title: Functional ryanodine receptors in the membranes of neurohypophysial secretory granules.
abstract: Highly localized Ca(2+) release events have been characterized in several neuronal preparations. In mouse neurohypophysial terminals (NHTs), such events, called Ca(2+) syntillas, appear to emanate from a ryanodine-sensitive intracellular Ca(2+) pool. Traditional sources of intracellular Ca(2+) appear to be lacking in NHTs. Thus, we have tested the hypothesis that large dense core vesicles (LDCVs), which contain a substantial amount of calcium, represent the source of these syntillas. Here, using fluorescence immunolabeling and immunogold-labeled electron micrographs of NHTs, we show that type 2 ryanodine receptors (RyRs) are localized specifically to LDCVs. Furthermore, a large conductance nonspecific cation channel, which was identified previously in the vesicle membrane and has biophysical properties similar to that of an RyR, is pharmacologically affected in a manner characteristic of an RyR: it is activated in the presence of the RyR agonist ryanodine (at low concentrations) and blocked by the RyR antagonist ruthenium red. Additionally, neuropeptide release experiments show that these same RyR agonists and antagonists modulate Ca(2+)-elicited neuropeptide release from permeabilized NHTs. Furthermore, amperometric recording of spontaneous release events from artificial transmitter-loaded terminals corroborated these ryanodine effects. Collectively, our findings suggest that RyR-dependent syntillas could represent mobilization of Ca(2+) from vesicular stores. Such localized vesicular Ca(2+) release events at the precise location of exocytosis could provide a Ca(2+) amplification mechanism capable of modulating neuropeptide release physiologically.
authors.affiliation: Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655.
authors.forename: James M
authors.initials: JM
authors.lastname: McNally
authors.affiliation: Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655.
authors.forename: Edward E
authors.initials: EE
authors.lastname: Custer
authors.affiliation: Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655.
authors.forename: Sonia
authors.initials: S
authors.lastname: Ortiz-Miranda
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602.
authors.forename: Dixon J
authors.initials: DJ
authors.lastname: Woodbury
authors.affiliation: Department of Neuroscience and Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Susan D
authors.initials: SD
authors.lastname: Kraner
authors.affiliation: Department of Neuroscience and Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104 Department of Neuroscience and Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Salzberg
authors.affiliation: Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655 Jose.Lemos@umassmed.edu.
authors.forename: José R
authors.initials: JR
authors.lastname: Lemos
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D005089:Exocytosis / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D051379:Mice; D009479:Neuropeptides / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*
chemical_list: D009479:Neuropeptides; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium