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Updated: Aug 8, 2026

Quantifying Agonist Activity at G Protein-coupled Receptors
11:45

Quantifying Agonist Activity at G Protein-coupled Receptors

Published on: December 26, 2011

Subunit composition and functional properties of G-protein heterotrimers on rat chromaffin granules

Ingrid Pahner1, Markus Höltje, Sandra Winter

  • 1Institut für Anatomie/Neurowissenschaftliches Zentrum der Charité, Humboldt Universität zu Berlin, Germany.

European Journal of Cell Biology
|September 18, 2002
PubMed

Insights

Functional G-proteins are present on rat chromaffin granules, regulating serotonin uptake. Activated G-protein subunit Galphao2 specifically controls vesicular monoamine transporter activity, impacting transmitter content.

Area of Science:

  • Cell Biology
  • Neuroscience
  • Biochemistry

Background:

  • Heterotrimeric G-proteins link plasma membrane receptors to intracellular signaling.
  • Endomembrane-associated G-proteins may also transduce signals if functional trimers are present.

Purpose of the Study:

  • To investigate the presence and function of heterotrimeric G-proteins on secretory granules in rat adrenal chromaffin cells.
  • To determine the role of specific G-protein subunits in regulating neurotransmitter content within vesicles.

Main Methods:

  • Quantitative immunoelectron microscopy was employed to localize G-protein subunits on secretory granules.
  • In vitro assays assessed the effect of activated G-protein subunits on serotonin uptake in chromaffin granule preparations.

Main Results:

  • Heterotrimeric G-protein subunits (Galpha2, Galpha(q/11), Gbeta2, Gbeta5) were localized on secretory granules of rat chromaffin cells.
  • Activated Galphao2 significantly inhibited serotonin uptake into chromaffin granules, similar to a non-hydrolyzable GTP analog.
  • GDPbetaS, an inhibitor of G-protein function, was ineffective in altering serotonin uptake.

Conclusions:

  • Rat chromaffin granules possess functional heterotrimeric G-proteins, comprising specific alpha, beta, and likely gamma subunits.
  • Vesicular G-proteins directly regulate the transmitter content of secretory vesicles.
  • Galphao2 is identified as the primary regulator of vesicular monoamine transporter activity.

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