title: Differential labelling of bulk endocytosis in nerve terminals by FM dyes.
abstract: Bulk endocytosis is triggered in central nerve terminals during intense physiological stimulation. This endocytosis pathway can be labelled by the dye FM1-43 but not its more hydrophilic counterpart FM2-10. This selective labelling was proposed to be due to the retention of FM1-43, but not FM2-10, in slowly retrieving structures after washout of the dye. However, this explanation assumed that bulk endocytosis was a slow process that persisted after stimulation. We have recently shown that the great majority of bulk endocytosis occurs during stimulation, therefore another explanation for the specific labelling of this pathway by FM1-43 must be found. In this paper we show that the ability of FM dyes to label bulk endocytosis is dependent on the concentration of dye used and not their washout properties. When the loading concentration of FM1-43 was reduced 10-fold, its ability to label bulk endocytosis was lost. Conversely when the loading concentration of FM2-10 was increased 10-fold, it now labelled the pathway. This suggests that a difference in affinity of bulk endosome membranes for FM1-43 and FM2-10 underlies the disparity in labelling.
authors.affiliation: Membrane Biology Group, Centre for Integrative Physiology, George Square, University of Edinburgh, Scotland, UK. E.L.Clayton@sms.ed.ac.uk
authors.forename: E L
authors.initials: EL
authors.lastname: Clayton
authors.forename: M A
authors.initials: MA
authors.lastname: Cousin
mesh_terms: D000818:Animals; D001370:Axonal Transport / Q000502:physiology; D002478:Cells, Cultured; D002490:Central Nervous System / Q000502:physiology* / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism* / Q000493:pharmacokinetics; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000502:physiology* / Q000648:ultrastructure; D011726:Pyridinium Compounds / Q000378:metabolism / Q000493:pharmacokinetics; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013194:Staining and Labeling / Q000379:methods*; D009435:Synaptic Transmission / Q000502:physiology; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism
chemical_list: C073804:FM1 43; C086686:FM2 10; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds