Regulators of G Protein Signaling (RGS Proteins) Regulate Presynaptic Inhibition at Rat Hippocampal Synapses

Hdl Handle:
http://hdl.handle.net/10675.2/344459
Title:
Regulators of G Protein Signaling (RGS Proteins) Regulate Presynaptic Inhibition at Rat Hippocampal Synapses
Authors:
Chen, Huanmian
Abstract:
Presynaptic inhibition o f elicited neurotransmitter release mediated by G protein-coupled receptors (GPCRs) can develop and decay in a few seconds. This time course is too rapid to be accounted for by the intrinsic GTPase activity o f Ga subunits alone. Here we test the hypothesis that endogenous regulators o f G protein signaling (RGS proteins), which are GTPase activating proteins (GAPs) for Ga, are required for rapid, brief presynaptic inhibition. Endogenous G protein a subunits were uncoupled from GPCRs by treating hippocampal microisland cultures with pertussis toxin (PTX). Adenovirusmediated expression o f mutant PTX-insensitive (PTX-i) Gau.3 or Ga0 subunits rescued adenosine-induced presynaptic inhibition in neurons. Expression o f double mutant Gan or Ga0 subunits that were both PTX-insensitive and unable to bind RGS proteins (PTX/RGS-i) also rescued presynaptic inhibition. Presynaptic inhibition mediated by PTX/RGS-i subunits decayed much more slowly after agonist removal than that mediated by PTX-i subunits or native G proteins. The onset o f presynaptic inhibition mediated by PTX/RGS-i Ga0 was also slower than that mediated by PTX-i Ga0. In contrast, the onset o f presynaptic inhibition mediated by PTX/RGS-i Gan was similar to that mediated by PTX-i Gan. These results suggest that endogenous RGS proteins are present in presynaptic terminals and essential for fast recovery o f presynaptic inhibition. The effect o f endogenous RGS proteins on the onset o f presynaptic inhibition appears dependent on the particular Ga subunits involved. We also performed experiments to test whether the functions o f RGS proteins are sensitive to upregulation. Over-expression o f RGS8 in neurons without pretreatment o f PTX not only accelerated the time course o f the onset but also increased the steady state level o f presynaptic inhibition. Overexpression o f RGS4 also enhanced the steady state. These results suggest that RGS8 and probably RGS4 as well can be transported to presynaptic terminals and upregulate the activation o f Gy0 protein signaling. Interestingly, overexpression o f these RGS proteins failed to accelerate the recovery o f presynaptic inhibition, although it is well established that both RGS8 and RGS4 are strong GAPs for GcCj/0. This result suggests GAP activity for Gai/0 in presynaptic terminals is physiologically “ saturated” by endogenous RGS proteins.
Affiliation:
Department of Pharmacology and Toxicology
Issue Date:
Nov-2000
URI:
http://hdl.handle.net/10675.2/344459
Additional Links:
http://ezproxy.gru.edu/login?url=http://search.proquest.com/docview/304733147?accountid=12365
Type:
Dissertation
Appears in Collections:
Theses and Dissertations

Full metadata record

DC FieldValue Language
dc.contributor.authorChen, Huanmianen
dc.date.accessioned2015-02-13T20:49:43Z-
dc.date.available2015-02-13T20:49:43Z-
dc.date.issued2000-11-
dc.identifier.urihttp://hdl.handle.net/10675.2/344459-
dc.description.abstractPresynaptic inhibition o f elicited neurotransmitter release mediated by G protein-coupled receptors (GPCRs) can develop and decay in a few seconds. This time course is too rapid to be accounted for by the intrinsic GTPase activity o f Ga subunits alone. Here we test the hypothesis that endogenous regulators o f G protein signaling (RGS proteins), which are GTPase activating proteins (GAPs) for Ga, are required for rapid, brief presynaptic inhibition. Endogenous G protein a subunits were uncoupled from GPCRs by treating hippocampal microisland cultures with pertussis toxin (PTX). Adenovirusmediated expression o f mutant PTX-insensitive (PTX-i) Gau.3 or Ga0 subunits rescued adenosine-induced presynaptic inhibition in neurons. Expression o f double mutant Gan or Ga0 subunits that were both PTX-insensitive and unable to bind RGS proteins (PTX/RGS-i) also rescued presynaptic inhibition. Presynaptic inhibition mediated by PTX/RGS-i subunits decayed much more slowly after agonist removal than that mediated by PTX-i subunits or native G proteins. The onset o f presynaptic inhibition mediated by PTX/RGS-i Ga0 was also slower than that mediated by PTX-i Ga0. In contrast, the onset o f presynaptic inhibition mediated by PTX/RGS-i Gan was similar to that mediated by PTX-i Gan. These results suggest that endogenous RGS proteins are present in presynaptic terminals and essential for fast recovery o f presynaptic inhibition. The effect o f endogenous RGS proteins on the onset o f presynaptic inhibition appears dependent on the particular Ga subunits involved. We also performed experiments to test whether the functions o f RGS proteins are sensitive to upregulation. Over-expression o f RGS8 in neurons without pretreatment o f PTX not only accelerated the time course o f the onset but also increased the steady state level o f presynaptic inhibition. Overexpression o f RGS4 also enhanced the steady state. These results suggest that RGS8 and probably RGS4 as well can be transported to presynaptic terminals and upregulate the activation o f Gy0 protein signaling. Interestingly, overexpression o f these RGS proteins failed to accelerate the recovery o f presynaptic inhibition, although it is well established that both RGS8 and RGS4 are strong GAPs for GcCj/0. This result suggests GAP activity for Gai/0 in presynaptic terminals is physiologically “ saturated” by endogenous RGS proteins.en
dc.relation.urlhttp://ezproxy.gru.edu/login?url=http://search.proquest.com/docview/304733147?accountid=12365en
dc.rightsCopyright protected. Unauthorized reproduction or use beyond the exceptions granted by the Fair Use clause of U.S. Copyright law may violate federal law.en
dc.subjectpresynaptic inhibitionen
dc.subjectRGS proteinsen
dc.subjectG proteinsen
dc.titleRegulators of G Protein Signaling (RGS Proteins) Regulate Presynaptic Inhibition at Rat Hippocampal Synapsesen
dc.typeDissertationen
dc.contributor.departmentDepartment of Pharmacology and Toxicologyen
dc.description.advisorLambert, Nevin A.en
dc.description.committeeNot Listeden
dc.description.degreeDoctor of Philosophy (Ph.D.)en
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