title: Neuronal peptide release is limited by secretory granule mobility.
abstract: Neuropeptides are slowly released from a limited pool of secretory granules. To visualize this process, GFP-tagged preproatrial natriuretic factor (ANF) was expressed in nerve growth factor-treated PC12 cells. Biochemical and microfluorimetric experiments demonstrate that proANF-EGFP is packaged in granules that accumulate at neurite endings and is released in a Ca2+-dependent manner by secretagogs. Confocal microscopy shows that secretion is associated with depletion of granules distributed throughout the terminal. Fluorescence recovery after photobleaching and time-lapse particle tracking reveal that only a subpopulation of cytoplasmic secretory granules, similar in size to the releasable pool, can move quickly enough (D = 6 x 10(-11) cm2/s) to support release. Therefore, sustained secretory responses are limited by the number of mobile granules and their slow rate of diffusion.
authors.affiliation: Department of Pharmacology, University of Pittsburgh, Pennsylvania 15261, USA.
authors.forename: N V
authors.initials: NV
authors.lastname: Burke
authors.forename: W
authors.initials: W
authors.lastname: Han
authors.forename: D
authors.initials: D
authors.lastname: Li
authors.forename: K
authors.initials: K
authors.lastname: Takimoto
authors.forename: S C
authors.initials: SC
authors.lastname: Watkins
authors.forename: E S
authors.initials: ES
authors.lastname: Levitan
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000502:physiology*; D004058:Diffusion; D005453:Fluorescence; D014644:Genetic Variation; D049452:Green Fluorescent Proteins; D007700:Kinetics; D008164:Luminescent Proteins / Q000235:genetics; D009474:Neurons / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D016716:PC12 Cells; D011498:Protein Precursors / Q000378:metabolism; D051381:Rats; D016324:Sequence Tagged Sites; D013268:Stimulation, Chemical; D014018:Tissue Distribution
chemical_list: D008164:Luminescent Proteins; D009479:Neuropeptides; D011498:Protein Precursors; D049452:Green Fluorescent Proteins; D009320:Atrial Natriuretic Factor