Ionic Coulomb blockade and the determinants of selectivity in the NaChBac bacterial sodium channel.

Mutation-induced transformations of conductivity and selectivity in NaChBac bacterial channels are studied experimentally and interpreted within the framework of ionic Coulomb blockade (ICB), while also taking account of resonant quantised dehydration (QD) and site protonation. Site-directed mutagenesis and whole-cell patch-clamp experiments are used to investigate how the fixed charge Qf at the selectivity filter (SF) affects both valence selectivity and same-charge selectivity. The new ICB/QD model predicts that increasing ∣Qf∣ should lead to a shift in selectivity sequences toward larger ion sizes, in agreement with the present experiments and with earlier work. Comparison of the model with experimental data leads to the introduction of an effective charge Qf∗ at the SF, which was found to differ between Aspartate and Glutamate charged rings, and also to depend on position within the SF. It is suggested that protonation of the residues within the restricted space of the SF is important in significantly reducing the effective charge of the EEEE ring. Values of Qf∗ derived from experiments on divalent blockade agree well with expectations based on the ICB/QD model and have led to the first demonstration of ICB oscillations in Ca2+ conduction as a function of the fixed charge. Preliminary studies of the dependence of Ca2+ conduction on pH are qualitatively consistent with the predictions of the model.

[The effect of Ca2+ on the properties of the large conductance cation channels of the nuclear envelope of the cerebellar neurons].

Previously we have found the large conductance cation channels (LCCC) in the nuclear membranes, where inositol-1,4,5-triphosphate receptors (IP3Rs) were also observed. Probably IP3Rs and LCCC are functionally connected: LCCC may provide the counterflow of K+, which prevent the formation of the negative potential in the lumen of the nuclear envelope and in such way may prolong the Ca2+ releasing by IP3Rs. LCCC are poorly studied and their molecular nature is still unknown. We investigated the effect of Ca2+ on properties of these channels. Our results demonstrated the main biophysical properties of LCCC changed significantly neither in Ca(2+)-free solution, nor with high concentrations of Ca2+ in the nuclear lumen. So, the level of Ca2+ repletion of the store does not influence the activity of LCCC.

[Spontaneously active ion channels of the nuclear envelope membrane].

The genetic apparatus of the eukaryotic cells is enclosed by the nuclear envelope, which consists of two membranes, the inner and the outer ones, and can be regarded as the specific part of the endoplasmatic reticulum of the cell. There are nuclear pores in the nuclear membranes--complexes, which provide the highly selective transport of macromolecules and passive transport of ions and small molecules. Besides, ion channels selective to cations and anions were described in the inner and the outer nuclear membranes. The physiological significance of these channels is not still clear because of the difficulty of access for the direct electrophysiological investigation, but we can suppose that they can play an important role in the ion balance between the cytoplasm/nucleoplasm and the nuclear lumen. In this review we gathered and analyzed data about spontaneously active ion channels which were found in the membranes of the nuclear envelope from cells of different types and tried to propose their functional meaning.

[Nuclear ion channels of the granular neurons from the dentate gyrus].

The nuclear envelope is a part of the endoplasmic reticulum which surrounds the genetic apparatus of the cell. Using the patch-clamp technique we have investigated ion channels in the membranes of nuclei isolated from the neurons of the dentate gyrus. Our research has shown that there is anionic (329 pS) on the outer and anionic (157 pS) and cationic (179 pS) channels on the inner nuclear membrane. Ion channels in the nuclear envelope of the neurons of the dentate gyrus differ much from ones of the neurons of the cerebellum and CA region of the hippocampus. This fact proves that different types of neurons express different sets of ion channels in the nuclear membranes. The physiological role of the ion nuclear channels in the granule cells is not clear but they may be important for the ion balance between the cytoplasm and the lumen of the nuclear envelope as well as endoplasmic reticulum of the cell if the latter represents an adequate model of granule of the some parts of ER.

[New cation channel of the T-lymphocyte nuclear membrane].

There are little data on the properties of ion channels in the inner nuclear membrane of lymphocytes, though the transport system between cytoplasm and karyoplasm is of a great importance for a complex genetic regulation in these cells. Using the patch-clamp technique we have investigated ion channels of the inner membrane of nuclei isolated from cultured T-lymphoblasts. Our research has shown that there are anionic (370 pS) and cationic (152 pS) channels on the inner nuclear membrane. The latter were characterized by fast kinetics and rapid fluctuations; they had high open probability and were inactivated at large negative potentials. These channels were permeable for K+ and Na+, but impermeable for Cl-. The physiological role of the channels is not clear, but they may play an important role in the ion balance between the cytoplasm and the lumen of the endoplasmatic reticulume of the cell.