title: The vesicular monoamine content regulates VMAT2 activity through Galphaq in mouse platelets. Evidence for autoregulation of vesicular transmitter uptake.
abstract: Variations in the neurotransmitter content of secretory vesicles enable neurons to adapt to network changes. Vesicular content may be modulated by vesicle-associated Go(2), which down-regulates the activity of the vesicular monoamine transmitter transporters VMAT1 in neuroendocrine cells and VMAT2 in neurons. Blood platelets resemble serotonergic neurons with respect to transmitter storage and release. In streptolysin O-permeabilized platelets, VMAT2 activity is also down-regulated by the G protein activator guanosine 5'-(beta(i)gamma-imido)triphosphate (GMppNp). Using serotonin-depleted platelets from peripheral tryptophan hydroxylase knockout (Tph1-/-) mice, we show here that the vesicular filling initiates the G protein-mediated down-regulation of VMAT2 activity. GMppNp did not influence VMAT2 activity in naive platelets from Tph1-/- mice. GMppNp-mediated inhibition could be reconstituted, however, when preloading Tph1-/- platelets with serotonin or noradrenaline. Galpha(q) mediates the down-regulation of VMAT2 activity as revealed from uptake studies performed with platelets from Galpha(q) deletion mutants. Serotonergic, noradrenergic, as well as thromboxane A(2) receptors are not directly involved in the down-regulation of VMAT2 activity. It is concluded that in platelets the vesicle itself regulates transmitter transporter activity via its content and vesicle-associated Galpha(q).
authors.affiliation: Institut für Anatomie der Charité, Humboldt Universität zu Berlin, Philippstrasse 12, 10115 Berlin, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Höltje
authors.forename: Sandra
authors.initials: S
authors.lastname: Winter
authors.forename: Diego
authors.initials: D
authors.lastname: Walther
authors.forename: Ingrid
authors.initials: I
authors.lastname: Pahner
authors.forename: Heide
authors.initials: H
authors.lastname: Hörtnagl
authors.forename: Ole Petter
authors.initials: OP
authors.lastname: Ottersen
authors.forename: Michael
authors.initials: M
authors.lastname: Bader
authors.forename: Gudrun
authors.initials: G
authors.lastname: Ahnert-Hilger
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D005260:Female; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000502:physiology*; D006706:Homeostasis; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D009479:Neuropeptides; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000502:physiology; D022142:Secretory Vesicles / Q000737:chemistry / Q000502:physiology*; D012701:Serotonin / Q000032:analysis / Q000378:metabolism*; D014365:Tryptophan Hydroxylase / Q000502:physiology; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins
chemical_list: D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009479:Neuropeptides; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; C493450:Slc18a1 protein, mouse; C493453:Slc18a2 protein, mouse; D050492:Vesicular Biogenic Amine Transport Proteins; D050493:Vesicular Monoamine Transport Proteins; D012701:Serotonin; D006165:Guanylyl Imidodiphosphate; D014365:Tryptophan Hydroxylase; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins