Endogenous regulators of G protein signaling proteins regulate presynaptic inhibition at rat hippocampal synapses.
Presynaptic inhibition 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 of Galpha subunits alone. Here, we test the hypothesis that endogenous regulators of G protein signaling (RGS proteins) are required for rapid, brief presynaptic inhibition. Endogenous G protein alpha subunits were uncoupled from GPCRs by treating cultures with pertussis toxin (PTX). Adenoviral expression of mutant PTX-insensitive (PTX-i) Galpha(i1-3) or Galpha(o) subunits rescued adenosine-induced presynaptic inhibition in cultured hippocampal neurons. Expression of double mutant Galpha(i1) or Galpha(o) 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 of presynaptic inhibition mediated by PTX/RGS-i Galpha(o) was also slower than that mediated by PTX-i Galpha(o). In contrast, the onset of presynaptic inhibition mediated by PTX/RGS-i Galpha(i1) was similar to that mediated by PTX-i Galpha(i1). These results suggest that endogenous RGS proteins regulate the time course of G protein signaling in mammalian central nervous system presynaptic terminals.
Chen
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Department of Pharmacology and Toxicology, Medical College of Georgia, and Medical Research Service, Veterans Affairs Medical Center, Augusta, GA 30912, USA.
Lambert
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D000256:Adenoviridae; D000818:Animals; D002478:Cells, Cultured; D020555:GTP-Binding Protein Regulators / Q000235:genetics / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005822:Genetic Vectors; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology; D009433:Neural Inhibition; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D037342:Pertussis Toxin; D017729:Presynaptic Terminals / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000235:genetics / Q000378:metabolism
D020555:GTP-Binding Protein Regulators; D011993:Recombinant Fusion Proteins; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins