title: The localization of sodium and calcium to schwann cell paranodal loops at nodes of Ranvier and of calcium to compact myelin.
abstract: High-voltage electron microscopy (HVEM) has been used to determine the distribution of cationic precipitates in myelinated axons resulting from the application of two cytochemical techniques: a direct osmium pyroantimonate treatment for precipitating Na+, Ca2+ and Mg2+; and a 5 mM Ca2+ inclusion procedure (Oschman & Wall) for imparting electron density to Ca2+ binding sites. Electron probe wavelength spectroscopy was then used on semi-thick tissue sections to identify the species of ions present in the following regions: Schwann cell paranodal loops, axoplasm at the node, compact myelin and extracellular matrix. With these combined procedures we were able to localize elevated concentrations of both Na+ and Ca2+ to cytoplasmic compartments of the Schwann cell paranodal loops, as well as to detect the presence of Ca2+ at elevated levels in compact myelin. The involvement of the Schwann cell paranodal loops in providing a source and/or sink for Na+ involved in impulse conduction is suggested by these results, and the significance of such a role is discussed. A role for Ca2+ in the formation and stabilization of myelin lamellae is also suggested.
mesh_terms: D000818:Animals; D001369:Axons / Q000032:analysis; D002118:Calcium / Q000032:analysis*; D003593:Cytoplasm / Q000032:analysis; D009186:Myelin Sheath / Q000032:analysis* / Q000648:ultrastructure; D011901:Ranvier's Nodes / Q000032:analysis* / Q000648:ultrastructure; D051381:Rats; D012583:Schwann Cells / Q000032:analysis* / Q000648:ultrastructure; D012964:Sodium / Q000032:analysis*
chemical_list: D012964:Sodium; D002118:Calcium