title: Potentiation of exocytosis by phospholipase C-coupled G-protein-coupled receptors requires the priming protein Munc13-1.
abstract: The vesicle priming protein Munc13-1 is regulated by diacylglycerol (DAG) and is therefore hypothesized to play a role in the control of neurotransmitter release by phospholipase C (PLC)-coupled receptors. We combined voltage-clamp recordings of voltage-gated Ca2+ channels (VGCCs) and high-resolution capacitance measurements to investigate the mechanism of receptor-mediated modulation of exocytosis in bovine chromaffin cells. Activation of endogenous H1 G(q)-protein-coupled receptors (G(q)PCRs) by histamine potentiated stimulus-coupled secretion despite concurrently inhibiting Ca2+ influx through VGCCs. Histamine increased the size of the readily releasable pool of vesicles and in particular a subpool of fusion-competent vesicles localized in close proximity to VGCCs. Pharmacological characterization showed that potentiation of exocytosis depended on the activation of PLC but not protein kinase C. Overexpression of wild-type Munc13-1 by adenoviral infection had no effect on histamine-induced potentiation per se, whereas DAG-insensitive Munc13-1(H567K) completely abolished it. This is the first endogenous mammalian G(q)PCR signaling pathway identified that engages Munc13-1 to increase stimulus-coupled secretion by recruiting vesicles to the immediately releasable pool. G(q)PCRs are therefore able to control exocytosis at the level of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex formation to produce rapid, short-term potentiation of the secretory output of neurons and endocrine cells.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Claudia S
authors.initials: CS
authors.lastname: Bauer
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Woolley
authors.forename: Anja G
authors.initials: AG
authors.lastname: Teschemacher
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Seward
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D009419:Nerve Tissue Proteins; D043562:Receptors, G-Protein-Coupled; C485548:UNC13B protein, human; D010738:Type C Phospholipases