title: Modulation of neurotransmission by GPCRs is dependent upon the microarchitecture of the primed vesicle complex.
abstract: G(i/o)-protein-coupled receptors (GPCRs) ubiquitously inhibit neurotransmission, principally via Gβγ, which acts via a number of possible effectors. GPCR effector specificity has traditionally been attributed to Gα, based on Gα's preferential effector targeting in vitro compared with Gβγ's promiscuous targeting of various effectors. In synapses, however, Gβγ clearly targets unique effectors in a receptor-dependent way to modulate synaptic transmission. It remains unknown whether Gβγ specificity in vivo is due to specific Gβγ isoform-receptor associations or to spatial separation of distinct Gβγ pathways through macromolecular interactions. We thus sought to determine how Gβγ signaling pathways within axons remain distinct from one another. In rat hippocampal CA1 axons, GABA(B) receptors (GABA(B)Rs) inhibit presynaptic Ca(2+) entry, and we have now demonstrated that 5-HT(1B) receptors (5-HT(1B)Rs) liberate Gβγ to interact with SNARE complex C terminals with no effect on Ca(2+) entry. Both GABA(B)Rs and 5-HT(1B)Rs inhibit Ca(2+)-evoked neurotransmitter release, but 5-HT(1B)Rs have no effect on Sr(2+)-evoked release. Sr(2+), unlike Ca(2+), does not cause synaptotagmin to compete with Gβγ binding to SNARE complexes. 5-HT(1B)Rs also fail to inhibit release following cleavage of the C terminus of the SNARE complex protein SNAP-25 with botulinum A toxin. Thus, GABA(B)Rs and 5-HT(1B)Rs both localize to presynaptic terminals, but target distinct effectors. We demonstrate that disruption of SNARE complexes and vesicle priming with botulinum C toxin eliminates this selectivity, allowing 5-HT(1B)R inhibition of Ca(2+) entry. We conclude that receptor-effector specificity requires a microarchitecture provided by the SNARE complex during vesicle priming.
authors.affiliation: Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois 60607 and Department of Pharmacology, Vanderbilt University Medical School, Nashville, Tennessee 37232.
authors.forename: Edaeni
authors.initials: E
authors.lastname: Hamid
authors.forename: Emily
authors.initials: E
authors.lastname: Church
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Wells
authors.forename: Zack
authors.initials: Z
authors.lastname: Zurawski
authors.forename: Heidi E
authors.initials: HE
authors.lastname: Hamm
authors.forename: Simon
authors.initials: S
authors.lastname: Alford
mesh_terms: D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology*; D008297:Male; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*; D050600:SNARE Proteins / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000502:physiology
chemical_list: D043562:Receptors, G-Protein-Coupled; D050600:SNARE Proteins