title: Nuclear envelope acts as a calcium barrier in C6 glioma cells.
abstract: The temporal and spatial changes of intracellular free calcium ([Ca2+]i) within the cytosol and nucleis of C6 glioma cells have been investigated with laser confocal scanning microscopy to evaluate the current view that Ca2+ ions pass freely through nuclear pores by diffusion. Our results indicate that localized cytosolic Ca2+ release, which appeared as puffs, spread with an apparent diffusion rate of 0.35 +/- 0.07 microns/sec (n = 44). This release was followed by an immediate Ca2+ uptake at the resting stage. Following the treatment with thapsigargin, an inhibitor of microsomal Ca(2+)-ATPase, release of nuclear Ca2+ from certain nuclear hot zones and nuclear envelope was obtained. Most of the nuclear Ca2+ released were confined to the nuclear boundary, but a slow migration of Ca2+ towards the cytosol was observed. The apparent diffusion rate of this Ca2+ release is 0.015 microns/sec. By contrast, the inward spread into nucleus occurred with a diffusion rate of 0.04 microns/sec. From these diffusion rates and other experimental evidence, we conclude that the movement of Ca2+ at the nucleocytosolic interface is more than a simple diffusion process and the interface is a barrier to Ca2+ movement.
authors.affiliation: Department of Biochemistry, Chinese University of Hong Kong, Shatin, NT, Hong Kong.
authors.forename: S K
authors.initials: SK
authors.lastname: Kong
authors.forename: D
authors.initials: D
authors.lastname: Tsang
authors.forename: K N
authors.initials: KN
authors.lastname: Leung
authors.forename: C Y
authors.initials: CY
authors.lastname: Lee
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002451:Cell Compartmentation; D004058:Diffusion; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005910:Glioma; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009685:Nuclear Envelope / Q000378:metabolism*; D051381:Rats; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured
chemical_list: D004791:Enzyme Inhibitors; D013729:Terpenes; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium