Kinetics and spontaneous open probability conferred by the epsilon subunit of the GABAA receptor

David A. Wagner, Marcel P. Goldschen-Ohm, Tim G. Hales, Mathew V. Jones

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

GABAA receptors mediate synaptic and extrasynaptic inhibition. Native receptors consist of alpha and beta subunits, which are required for function, and another "modulatory" subunit, for example, gamma, delta, or epsilon. Of these, the epsilon subunit has the most restricted distribution, confers resistance to neurosteroid and anesthetic modulation, and causes spontaneous channel opening. Little is known, however, about how epsilon affects receptor kinetics, which in turn shape responses to both ambient and synaptic GABA exposure. Here, we expressed human alpha2beta1, alpha2beta1gamma2, or alpha2beta1epsilon subunit combinations in human embryonic kidney 293 cells and used rapid solution exchange to study receptor kinetics in outside-out patches. The epsilon subunit greatly slowed deactivation and recovery after brief GABA pulses. During long, saturating GABA pulses, the rate of desensitization was slower for alpha2beta1epsilon and alpha2beta1gamma2 than for alpha2beta1. However, in alpha2beta1epsilon, the final extent of desensitization was large compared with that of alpha2beta1gamma2. Responses in alpha2beta1epsilon, but not the others, were often followed by an "overshoot" above the baseline, suggesting that a fraction of channels are spontaneously open and are transiently silenced by receptor activation and subsequent desensitization. The baseline current and associated noise were reduced by picrotoxin, revealing that epsilon-containing channels are open approximately 4% of the time in the absence of GABA. These results suggest that, if epsilon-containing receptors are expressed at synapses, the synaptic currents would be long-lasting but may rundown quickly under high-frequency activation. In addition, silencing of spontaneous openings by desensitization raises the possibility that tonic inhibition mediated by epsilon-containing receptors may be regulated by phasic inhibition.

Original languageEnglish
Pages (from-to)10462-10468
Number of pages7
JournalJournal of Neuroscience
Volume25
Issue number45
DOIs
Publication statusPublished - 9 Nov 2005

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GABA-A Receptors
gamma-Aminobutyric Acid
Picrotoxin
Synapses
Neurotransmitter Agents
Anesthetics
Noise
Heart Rate
Kidney
epsilon receptor

Keywords

  • Cell Line
  • Dose-Response Relationship, Drug
  • Dose-Response Relationship, Radiation
  • Electric Stimulation/methods
  • GABA Antagonists/pharmacology
  • Humans
  • Ion Channel Gating/drug effects
  • Kinetics
  • Membrane Potentials/drug effects
  • Neural Inhibition/drug effects
  • Patch-Clamp Techniques/methods
  • Picrotoxin/pharmacology
  • Probability
  • Protein Subunits/physiology
  • Receptors, GABA-A/genetics
  • Synaptic Transmission/drug effects
  • Time Factors
  • Transfection/methods
  • gamma-Aminobutyric Acid/pharmacology

Cite this

@article{0f3fa14251464bb69674a9031ae65898,
title = "Kinetics and spontaneous open probability conferred by the epsilon subunit of the GABAA receptor",
abstract = "GABAA receptors mediate synaptic and extrasynaptic inhibition. Native receptors consist of alpha and beta subunits, which are required for function, and another {"}modulatory{"} subunit, for example, gamma, delta, or epsilon. Of these, the epsilon subunit has the most restricted distribution, confers resistance to neurosteroid and anesthetic modulation, and causes spontaneous channel opening. Little is known, however, about how epsilon affects receptor kinetics, which in turn shape responses to both ambient and synaptic GABA exposure. Here, we expressed human alpha2beta1, alpha2beta1gamma2, or alpha2beta1epsilon subunit combinations in human embryonic kidney 293 cells and used rapid solution exchange to study receptor kinetics in outside-out patches. The epsilon subunit greatly slowed deactivation and recovery after brief GABA pulses. During long, saturating GABA pulses, the rate of desensitization was slower for alpha2beta1epsilon and alpha2beta1gamma2 than for alpha2beta1. However, in alpha2beta1epsilon, the final extent of desensitization was large compared with that of alpha2beta1gamma2. Responses in alpha2beta1epsilon, but not the others, were often followed by an {"}overshoot{"} above the baseline, suggesting that a fraction of channels are spontaneously open and are transiently silenced by receptor activation and subsequent desensitization. The baseline current and associated noise were reduced by picrotoxin, revealing that epsilon-containing channels are open approximately 4{\%} of the time in the absence of GABA. These results suggest that, if epsilon-containing receptors are expressed at synapses, the synaptic currents would be long-lasting but may rundown quickly under high-frequency activation. In addition, silencing of spontaneous openings by desensitization raises the possibility that tonic inhibition mediated by epsilon-containing receptors may be regulated by phasic inhibition.",
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author = "Wagner, {David A.} and Goldschen-Ohm, {Marcel P.} and Hales, {Tim G.} and Jones, {Mathew V.}",
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language = "English",
volume = "25",
pages = "10462--10468",
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Kinetics and spontaneous open probability conferred by the epsilon subunit of the GABAA receptor. / Wagner, David A.; Goldschen-Ohm, Marcel P.; Hales, Tim G.; Jones, Mathew V.

