ATP-dependent accumulation and inositol trisphosphate- or cyclic ADP-ribose-mediated release of Ca2+ from the nuclear envelope

Microscopic studies using fluorescent probes of the release and uptake of Ca2+ from cell nuclei in liver show that the Ca2+-sensitive fluorescent probe Fura 2 localizes mainly to the nuclear envelope, indicating that the inward and outward transport of Ca2+ from the nuclear envelope is responsible for the inositol triphosphate-dependent secretion of Ca2+. Fluorescent Ca2+ indicator-tagged dextrans display a uniform distribution in the nucleoplasm, while variations in external Ca2+ alter the nucleoplasmic Ca2+ level. Ca2+ released from the nuclear envelope enters nucleoplasm and diffuses out through nuclear pore complexes.