title: Calcium uptake via endocytosis with rapid release from acidifying endosomes.
abstract: A number of specific cellular Ca2+ uptake pathways have been described in many different cell types [1] [2] [3]. The possibility that substantial quantities of Ca2+ could be imported via endocytosis has essentially been ignored, although it has been recognized that endosomes can store Ca2+ [4] [5]. Exocrine cells can release significant amounts of Ca2+ via exocytosis [6], so we have investigated the fate of Ca2+ taken up via endocytosis into endosomes. Ca2+-sensitive and H+-sensitive fluorescent probes were placed in the extracellular solution and subsequently taken up into fibroblasts by endocytosis. Confocal microscopy was used to assess the distribution of fluorescence intensity. Ca2+ taken up by endocytosis was lost from the endosomes within a few minutes, over the same period as endosomal acidification took place. The acidification was inhibited by reducing the extracellular Ca2+ concentration, and Ca2+ loss from the endosomes was blocked by bafilomycin (100 nM), a specific inhibitor of the vacuolar proton ATPase. Quantitative evaluation indicated that endocytosis causes substantial import of Ca2+ because of rapid loss from early endosomes.
authors.affiliation: MRC Secretory Control Research Group The Physiological Laboratory University of Liverpool Crown Street Liverpool L69 3BX UK.
authors.forename: J V
authors.initials: JV
authors.lastname: Gerasimenko
authors.forename: A V
authors.initials: AV
authors.lastname: Tepikin
authors.forename: O H
authors.initials: OH
authors.lastname: Petersen
authors.forename: O V
authors.initials: OV
authors.lastname: Gerasimenko
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D018942:Macrolides; D051379:Mice; D018613:Microscopy, Confocal; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors
chemical_list: D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D018942:Macrolides; C057620:bafilomycin A; D006180:Proton-Translocating ATPases; D002118:Calcium