In: Journal of Neuroscience, Vol. 25, No. 45, 09.11.2005, p. 10462-10468.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Kinetics and spontaneous open probability conferred by the epsilon subunit of the GABAA receptor

AU - Wagner, David A.

AU - Goldschen-Ohm, Marcel P.

AU - Hales, Tim G.

AU - Jones, Mathew V.

PY - 2005/11/9

Y1 - 2005/11/9

N2 - GABAA receptors mediate synaptic and extrasynaptic inhibition. Native receptors consist of alpha and beta subunits, which are required for function, and another "modulatory" subunit, for example, gamma, delta, or epsilon. Of these, the epsilon subunit has the most restricted distribution, confers resistance to neurosteroid and anesthetic modulation, and causes spontaneous channel opening. Little is known, however, about how epsilon affects receptor kinetics, which in turn shape responses to both ambient and synaptic GABA exposure. Here, we expressed human alpha2beta1, alpha2beta1gamma2, or alpha2beta1epsilon subunit combinations in human embryonic kidney 293 cells and used rapid solution exchange to study receptor kinetics in outside-out patches. The epsilon subunit greatly slowed deactivation and recovery after brief GABA pulses. During long, saturating GABA pulses, the rate of desensitization was slower for alpha2beta1epsilon and alpha2beta1gamma2 than for alpha2beta1. However, in alpha2beta1epsilon, the final extent of desensitization was large compared with that of alpha2beta1gamma2. Responses in alpha2beta1epsilon, but not the others, were often followed by an "overshoot" above the baseline, suggesting that a fraction of channels are spontaneously open and are transiently silenced by receptor activation and subsequent desensitization. The baseline current and associated noise were reduced by picrotoxin, revealing that epsilon-containing channels are open approximately 4% of the time in the absence of GABA. These results suggest that, if epsilon-containing receptors are expressed at synapses, the synaptic currents would be long-lasting but may rundown quickly under high-frequency activation. In addition, silencing of spontaneous openings by desensitization raises the possibility that tonic inhibition mediated by epsilon-containing receptors may be regulated by phasic inhibition.

AB - GABAA receptors mediate synaptic and extrasynaptic inhibition. Native receptors consist of alpha and beta subunits, which are required for function, and another "modulatory" subunit, for example, gamma, delta, or epsilon. Of these, the epsilon subunit has the most restricted distribution, confers resistance to neurosteroid and anesthetic modulation, and causes spontaneous channel opening. Little is known, however, about how epsilon affects receptor kinetics, which in turn shape responses to both ambient and synaptic GABA exposure. Here, we expressed human alpha2beta1, alpha2beta1gamma2, or alpha2beta1epsilon subunit combinations in human embryonic kidney 293 cells and used rapid solution exchange to study receptor kinetics in outside-out patches. The epsilon subunit greatly slowed deactivation and recovery after brief GABA pulses. During long, saturating GABA pulses, the rate of desensitization was slower for alpha2beta1epsilon and alpha2beta1gamma2 than for alpha2beta1. However, in alpha2beta1epsilon, the final extent of desensitization was large compared with that of alpha2beta1gamma2. Responses in alpha2beta1epsilon, but not the others, were often followed by an "overshoot" above the baseline, suggesting that a fraction of channels are spontaneously open and are transiently silenced by receptor activation and subsequent desensitization. The baseline current and associated noise were reduced by picrotoxin, revealing that epsilon-containing channels are open approximately 4% of the time in the absence of GABA. These results suggest that, if epsilon-containing receptors are expressed at synapses, the synaptic currents would be long-lasting but may rundown quickly under high-frequency activation. In addition, silencing of spontaneous openings by desensitization raises the possibility that tonic inhibition mediated by epsilon-containing receptors may be regulated by phasic inhibition.

KW - Cell Line

KW - Dose-Response Relationship, Drug

KW - Dose-Response Relationship, Radiation

KW - Electric Stimulation/methods

KW - GABA Antagonists/pharmacology

KW - Humans

KW - Ion Channel Gating/drug effects

KW - Kinetics

KW - Membrane Potentials/drug effects

KW - Neural Inhibition/drug effects

KW - Patch-Clamp Techniques/methods

KW - Picrotoxin/pharmacology

KW - Probability

KW - Protein Subunits/physiology

KW - Receptors, GABA-A/genetics

KW - Synaptic Transmission/drug effects

KW - Time Factors

KW - Transfection/methods

KW - gamma-Aminobutyric Acid/pharmacology

U2 - 10.1523/JNEUROSCI.1658-05.2005

DO - 10.1523/JNEUROSCI.1658-05.2005

M3 - Article

VL - 25

SP - 10462

EP - 10468

JO - Journal of Neuroscience

JF - Journal of Neuroscience

SN - 0270-6474

IS - 45

ER -