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

Abstract

Heterotrimeric G-proteins at the plasma membrane serve as switches between heptahelical receptors and intracellular signal cascades. Likewise endomembrane associated G-proteins may transduce signals from intracellular compartments provided they consist of a functional trimer. Using quantitative immunoelectron microscopy we found heterotrimeric G-protein subunits Gαo2, Gαq/11 Gβ2 and Gβ5 to reside on secretory granules in chromaffin cells of rat adrenal glands.Thus rat chromaffin granules are equipped with functional G-proteins that consist of a specific α-, β- and probably γ-subunit combination. Serotonin uptake into a crude rat chromaffin granule preparation was inhibited by activated Gαo2 (10 nM) to nearly the same extent as by GMppNp (50 μM) whereas GDPβS was ineffective. The data support the idea that vesicular G-proteins directly regulate the transmitter content of secretory vesicles. In this respect Gαo2 appears to be the main regulator of vesicular momoamine transporter activity.