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The electron paramagnetic resonance (EPR) parameters (g factors [g.sub.[parallel]], [g.sup.[perpendicular]] and hyperfine structure constants [A.sub.[parallel]], [A.sub.[]]) and the local structure of the tetragonal [Cu.sup.2+] center in trigonal ZnSe[F.sub.6] x 6[H.sub.2]O crystal are theoretically investigated from the perturbation formulas of these parameters for a 3[d.sup.9] ion in tetragonally elongated octahedra. In the calculated formulas, the contributions to the EPR parameters from ligand orbital and spin-orbit coupling are included on the basis of the cluster approach in view of moderate covalency of the studied systems, the required crystal-field parameters are estimated from the superposition model, which enables correlation of the crystal-field parameters and hence the EPR parameters with the tetragonal distortion of the studied [[Cu[([H.sub.2]O).sub.6]].sup.2+] cluster. According to the calculations, the ligand octahedra around [Cu.sup.2+] are suggested to suffer relative elongation [tau] ([approximately equals] 0.085 [Angstrom]) along the [001] (or [C.sub.4]) axis for the tetragonal [Cu.sup.2+] centers in ZnSe[F.sub.6] x 6[H.sub.2]O crystal, due to the Jahn-Teller effect. The results are discussed. Key words: electron paramagnetic resonance (EPR), crystal fields, local structure, [Cu.sup.2+], ZnSe[F.sub.6] x 6[H.sub.2]O. Les parametres de resonance paramagnetique electronique (EPR) (les facteur g, [g.sub.[parallel]], [g.sub.[]], et les constantes de structure hyperfine [A.sub.[parallel]], [A.sub.[]]) et la structure locale du centre tetragonal [Cu.sup.2+] dans le cristal trigonal ZnSe[F.sub.6] x 6[H.sub.2] sont ici soumis a une etude theorique a partir des formules de perturbations de ces parametres pour un ion 3[d.sup.9] dans un octaedre allonge tetragonalement. Dans nos calculs, nous incluons les contributions aux parametres provenant des orbitales ligands et du couplage spin-orbite sur la base d'une approche cluster visant des systemes de covalence moderee. Nous estimons les parametres du champ cristallin a partir d'un modele de superposition qui permet les correlations des parametres du champ cristallin et nous etudions ainsi les parametres EPR avec la distorsion tetragonale du cluster etudie [[Cu[([H.sub.2]O).sub.6]].sup.2+]. Nos calculs suggerent que les ligands octaedres autour de [Cu.sup.2+] souffrent de la relative elongation [tau] ([approximately equals] 0.085 [Angstrom]) le long de [001], ou axe [C.sub.4], pour les centres tetragonaux [Cu.sup.2+] dans le cristal ZnSe[F.sub.6]-6[H.sub.2]O, a cause de l'effet Jahn-Teller. Nous analysons les resultats. [Traduit par la Redaction] Mots-cles: parametre de resonance paramagnetique electronique (EPR), champs cristallins, structure locale, [Cu.sup.2+], ZnSe[F.sub.6]-6[H.sub.2]O. PACS Nos.: 76.30.Fc, 71.70.Ch, 75.10.Dg, 71.70.Ej., 1. Introduction ZnM[F.sub.6] x 6[H.sub.2]O (M = Ge, Se, Si, Zr) belongs to the family of isostructural fluosilicate hexahydrates having CsCl-type structure with space group R[bar.3]. In these crystals, [Zn.sup.2+] [...]

Opiate addiction has a high rate of relapse. The accumulating evidence shows that electroacupuncture (EA) may be effective for the treatment of opiate relapse. However, the change of expression of CB1-Rs and CB2-Rs involve in 2Hz EA anti-relapse pathway is still unclear. To explore the changes of expression of CB1-Rs and CB2-Rs, heroin self-administration (SA) model rats were adopted and treated using 2Hz EA. The expressions of CB1-Rs and CB2-Rs were observed using immunohistochemistry method. The results showed that, compared with the control group, active pokes in the heroin-addicted group increased, while the active pokes decreased significantly in 2Hz EA group compared with heroin-addicted group. Correspondingly, the expression of CB1-Rs in prefrontal cortex (PFC), hippocampus (Hip), nucleus accumbens (NAc) and ventral tegmental area (VTA) all increased significantly while the expression of CB2-Rs in those relapse-relevant brain regions decreased obviously in heroin-addicted group when compared with the control group. In addition, the expression of CB1-Rs obviously decreased in the 2Hz EA group while the expression of CB2-Rs in those relapserelevant brain regions increased significantly when compared with the heroin-addicted group. It indicated that 2Hz EA could attenuate the heroin-evoked seeking behaviors effectively. The anti-relapse effects of 2Hz EA might be related to the decrease of CB1-Rs and increase of CB2-Rs expression in relapse-relevant brain regions of heroin SA rats. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters ( g factors g∥, g⊥ and hyperfine structure constants A∥, A⊥) and the local structure of the tetragonal Cu2+ center in trigonal ZnSeF6·6H2O crystal are theoretically investigated from the perturbation formulas of these parameters for a 3d9 ion in tetragonally elongated octahedra. In the calculated formulas, the contributions to the EPR parameters from ligand orbital and spin-orbit coupling are included on the basis of the cluster approach in view of moderate covalency of the studied systems, the required crystal-field parameters are estimated from the superposition model, which enables correlation of the crystal-field parameters and hence the EPR parameters with the tetragonal distortion of the studied [Cu(H2O)6]2+ cluster. According to the calculations, the ligand octahedra around Cu2+ are suggested to suffer relative elongation τ (≈ 0.085 Å) along the [001] (or C4) axis for the tetragonal Cu2+ centers in ZnSeF6·6H2O crystal, due to the Jahn-Teller effect. The results are discussed. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters [i.e. g factors g i ( i= x, y, z) and hyperfine structure constants A i] and the local lattice structure for the Cu2+ centre in Tl2Zn(SO4)2·6H2O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d9 ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu2+-H2O bond lengths are obtained as follows: R x≈1.98 Å, R y≈2.09 Å, R z≈2.32 Å. The results are discussed. [ABSTRACT FROM AUTHOR]

High-order perturbation formulas for a 3d9 ion in rhombically elongated octahedral was applied to calculate the electron paramagnetic resonance (EPR) parameters (the g factors, gi, and the hyperfine structure constants Ai, i = x, y, z) of the rhombic Cu2+ center in CoNH4PO4·6H2O. In the calculations, the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the local structure of the rhombic Cu2+ center. Based on the calculations, the ligand octahedral (i.e. [Cu(H2O)6]2+ cluster) are found to experience the local bond length variations ΔZ (≈0.213 Å) and δr (≈0.132 Å) along axial and perpendicular directions due to the Jahn–Teller effect. Theoretical EPR parameters based on the above local structure are in good agreement with the observed values; the results are discussed. [ABSTRACT FROM AUTHOR]

The spin-Hamiltonian parameters (the g factors gi and the hyperfine structure constants Ai, i = x, y, z) and local structure of the Cu2+ center in PbTiO3 are theoretically studied by using the perturbation formulae of these parameters for a 3d9 ion in an orthorhombically elongated octahedra. The orthorhombic center is attributed to Cu2+ occupying the host Ti4+ site associated with a nearest-neighbouring oxygen vacancy VO along the c-axis, and the impurity Cu2+ off-center displacement ΔZL (≈0.18 Å) is smaller than that of the host Ti4+ site (ΔZH ≈ 0.3 Å). Meanwhile, the planar Cu2+-O2- bonds are found to experience the relative variation ΔR (≈ 0.098 Å) along the a- and b-axes, respectively, due to the Jahn-Teller effect and the size mismatching substitution of Ti4+ by Cu2+. The theoretical spin-Hamiltonian parameters based on the above defect structure agree well with the observed values. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters (gfactorsgx,gy,gzand hyperfine structure constantsAx,Ay,Az) for Cu2+in (NH4)2Mg(SO4)2·6H2O (DHMS) crystal are theoretically investigated using the high-order perturbation formulas of these parameters. In the calculations, the ligand orbital and spin–orbit coupling for the impurity Cu2+are taken into account; the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the local structure of the impurity center. The ligand orbital and the spin–orbit coupling contributions are included on the basis of the cluster approach. Based on the calculation, the theoretical EPR parameters show good agreement with the observed values. The results are discussed. [ABSTRACT FROM AUTHOR]

One feature of the amino acid sequence of P2X receptors identified from mammalian species, Xenopus laevis and zebrafish is the conservation of ten cysteines in the extracellular loop. Little information is available about the role of these conserved ectodomain cysteines in the function of P2X receptors. Here, we investigated the possibility that ten conserved cysteine residues in the extracellular loop of the rat P2X4 receptor may regulate zinc potentiation of the receptor using a series of individual cysteine to alanine point mutations and functional characterization of recombinant receptors expressed in Xenopus oocytes. For the C116A, C132A, C159A, C165A, C217A and C227A mutants, 10µM zinc did not significantly affect the current activated by an EC40 concentration of ATP. By contrast, 5µM zinc shifted the ATP concentration-response curve to the right in a parallel manner for both the C261A and C270A mutants and the magnitudes of those shifts were similar to that of the wildtype receptor. Interestingly, for the C126A and C149A mutants, 5µM zinc potentiated ATP-activated current, but increased the maximal response to ATP by 90% and 81% respectively, without significantly changing the EC50 value of ATP. Thus, these results suggest that cysteines and disulfide bonds between cysteines are differentially involved in the potentiation of the rat P2X4 receptor by zinc. [ABSTRACT FROM AUTHOR]

Abstract: We have recently reported that bis(7)-tacrine could prevent glutamate-induced neuronal apoptosis through NMDA receptors. In this study, we demonstrated that in cultured rat cortical neurons, bis(7)-tacrine (IC50, 0.02μM) prevented glutamate-induced excitotoxicity more substantially than memantine (IC50, 0.7μM). In addition, bis(7)-tacrine was more efficient than memantine in buffering the intracellular Ca2+ triggered by glutamate. In cultured rat hippocampal neurons, bis(7)-tacrine inhibited 50μM NMDA-activated current in a concentration-dependent manner with an IC50 of 0.68±0.07μM, which is five times more potent than that produced by memantine (IC50, 3.41±0.36μM; p <0.05). By contrast, bis(7)-tacrine, up to 5μM, did not significantly affect the current activated by 50μM AMPA or 50μM kainate. These results suggest that bis(7)-tacrine is more potent than memantine against glutamate-induced neurotoxicity by selectively inhibiting NMDA-activated current. [Copyright &y& Elsevier]

To explore the association of the phenotype of ATP-activated current with the genotype of P2X1-6 subunits in nociceptors, we developed a method that allows us to label nociceptive neurons innervating tooth-pulp in rat trigeminal ganglion (TG) neurons using a retrograde fluorescence-tracing method, to record ATP-activated current in freshly isolated fluorescence-labeled neurons, and then to conduct single cell immunohistochemical staining for P2X1-6 subunits in the same neuron. We found that fast application of 100 μM ATP to fluorescence-traced TG neurons produced robust inward current in 87% (96/110) of cells tested. The diameter of cells varied from 16 to 56 μm. Three types of ATP-activated current (F, I and S) were recorded with distinct rise times of the current (R 10–90 , P < 0.05). There was a positive correlation between the cell diameter and the value of R 10–90 (P < 0.05): the value of R 10-90 increased with increases in the cell diameter. Cells responsive to ATP with the type F current mainly showed positive staining for P2X3 and P2X5, but negative staining for P2X2; cells responsive to ATP with the type I current showed positive staining for P2X1-3 and P2X5, but negative staining for P2X4; and cells responsive to ATP with the type S current showed positive staining for P2X1-5, but negative staining for P2X6. The present findings suggest that in addition to P2X3 subunits, P2X5 subunits are also involved in the generation of the F type of ATP-activated current in small-sized nociceptive neurons. In addition to the P2X2/3 subunit-containing channels, more complex uncharacterized combinations of P2X1-5 subunits exist in native medium-sized nociceptive neurons exhibiting the I and S types of ATP-activated current. In addition, the P2X6 subunit is not a main subunit involved in the nociceptive signal in rat TG neurons innervating tooth-pulp. [ABSTRACT FROM AUTHOR]

Abstract: Relatively little information is available about the molecular mechanism of ethanol inhibition of P2X receptors. Here, we investigated the possibility that 10 conserved cysteine residues in the extracellular loop of the rat P2X4 receptor may regulate ethanol inhibition of the receptor using a series of individual cysteine to alanine point mutations. Each of the mutated receptors generated robust inward current in response to ATP and the mutations produced less than a sixfold change in the ATP EC50 value. For the C116A, C126A, C149A, and C165A mutants, 100mM ethanol did not significantly affect the current activated by an EC40 concentration of ATP. By contrast, for the C261A and C270A mutants, ethanol inhibited ATP-activated current in a competitive manner similar to that for the wild-type receptor. Interestingly, for the C132A, C159A, C217A, and C227A mutants, ethanol inhibited ATP-activated current, but decreased the maximal response to ATP by 70–75% without significantly changing the EC50 value of ATP, thus exhibiting a noncompetitive-type inhibition. The results suggest that cysteines and disulfide bonds between cysteines are differentially involved in the inhibition of the rat P2X4 receptor by ethanol. [Copyright &y& Elsevier]

Abstract: Bis(7)-tacrine [bis(7)-tetrahydroaminacrine] acts as an AChE inhibitor and also exerts modulatory effects on many ligand-gated ion channels and voltage-gated Ca2+ and K+ channels. It has been reported previously that tacrine and some other AChE inhibitors suppressed I K(A) in central and peripheral neurons. The present study aimed to explore whether bis(7)-tacrine could modulate the function of native delayed rectifier potassium channels in DRG neurons and KV1.2 encoded potassium channels expressed in oocytes. We found that both delayed rectifier potassium currents (I K(DR)) in rat DRG neurons and the currents recorded from oocytes expressing KV1.2 () were suppressed by bis(7)-tacrine, the potency of which was two orders greater than that of tacrine. The IC50 values for bis(7)-tacrine and tacrine inhibition of I K(KD) in DRG neurons were 0.72±0.05 and 58.3±3.7μM, respectively; while the two agents inhibited in oocytes with an IC50 of 0.24±0.06 and 102.1±21.5μM, respectively. The possible mechanism for bis(7)-tacrine inhibition of I K(A) and was identified as the suppression of their activation, inactivation. [Copyright &y& Elsevier]

Accumulating evidence has demonstrated that voltage-gated potassium channels (Kv channels) were associated with regulating cell proliferation and apoptosis in tumor cells. Our previous study proved that the Kv channel blocker 4-aminopyridine (4-AP) could inhibit cell proliferation and induce apoptosis in glioma. However, the precise mechanisms were not clear yet. MicroRNAs (miRNAs) are small noncoding RNAs that act as key mediators in the progression of tumor, so the aim of this study was to investigate the role of miRNAs in the apoptosis-promoting effect of 4-AP in glioma cells. Using a microRNA array, we found that 4-AP altered the miRNA expression in glioma cells, and the down-regulation of miR-10b-5p induced by 4-AP was verified by real-time PCR. Transfection of miR-10b-5p mimic significantly inhibited 4-AP-induced caspases activation and apoptosis. Moreover, we verified that apoptosis-related molecule Apaf-1 was the direct target of miR-10b-5p. Furthermore, miR-10b-5p mimic significantly inhibited 4-AP-induced up-regulation of Apaf-1 and its downstream apoptosis-related proteins, such as cleaved caspase-3. In conclusion, Kv channel blocker 4-AP may exert its anti-tumor effect by down-regulating the expression of miR-10b-5p and then raised expression of Apaf-1 and its downstream apoptosis-related proteins. Current data provide evidence that miRNAs play important roles in Kv channels-mediated cell proliferation and apoptosis.

Accumulating evidence has proved that potassium channels (K+ channels) are involved in regulating cell proliferation, cell cycle progression and apoptosis of tumor cells. However, the precise cellular mechanisms are still unknown. In the present study, we investigated the effect and mechanisms of quinidine, a commonly used voltage-gated K+ channel blocker, on cell proliferation and apoptosis of human glioma U87-MG cells. We found that quinidine significantly inhibited the proliferation of U87-MG cells and induced apoptosis in a dose-dependent manner. The results of caspase colorimetric assay showed that the mitochondrial pathway was the main mode involved in the quinidine-induced apoptotic process. Furthermore, the concentration range of quinidine, which inhibited voltage-gated K+ channel currents in electrophysiological assay, was consistent with that of quinidine inhibiting cell proliferation and inducing cell apoptosis. In U87-MG cells treated with quinidine (100 µmol/l), 11 of 2,042 human microRNAs (miRNAs) were upregulated and 16 were downregulated as detected with the miRNA array analysis. The upregulation of miR-149-3p and downregulation of miR-424-5p by quinidine treatment were further verified by using quantitative real-time PCR. In addition, using miRNA target prediction program, putative target genes related to cell proliferation and apoptosis for two differentially expressed miRNAs were predicted. Taken together, these data suggested that the anti-proliferative and pro-apoptosis effect of voltage-gated K+ channel blocker quinidine in human glioma cells was mediated at least partly through regulating expression of miRNAs, and provided further support for the mechanisms of voltage-gated K+ channels in mediating cell proliferation and apoptosis.

Increasing evidence indicates that potassium (K+) channels play important roles in the growth and development of human cancer. In the present study, we investigated the contribution of and the mechanism by which K+ channels control the proliferation and tumor development of U87-MG human glioma cells. A variety of K+ channel blockers and openers were used to differentiate the critical subtype of K+ channels involved. The in vitro data demonstrated that selective blockers of voltage-gated K+ (K(V)) channels or ATP-sensitive K+ (K(ATP)) channels significantly inhibited the proliferation of U87-MG cells, blocked the cell cycle at the G0/G1 phase and induced apoptosis. In the U87-MG xenograft model in nude mice, K(V) or K(ATP) channel blockers markedly suppressed tumor growth in vivo. Furthermore, electrophysiological results showed that KV or KATP channel blockers inhibited K(V)/K(ATP) channel currents as well as cell proliferation and tumor growth over the same concentration range. In contrast, iberiotoxin, a selective blocker of calcium-activated K+ channels, had no apparent effect on the cell proliferation, cell cycle or apoptosis of U87-MG cells. In addition, the results of fluorescence assays indicated that blockers of K(V) or K(ATP) channels attenuated intracellular Ca2+ signaling by blocking Ca2+ influx in U87-MG cells. Taken together, these data suggest that K(V) and K(ATP) channels play important roles in the proliferation of U87-MG cells and that the influence of K(V) and K(ATP) channels may be mediated by a Ca2+-dependent mechanism.

Relatively little information is available about the molecular mechanism of ethanol inhibition of P2X receptors. Here, we investigated the possibility that 10 conserved cysteine residues in the extracellular loop of the rat P2X4 receptor may regulate ethanol inhibition of the receptor using a series of individual cysteine to alanine point mutations. Each of the mutated receptors generated robust inward current in response to ATP and the mutations produced less than a sixfold change in the ATP EC50 value. For the C116A, C126A, C149A, and C165A mutants, 100 mM ethanol did not significantly affect the current activated by an EC40 concentration of ATP. By contrast, for the C261A and C270A mutants, ethanol inhibited ATP-activated current in a competitive manner similar to that for the wild-type receptor. Interestingly, for the C132A, C159A, C217A, and C227A mutants, ethanol inhibited ATP-activated current, but decreased the maximal response to ATP by 70-75% without significantly changing the EC50 value of ATP, thus exhibiting a noncompetitive-type inhibition. The results suggest that cysteines and disulfide bonds between cysteines are differentially involved in the inhibition of the rat P2X4 receptor by ethanol.

Bis(7)-tacrine [bis(7)-tetrahydroaminacrine] acts as an AChE inhibitor and also exerts modulatory effects on many ligand-gated ion channels and voltage-gated Ca(2+) and K(+) channels. It has been reported previously that tacrine and some other AChE inhibitors suppressed I(K(A)) in central and peripheral neurons. The present study aimed to explore whether bis(7)-tacrine could modulate the function of native delayed rectifier potassium channels in DRG neurons and K(V)1.2 encoded potassium channels expressed in oocytes. We found that both delayed rectifier potassium currents (I(K(DR))) in rat DRG neurons and the currents recorded from oocytes expressing K(V)1.2 (I(K(K(V)1.2))) were suppressed by bis(7)-tacrine, the potency of which was two orders greater than that of tacrine. The IC(50) values for bis(7)-tacrine and tacrine inhibition of I(K(KD)) in DRG neurons were 0.72+/-0.05 and 58.3+/-3.7 microM, respectively; while the two agents inhibited I(K(K(V)1.2)) in oocytes with an IC(50) of 0.24+/-0.06 and 102.1+/-21.5 microM, respectively. The possible mechanism for bis(7)-tacrine inhibition of I(K(A)) and I(K(K(V)1.2)) was identified as the suppression of their activation, inactivation.