The large-conductance ion channels in the nuclear envelope of central neurons.

Patch-clamp recording from the nuclear envelope of a variety of cells has revealed the presence of large-conductance ion channels. It has been argued that these channels are the channels of the nuclear pore complex for passive nucleo-cytoplasmic diffusion. Here we studied spontaneously active large-conductance ion channels in the nuclear envelope of cerebellar Purkinje neurons. These channels were selective for small monovalent cations and demonstrated clear voltage dependence. The channels recorded from the outer nuclear membrane were inhibited by positive potentials whereas the channels from the inner nuclear membrane were inhibited by negative potentials in the patch pipette. These data are compatible with the localization of the channels to the nuclear membrane. We conclude that these channels are not a part of the nuclear pore complex but provide a route for exchange of monovalent cations between the perinuclear space and the cytoplasm and the nucleoplasm.

Spontaneously active and InsP3-activated ion channels in cell nuclei from rat cerebellar Purkinje and granule neurones.

Increases in Ca(2+) concentration in the nucleus of neurones modulate gene transcription and may be involved in activity-dependent long-term plasticity, apoptosis, and neurotoxicity. Little is currently known about the regulation of Ca(2+) in the nuclei of neurones. Investigation of neuronal nuclei is hampered by the cellular heterogeneity of the brain where neurones comprise no more than 10% of the cells. The situation is further complicated by large differences in properties of different neurones. Here we report a method for isolating nuclei from identified central neurones. We employed this technique to study nuclei from rat cerebellar Purkinje and granule neurones. Patch-clamp recording from the nuclear membrane of Purkinje neurones revealed numerous large-conductance channels selective for monovalent cations. The nuclear membrane of Purkinje neurones also contained multiple InsP(3)- activated ion channels localized exclusively in the inner nuclear membrane with their receptor loci facing the nucleoplasm. In contrast, the nuclear membrane of granule neurones contained only a small number of mainly anion channels. Nuclear InsP(3) receptors (InsP(3)Rs) were activated by InsP(3) with EC(50) = 0.67 microm and a Hill coefficient of 2.5. Ca(2+) exhibited a biphasic effect on the receptors elevating its activity at low concentrations and inhibiting it at micromolar concentrations. InsP(3) in saturating concentrations did not prevent the inhibitory effect of Ca(2+), but strongly increased InsP(3)R activity at resting Ca(2+) concentrations. These data are the first evidence for the presence of intranuclear sources of Ca(2+) in neurones. Ca(2+) release from the nuclear envelope may amplify Ca(2+) transients penetrating the nucleus from the cytoplasm or generate Ca(2+) transients in the nucleus independently of the cytoplasm.