulation of neuronal and recombinant GABAA receptors by redox reagents

Alessandra Amato, Christopher N. Connolly, Stephen J. Moss, Trevor G. Smart

    Research output: Contribution to journalArticle

    68 Citations (Scopus)

    Abstract

    1. The functional role played by the postulated disulphide bridge in ?-aminobutyric acid type A (GABA(A)) receptors and its susceptibility to oxidation and reduction were studied using recombinant (murine receptor subunits expressed in human embryonic kidney cells) and rat neuronal GABA(A) receptors
    in conjunction with whole-cell and single channel patch-clamp
    techniques. 2. The reducing agent dithiothreitol (DTT) reversibly
    potentiated GABA-activated responses (I(GABA)) of a1ß1 or a1ß2 receptors while the oxidizing reagent 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) caused inhibition. Redox modulation of I(GABA) was independent of GABA concentration, membrane potential and the receptor agonist and did not affect the GABA EC50 or Hill coefficient. The endogenous antioxidant reduced glutathione (GSH) also potentiated I(GABA) in a1ß2 receptors, while both the oxidized form of DTT and glutathione (GSSG) caused small inhibitory effects. 3. Recombinant receptors composed of a1ß1?2S or a1ß2?2S were considerably less sensitive to DTT and DTNB. 4. For neuronal GABA(A) receptors, I(GABA) was enhanced by flurazepam and relatively unaffected by redox reagents.
    However, in cultured sympathetic neurones, nicotinic
    acetylcholine-activated responses were inhibited by DTT whilst in
    cerebellar granule neurones, NMDA-activated currents were potentiated by
    DTT and inhibited by DTNB. 5. Single GABA-activated ion channel
    currents exhibited a conductance of 16 pS for a1ß1 constructs. DTT did
    not affect the conductance or individual open time constants determined
    from dwell time histograms, but increased the mean open time by
    affecting the channel open probability without increasing the number of
    cell surface receptors. 6. A kinetic model of the effects of DTT and DTNB suggested that the receptor existed in equilibrium between oxidized and reduced forms. DTT increased the rate of entry into reduced receptor forms and also into desensitized states. DTNB reversed these kinetic effects. 7. Our results indicate that GABA(A) receptors formed by a and ß subunits are susceptible to regulation by redox agents. Inclusion of the ?2 subunit in the receptor, or recording from some neuronal GABA(A) receptors,
    resulted in reduced sensitivity to DTT and DTNB. Given the suggested
    existence of aß subunit complexes in some areas of the central nervous
    system together with the generation and release of endogenous redox compounds, native GABA(A) receptors may be subject to regulation by redox mechanisms.

    Original languageEnglish
    Pages (from-to)35-50
    Number of pages16
    JournalJournal of Physiology
    Volume517
    Issue number1
    DOIs
    Publication statusPublished - 1999

    Cite this

    Amato, Alessandra ; Connolly, Christopher N. ; Moss, Stephen J. ; Smart, Trevor G. / Modulation of neuronal and recombinant GABAA receptors by redox reagents. In: Journal of Physiology. 1999 ; Vol. 517, No. 1. pp. 35-50.
    @article{5a44e8e438e4409997f1c3de91dcd20b,
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    abstract = "1. The functional role played by the postulated disulphide bridge in ?-aminobutyric acid type A (GABA(A)) receptors and its susceptibility to oxidation and reduction were studied using recombinant (murine receptor subunits expressed in human embryonic kidney cells) and rat neuronal GABA(A) receptors in conjunction with whole-cell and single channel patch-clamp techniques. 2. The reducing agent dithiothreitol (DTT) reversibly potentiated GABA-activated responses (I(GABA)) of a1{\ss}1 or a1{\ss}2 receptors while the oxidizing reagent 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) caused inhibition. Redox modulation of I(GABA) was independent of GABA concentration, membrane potential and the receptor agonist and did not affect the GABA EC50 or Hill coefficient. The endogenous antioxidant reduced glutathione (GSH) also potentiated I(GABA) in a1{\ss}2 receptors, while both the oxidized form of DTT and glutathione (GSSG) caused small inhibitory effects. 3. Recombinant receptors composed of a1{\ss}1?2S or a1{\ss}2?2S were considerably less sensitive to DTT and DTNB. 4. For neuronal GABA(A) receptors, I(GABA) was enhanced by flurazepam and relatively unaffected by redox reagents. However, in cultured sympathetic neurones, nicotinic acetylcholine-activated responses were inhibited by DTT whilst in cerebellar granule neurones, NMDA-activated currents were potentiated by DTT and inhibited by DTNB. 5. Single GABA-activated ion channel currents exhibited a conductance of 16 pS for a1{\ss}1 constructs. DTT did not affect the conductance or individual open time constants determined from dwell time histograms, but increased the mean open time by affecting the channel open probability without increasing the number of cell surface receptors. 6. A kinetic model of the effects of DTT and DTNB suggested that the receptor existed in equilibrium between oxidized and reduced forms. DTT increased the rate of entry into reduced receptor forms and also into desensitized states. DTNB reversed these kinetic effects. 7. Our results indicate that GABA(A) receptors formed by a and {\ss} subunits are susceptible to regulation by redox agents. Inclusion of the ?2 subunit in the receptor, or recording from some neuronal GABA(A) receptors, resulted in reduced sensitivity to DTT and DTNB. Given the suggested existence of a{\ss} subunit complexes in some areas of the central nervous system together with the generation and release of endogenous redox compounds, native GABA(A) receptors may be subject to regulation by redox mechanisms.",
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    Modulation of neuronal and recombinant GABAA receptors by redox reagents. / Amato, Alessandra; Connolly, Christopher N.; Moss, Stephen J.; Smart, Trevor G.

    In: Journal of Physiology, Vol. 517, No. 1, 1999, p. 35-50.

    Research output: Contribution to journalArticle

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    T1 - Modulation of neuronal and recombinant GABAA receptors by redox reagents

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    AU - Connolly, Christopher N.

    AU - Moss, Stephen J.

    AU - Smart, Trevor G.

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    N2 - 1. The functional role played by the postulated disulphide bridge in ?-aminobutyric acid type A (GABA(A)) receptors and its susceptibility to oxidation and reduction were studied using recombinant (murine receptor subunits expressed in human embryonic kidney cells) and rat neuronal GABA(A) receptors in conjunction with whole-cell and single channel patch-clamp techniques. 2. The reducing agent dithiothreitol (DTT) reversibly potentiated GABA-activated responses (I(GABA)) of a1ß1 or a1ß2 receptors while the oxidizing reagent 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) caused inhibition. Redox modulation of I(GABA) was independent of GABA concentration, membrane potential and the receptor agonist and did not affect the GABA EC50 or Hill coefficient. The endogenous antioxidant reduced glutathione (GSH) also potentiated I(GABA) in a1ß2 receptors, while both the oxidized form of DTT and glutathione (GSSG) caused small inhibitory effects. 3. Recombinant receptors composed of a1ß1?2S or a1ß2?2S were considerably less sensitive to DTT and DTNB. 4. For neuronal GABA(A) receptors, I(GABA) was enhanced by flurazepam and relatively unaffected by redox reagents. However, in cultured sympathetic neurones, nicotinic acetylcholine-activated responses were inhibited by DTT whilst in cerebellar granule neurones, NMDA-activated currents were potentiated by DTT and inhibited by DTNB. 5. Single GABA-activated ion channel currents exhibited a conductance of 16 pS for a1ß1 constructs. DTT did not affect the conductance or individual open time constants determined from dwell time histograms, but increased the mean open time by affecting the channel open probability without increasing the number of cell surface receptors. 6. A kinetic model of the effects of DTT and DTNB suggested that the receptor existed in equilibrium between oxidized and reduced forms. DTT increased the rate of entry into reduced receptor forms and also into desensitized states. DTNB reversed these kinetic effects. 7. Our results indicate that GABA(A) receptors formed by a and ß subunits are susceptible to regulation by redox agents. Inclusion of the ?2 subunit in the receptor, or recording from some neuronal GABA(A) receptors, resulted in reduced sensitivity to DTT and DTNB. Given the suggested existence of aß subunit complexes in some areas of the central nervous system together with the generation and release of endogenous redox compounds, native GABA(A) receptors may be subject to regulation by redox mechanisms.

    AB - 1. The functional role played by the postulated disulphide bridge in ?-aminobutyric acid type A (GABA(A)) receptors and its susceptibility to oxidation and reduction were studied using recombinant (murine receptor subunits expressed in human embryonic kidney cells) and rat neuronal GABA(A) receptors in conjunction with whole-cell and single channel patch-clamp techniques. 2. The reducing agent dithiothreitol (DTT) reversibly potentiated GABA-activated responses (I(GABA)) of a1ß1 or a1ß2 receptors while the oxidizing reagent 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) caused inhibition. Redox modulation of I(GABA) was independent of GABA concentration, membrane potential and the receptor agonist and did not affect the GABA EC50 or Hill coefficient. The endogenous antioxidant reduced glutathione (GSH) also potentiated I(GABA) in a1ß2 receptors, while both the oxidized form of DTT and glutathione (GSSG) caused small inhibitory effects. 3. Recombinant receptors composed of a1ß1?2S or a1ß2?2S were considerably less sensitive to DTT and DTNB. 4. For neuronal GABA(A) receptors, I(GABA) was enhanced by flurazepam and relatively unaffected by redox reagents. However, in cultured sympathetic neurones, nicotinic acetylcholine-activated responses were inhibited by DTT whilst in cerebellar granule neurones, NMDA-activated currents were potentiated by DTT and inhibited by DTNB. 5. Single GABA-activated ion channel currents exhibited a conductance of 16 pS for a1ß1 constructs. DTT did not affect the conductance or individual open time constants determined from dwell time histograms, but increased the mean open time by affecting the channel open probability without increasing the number of cell surface receptors. 6. A kinetic model of the effects of DTT and DTNB suggested that the receptor existed in equilibrium between oxidized and reduced forms. DTT increased the rate of entry into reduced receptor forms and also into desensitized states. DTNB reversed these kinetic effects. 7. Our results indicate that GABA(A) receptors formed by a and ß subunits are susceptible to regulation by redox agents. Inclusion of the ?2 subunit in the receptor, or recording from some neuronal GABA(A) receptors, resulted in reduced sensitivity to DTT and DTNB. Given the suggested existence of aß subunit complexes in some areas of the central nervous system together with the generation and release of endogenous redox compounds, native GABA(A) receptors may be subject to regulation by redox mechanisms.

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