LARGE-CONDUCTANCE CATION CHANNELS IN THE ENVELOPE OF NUCLEI FROM RAT CEREBRAL-CORTEX

Eucaryotic nuclei are surrounded by a double-membrane system enclosing a central cisterna which is continuous with the endoplasmic reticulum and serves as a calcium store for intracellular signaling. The envelo pe regulates protein and nucleic acid traffic between the nucleus and the cytoplasm via nuclear pores. These protein tunnels cross through b oth nuclear membranes and are permeable for large molecules. Surprisin gly, patch clamp recordings from isolated nuclei of different cell spe cies have revealed a high resistance of the envelope, enabling tight s eals and the resolution of single ion channel activity. Here we presen t for the first time single-channel recordings from nuclei prepared fr om neuronal tissue. Nuclei isolated from rat cerebral cortex displayed spontaneous long-lasting large conductances in the nucleus-attached m ode as well as in excised patches. The open times are in the range of seconds and channel activity increases with depolarization. The single -channel conductance in symmetrical K+ is 166 pS. The channels are sel ective for cations with P-K/P-Na = 2. They are neither permeable to, n or gated by Ca2+. Thus, neuronal tissue nuclei contain a large conduct ance ion channel selective for monovalent cations which may contribute to ionic homeostasis in the complex compartments surrounding these or ganelles.