ATP-DEPENDENT IONIC PERMEABILITY ON NUCLEAR-ENVELOPE IN IN-SITU NUCLEI OF XENOPUS-OOCYTES

The nuclear envelope represents a structural and functional barrier be tween cytoplasm and nucleoplasm. Small molecules and solutes passively cross the nuclear envelope, whereas the transport of large proteins a nd RNA requires metabolic energy. Using in situ Xenopus oocyte nuclei, we characterized ATP-dependent ionic permeabilities on the external s urface of the envelope. The presence, but not necessarily the hydrolys is, of ATP is crucial to maintaining the channels in an open state. Lo calization of the ionic channels is still unclear. From morphologic an d current kinetics data, we suggest a relation between the ionic chann els and the nuclear pores. We try, in this way, to explain the apparen t contradiction between the presence of ion-selective channels in para llel with large aqueous pores on the nuclear envelope. Under this hypo thesis, variations in the metabolic energy content of the cytoplasm wo uld induce nucleocytoplasmic passive exchanges. The distribution and m ovement of charged particles across the nuclear envelope may influence many cytoplasmic functions. Regulation of the current by ATP could pl ay an important role in hormonal stimulation, divalent ion permeation into the nucleus, and cell cycle mechanisms.