The nuclear envelope is a part of the endoplasmic reticulum big enough to be studied with the patch-clamp technique. A variety of ion channels in the outer nuclear membrane have been reported in different animal and plant cells (Mazzanti et al. 2001). Here I report for the first time the recording of ionic channels from the nuclear membranes of neurons. This is also the first report of patch-clamp recording from the inner nuclear membrane.

Thin cerebellar slices were prepared from the brains of 21- to 28-day-old male Wistar rats, killed by cervical dislocation. Cell bodies of the Purkinje and granule cells were collected from the slices and gently homogenised in solution containing (mM): 100 potassium gluconate, 50 KCl, 5 MgCl₂, 0.05 CaCl₂, 0.5 EGTA and 10 Hepes; pH 7.3. The homogenate was placed into a working chamber. The nuclei were allowed to attach to the glass bottom of the chamber and then washed from debris with the same solution, but without MgCl₂ and EGTA. Single ion channels were recorded from both nucleus-attached and excised patches of the outer and inner nuclear membranes with the patch-clamp technique. The patch electrode was filled with solution containing (mM): 150 KCl, 0.05 CaCl₂ and 10 Hepes; pH 7.3. Experiments were conducted at room temperature (19-22 °C).

Ionic channels were detected in the nuclear membranes of both Purkinje and granule cells. The major channel (21 out of 29 patches) found in the nuclear membranes of Purkinje neurons was a cation-selective channel with the slope conductance of 198 ± 7 pS (n = 21 patches). This channel was especially abundant in the inner nuclear membrane of Purkinje cells where each patch contained ▓ge│ 2 channels. In contrast, the most common channel of the nuclear membranes of granule cells was the anion-selective channel. The anion channel had multiple conductance states with the slope conductance of the most common substate being 46 ± 5 pS (n = 18 patches). The nuclear membranes of granule neurones also contained a cationic channel with the slope conductance of 53 ± 4 pS (n = 5 patches).

These data suggest that different types of neurons express different classes of nuclear ion channels. The exact physiological role of nuclear channels is unknown. The nuclear envelope is a Ca²⁺ store, which implies large ion currents through the nuclear membranes. It is reasonable to suggest that nuclear channels are involved in the ionic homeostasis in the organelle. The expression of distinct types of ion channels in the nuclei of Purkinje and granule cells suggests different mechanisms of ionic homeostasis regulation in the nuclei of different neurons.

This work was supported by the Wellcome Trust. I am grateful to R.C. Thomas for his department’s hospitality in Cambridge and for help with supplies.