title: Unexpected mobility variation among individual secretory vesicles produces an apparent refractory neuropeptide pool.
abstract: Most stored neuropeptide cannot be released from nerve terminals suggesting the existence of a refractory pool of dense core vesicles (DCVs). Past fluorescence photobleaching recovery, single particle tracking and release experiments suggested that the refractory neuropeptide pool corresponds to a distinct immobile fraction of cytoplasmic DCVs. However, tracking of hundreds of individual green fluorescent protein-labeled neuropeptidergic vesicles by wide-field or evanescent-wave microscopy shows that a separate immobile fraction is not evident. Instead, the DCV diffusion coefficient (D) distribution is unusually broad and asymmetric. Furthermore, the distribution shifts with a release facilitator. This unexpected variation, which could reflect heterogeneity among vesicles or in their medium, is shown to generate the appearance of a regulated refractory neuropeptide pool.
authors.affiliation: Department of Pharmacology, E1351 Biomedical Science Tower, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Yuen-Keng
authors.initials: YK
authors.lastname: Ng
authors.forename: Xinghua
authors.initials: X
authors.lastname: Lu
authors.forename: Alexandra
authors.initials: A
authors.lastname: Gulacsi
authors.forename: Weiping
authors.initials: W
authors.lastname: Han
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Saxton
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Levitan
mesh_terms: D000818:Animals; D002465:Cell Movement / Q000502:physiology*; D003198:Computer Simulation; D004058:Diffusion; D008856:Microscopy, Fluorescence / Q000379:methods*; D008954:Models, Biological; D009414:Nerve Growth Factors / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D016716:PC12 Cells; D021381:Protein Transport / Q000502:physiology*; D051381:Rats; D015203:Reproducibility of Results; D022142:Secretory Vesicles / Q000502:physiology* / Q000648:ultrastructure; D012680:Sensitivity and Specificity
chemical_list: D009414:Nerve Growth Factors; D009479:Neuropeptides