CALCIUM-RELEASE FROM THE NUCLEUS BY INSP(3) RECEPTOR CHANNELS

The nucleus is surrounded by a double membrane separating it from the cytoplasm. The perinuclear space is continuous with endoplasmic reticulum, and the nuclear outer membrane shares many features with the reticular membrane. We now show that inositol 1,4,5-trisphosphate (InsP(3)) receptors associated with the nucleus release Ca2+ from isolated Xeno pus laevis oocyte nuclei. Electrophysiological measurements of the intracellular InsP(3) receptor in its native membrane have not been possible on the fine filamentous endoplasmic reticulum. In this paper, we directly measure InsP(3)-dependent receptor channels in isolated nuclei. The nuclear InsP(3) receptor is activated by InsP(3) and modulated by Ca2+. The channel is weakly regulated by ATP, is mildly voltage dependent, and has a greater conductance with monovalent cations than with divalent cations.