title: Acidification of serotonin-containing secretory vesicles induced by a plasma membrane calcium receptor.
abstract: Parafollicular (PF) cells secrete 5-hydroxytryptamine in response to increased extracellular Ca2+ ([Ca2+]e). This stimulus causes Cl- channels in PF secretory vesicles to open, leading to vesicle acidification. PF cells express a plasmalemmal heptahelical receptor (CaR) that binds Ca2+, Gd3+, and Ba2+. We now report that the CaR mediates vesicle acidification. Ca2+, Gd3+, and Ba2+ induced vesicle acidification, which was independent of channel-mediated Ca2+ entry. Agonist-induced vesicle acidification was blocked by pertussis toxin, inhibitors of phosphatidylinositol-phospholipase C, calmodulin, NO synthase, guanylyl cyclase, or protein kinase G. PF cells contained NO synthase immunoreactivity, and vesicles were acidified by NO donors and dibutyryl cGMP. [Ca2+]e, and Gd3+ mobilized thapsigargin-sensitive internal Ca2+ stores. [35S]G alpha i and [35S]G alpha q were immunoprecipitated from PF membranes incubated with agonists in the presence of [35S]adenosine 5'-O-(thiotriphosphate). Labeling of G alpha i but not G alpha q was antagonized by pertussis toxin. Vesicles acidified in response to activation of protein kinase C; however, protein kinase C inhibition blocked calcium channel- but not CaR-dependent acidification. We propose the following signal transduction pathway: CaR -> Gi -> phosphatidylinositol-phospholipase C -> inositol 1,4,5-trisphosphate -> [Ca2+]i -> Ca2+/calmodulin -> NO synthase -> NO -> guanylyl cyclase -> cGMP -> protein kinase G -> opens vesicular Cl- channel.
authors.affiliation: Division of Neuroscience, New York State Psychiatric Institute, New York 10032, USA.
authors.forename: H
authors.initials: H
authors.lastname: Tamir
authors.forename: K P
authors.initials: KP
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Adlersberg
authors.forename: S C
authors.initials: SC
authors.lastname: Hsiung
authors.forename: M D
authors.initials: MD
authors.lastname: Gershon
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism*; D005682:Gadolinium / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008954:Models, Biological; D009490:Neurosecretory Systems / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000819:agonists / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D012756:Sheep; D015398:Signal Transduction / Q000502:physiology; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*
chemical_list: D011956:Receptors, Cell Surface; D001464:Barium; D012701:Serotonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D005682:Gadolinium; D011493:Protein Kinase C; D002118:Calcium