The nuclear envelope of resting C6 glioma cells is able to release and uptake Ca2+ in the absence of chemical stimulation.
Many agonists evoke events in the cell nucleus through the control of Ca2+ signals. Recent studies using isolated nuclei have indicated that the nuclear envelope is a store for nuclear Ca2+. However, the release of Ca2+ directly from the nuclear envelope in living cells has never been reported. In the present study, we have investigated the changes of Ca2+ signals at the cyto-nucleoplasmic interface of rat C6 glioma cells using confocal microscopy. Digital imaging indicates that fluo-3, a Ca2+-sensitive fluorescent probe, was concentrated in or around the nuclear envelope. Our experiments also revealed that C6 cells at rest produced spontaneous Ca2+ spikes in the absence of chemical stimulation. The amplitude of the repetitive Ca2+ spikes was higher at the nuclear envelope than in the whole cell or cytosol. After image subtraction, circular rims of Ca2+ release and uptake were seen at the outer boundary of the nucleus. When the cells were treated with thapsigargin (2 muM), a specific Ca2+-ATPase inhibitor, a long-lasting Ca2+ release was observed at the nuclear envelope. Moreover, most of the released Ca2+ was directed inwardly to the nucleoplasm with little outward diffusion. Our results thus indicate: (1) that the nuclear envelope is a Ca2+ store that possesses the ability to discharge and sequestrate Ca2+; and (2) the Ca2+-releasing channels are present in the inner nuclear membrane.
Lui
P P
PP
Department of Biochemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
Kong
S K
SK
Tsang
D
D
Lee
C Y
CY
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000814:Aniline Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D005910:Glioma / Q000648:ultrastructure*; D018613:Microscopy, Confocal; D009685:Nuclear Envelope / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014966:Xanthenes
D000814:Aniline Compounds; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium