IONIC PERMEABILITY ON ISOLATED MOUSE-LIVER NUCLEI - INFLUENCE OF ATP AND CA2+

Patch-clamp experiments on isolated nuclei revealed the existence of i onic channels on the nuclear envelope, but their exact localization an d function are still unknown. Recent studies have demonstrated that AT P and calcium ions play an important role in nucleocytoplasmic protein traffic. ATP is essential to allow big molecules in and out of the nu cleus. However, a cytoplasmic rise of calcium ions above 300 nM decrea ses both ATP-dependent transport and passive diffusion through the nuc lear envelope. The use of isolated nuclei placed in a saline solution provides the possibility for testing only the compounds added in the b ath or in the recording pipette. In the present study, we show that AT P is responsible for an increase of nuclear ionic permeability on isol ated nuclei. This result not only confirms data previously reported in in situ nuclei, but also suggests that ATP is directly involved in th e modulation of passive ionic permeability. In these particular experi mental conditions, calcium ions decrease the channel current starting from a concentration of 1 mu M. The parallelism in the modulation acti on of ATP and Ca++ between nuclear pores and ionic channels present on the nuclear envelope contributes to the support of the idea that an i onic pathway is associated with the pore complex.