title: Bilayers merge even when exocytosis is transient.
abstract: During exocytosis, the lumen of secretory vesicles connects with the extracellular space. In some vesicles, this connection closes again, causing the vesicle to be recaptured mostly intact. The degree to which the bilayers of such vesicles mix with the plasma membrane is unknown. Work supporting the kiss-and-run model of transient exocytosis implies that synaptic vesicles allow neither lipid nor protein to escape into the plasma membrane, suggesting that the two bilayers never merge. Here, we test whether neuroendocrine granules behave similarly. Using two-color evanescent field microscopy, we imaged the lipid probe FM4-64 and fluorescent proteins in single dense core granules. During exocytosis, granules lost FM4-64 into the plasma membrane in small fractions of a second. Although FM4-64 was lost, granules retained the membrane protein, GFP-phogrin. By using GFP-phogrin as a probe for resealing, it was found that even granules that reseal lose FM4-64. We conclude that the lipid bilayers of the granule and the plasma membrane become continuous even when exocytosis is transient.
authors.affiliation: Vollum Institute, Oregon Health and Sciences University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239, USA.
authors.forename: Justin W
authors.initials: JW
authors.lastname: Taraska
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Almers
mesh_terms: D000818:Animals; D005089:Exocytosis / Q000502:physiology*; D005456:Fluorescent Dyes; D049452:Green Fluorescent Proteins; D008051:Lipid Bilayers / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008959:Models, Neurological; D009474:Neurons / Q000378:metabolism; D016716:PC12 Cells; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D051381:Rats; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism
chemical_list: C092350:FM 4-64; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; C102889:PTPRN2 protein, human; D017027:Protein Tyrosine Phosphatases; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8