title: Neurohormone secretion persists after post-afterdischarge membrane depolarization and cytosolic calcium elevation in peptidergic neurons in intact nervous tissue.
abstract: The purpose of this work was to test the hypothesis that an electrical afterdischarge (AD) causes prolonged elevation in cytosolic calcium levels that is associated with prolonged secretion of egg-laying hormone (ELH) from peptidergic neurons in intact nervous tissue of Aplysia. Using a combination of radioimmunoassay measurement of ELH secretion, electrophysiological measurement of membrane potential, and optical imaging of the concentration of intracellular free calcium ions ([Ca2+]i), we verified that there was persistent secretion of ELH after the end of the AD; this was accompanied by prolonged post-AD membrane depolarization and prolonged post-AD elevation in [Ca2+]i. Extracellular treatment with the calcium chelator EGTA had no effect on the pattern or magnitude of ELH secretion or on the post-AD membrane potential (V(m)) and post-AD Ca2+ signal, ruling out a role for extracellular calcium in the post-AD elevation of [Ca2+]i. Both V(m) and [Ca2+]i returned to baseline well before ELH secretion, such that neither prolonged membrane depolarization nor prolonged Ca2+ signaling can fully account for the extent of the persistent secretion of ELH. These findings suggest a unique relationship between membrane excitability, Ca2+ signaling, and prolonged neuropeptide secretion.
authors.affiliation: Department of Physiology, David Geffin School of Medicine at University of California at Los Angeles, Los Angeles, California 90095, USA.
authors.forename: Stephan
authors.initials: S
authors.lastname: Michel
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Wayne
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001048:Aplysia; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D004558:Electric Stimulation; D004594:Electrophysiology; D005089:Exocytosis; D005456:Fluorescent Dyes; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000502:physiology; D066298:In Vitro Techniques; D007447:Invertebrate Hormones / Q000378:metabolism; D008845:Microinjections; D016501:Neurites / Q000378:metabolism; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D007447:Invertebrate Hormones; D018377:Neurotransmitter Agents; C026880:egg-laying hormone, Mollusca; D002118:Calcium