title: Cytochemical localization of calcium in prefusion myoblasts from the chick embryo myotome.
abstract: Myoblast fusion is a Ca2+-dependent process. The aim of this report was to study the localization of Ca2+ in prefusion myoblasts from the brachial somites of chick embryos (51-108 h of incubation), using the potassium pyroantimonate cytochemical method. When observed under a transmission electron microscope, electron-dense precipitates of Ca2+-antimonate were found in the basement membrane of the myotome, which separates the myotome from the adjacent mesenchyma. Within myoblasts, triads and sarcoplasmic reticulum associated with the first newly formed sarcomeres were observed, but a T-tubule network was not found. Moreover, Ca2+-antimonate precipitates were not observed in structures resembling T-tubules or sarcoplasmic reticulum. The results suggest that sarcomerogenesis and sarcoplasmic reticulum development occur simultaneously and that prefusion myoblasts have neither a T-tubule network nor Ca2+ deposits on sarcoplasmic reticulum. Small Ca2+ pools were found in the myoblast nuclei, cytoplasmic vesicles and mitochondrias. Ca2+-antimonate precipitates periodically distributed at the cell periphery, close to the cell membrane, were observed. These precipitates could represent internal Ca2+ stores located in the peripheral couplings and it is proposed that these pools of Ca2+ could be mobilized before fusion, leading to the increase in free intracellular Ca2+ that precedes myoblast fusion.
authors.affiliation: Department of Morphological Sciences and Surgery, University of Alcala, Madrid, Spain.
authors.forename: M V
authors.initials: MV
authors.lastname: Lobo
authors.forename: R G
authors.initials: RG
authors.lastname: Santander
authors.forename: G M
authors.initials: GM
authors.lastname: Cuadrado
authors.forename: F J
authors.initials: FJ
authors.lastname: Alonso
mesh_terms: D000818:Animals; D000965:Antimony; D001485:Basement Membrane / Q000737:chemistry / Q000196:embryology / Q000648:ultrastructure; D002118:Calcium / Q000032:analysis*; D002614:Chelating Agents / Q000494:pharmacology; D002642:Chick Embryo / Q000737:chemistry* / Q000166:cytology / Q000648:ultrastructure; D004396:Coloring Agents; D004492:Edetic Acid / Q000494:pharmacology; D005110:Extracellular Space; D006651:Histocytochemistry / Q000379:methods; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology* / Q000648:ultrastructure; D009132:Muscles / Q000737:chemistry / Q000196:embryology; D012518:Sarcomeres / Q000737:chemistry; D012519:Sarcoplasmic Reticulum / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D004396:Coloring Agents; C009002:potassium antimonate; D004492:Edetic Acid; D000965:Antimony; D002118:Calcium