Showing papers by "Kazan Federal University published in 2000"

Rapid relief of block by mecamylamine of neuronal nicotinic acetylcholine receptors of rat chromaffin cells in vitro: an electrophysiological and modeling study.

Abstract: The mechanism responsible for the blocking action of mecamylamine on neuronal nicotinic acetylcholine receptors (nAChRs) was studied on rat isolated chromaffin cells recorded under whole-cell patch clamp. Mecamylamine strongly depressed (IC(50) = 0.34 microM) inward currents elicited by short pulses of nicotine, an effect slowly reversible on wash. The mecamylamine block was voltage-dependent and promptly relieved by a protocol combining membrane depolarization with a nicotine pulse. Either depolarization or nicotine pulses were insufficient per se to elicit block relief. Block relief was transient; response depression returned in a use-dependent manner. Exposure to mecamylamine failed to block nAChRs if they were not activated by nicotine or if they were activated at positive membrane potentials. These data suggest that mecamylamine could not interact with receptors either at rest or at depolarized level. Other nicotinic antagonists like dihydro-beta-erythroidine or tubocurarine did not share this action of mecamylamine although proadifen partly mimicked it. Mecamylamine is suggested to penetrate and block open nAChRs that would subsequently close and trap this antagonist. Computer modeling indicated that the mechanism of mecamylamine blocking action could be described by assuming that 1) mecamylamine-blocked receptors possessed a much slower, voltage-dependent isomerization rate, 2) the rate constant for mecamylamine unbinding was large and poorly voltage dependent. Hence, channel reopening plus depolarization allowed mecamylamine escape and block relief. In the presence of mecamylamine, therefore, nAChRs acquire the new property of operating as coincidence detectors for concomitant changes in membrane potential and receptor occupancy.

On the Lower Bounds for One-Way Quantum Automata

Abstract: In the paper we consider measured-once (MO-QFA) one-way quantum finite automaton. We prove that for MO-QFA Q that (1=2+Ɛ)-accepts (Ɛ ∈ (0, 1=2)) regular language L it holds that dim(Q) = Ω (log dim(A)/log log dim(A)). In the case Ɛ ∈ (3/8,1/2) we have more precise lower bound dim(Q) = Ω(log dim(A)) where A is a minimal deterministic finite automaton accepting L, dim(Q), and dim(A) are complexity (number of states) of automata Q and A respectively, (1=2-Ɛ) is the error of Q. The example of language presented in [2] show that our lower bounds are tight enough.

EPR and optical spectra of Yb 3+ in CsCdBr 3 : Charge-transfer effects on the energy-level structure of Yb 3+ in the symmetrical pair centers

Abstract: Electron paramagnetic resonance (EPR), optical absorption, fluorescence, and excitation spectra of ${\mathrm{CsCdBr}}_{3}:1%$ ${\mathrm{Yb}}^{3+}$ single crystals were taken at 4.2 K. An analysis of the dependence of the EPR spectrum on the magnetic-field direction and a comparison of the recorded signal shapes with simulated envelopes over the magnetic dipole transitions of the expected dimers containing all ytterbium isotopes were performed. This allowed us to assign the measured EPR spectra unambiguously to the symmetrical pair center of the type ${\mathrm{Yb}}^{3+}{\ensuremath{-}\mathrm{C}\mathrm{d}}^{2+}$ vacancy-${\mathrm{Yb}}^{3+}$ substituting for three adjacent ${\mathrm{Cd}}^{2+}$ ions in the bromine octahedra chains. A distance of 0.596 nm between the magnetically equivalent ${\mathrm{Yb}}^{3+}$ ions was determined from the line splitting due to magnetic dipole-dipole interaction. An interpretation of the optical spectra in compounds containing $({\mathrm{YbBr}}_{6}{)}^{3\mathrm{\ensuremath{-}}}$ complexes is presented, which is based on a crystal-field theory accounting for an interaction between the ground ${4f}^{13}({\mathrm{Yb}}^{3+})[{4p}^{6}({\mathrm{Br}}^{\mathrm{\ensuremath{-}}}){]}_{6}$ and excited ${4f}^{14}({\mathrm{Yb}}^{2+}{)4p}^{5}(\mathrm{Br})[{4p}^{6}({\mathrm{Br}}^{\mathrm{\ensuremath{-}}}){]}_{5}$ charge-transfer configurations. The observed large splitting of the excited ${}^{2}{F}_{5/2}{(4f}^{13})$ crystal-field multiplet is explained on the basis of a quasiresonant hybridization of the $4f$-hole state with the spin orbitals of the charge-transfer states. With physically reasonable values of the fitted model parameters, the calculated energy level diagram of the ${4f}^{13}$ configuration and the g tensor of the ${\mathrm{Yb}}^{3+}$ ion in the crystal-field ground state are in good agreement with the experimental data.

Comparison of mesospheric and lower thermospheric residual wind with High Resolution Doppler Imager, medium frequency, and meteor radar winds

Abstract: The objective of this study is to compare observed mean meridional winds with those deduced from theory. The diabatic circulation is computed from High Resolution Dopper Imager (HRDI) mesospheric and lower thermospheric temperatures during January and July conditions. The meridional wind component is compared with HRDI Eulerian mean meridional winds near 95 km and with seasonal averages of meridional winds at a number of radar medium-frequency (MF) and meteor wind (MW) sites. The diabatic wind is directed from the summer toward the winter hemisphere. Peak values exceed 20 m s−1 and are observed at 105 km near 20° in the summer hemisphere. A secondary maximum of about 10 m s−1 is observed in the wintertime lower mesosphere during the July case. The diabatic wind is qualitatively consistent with HRDI 95-km mean meridional winds at latitudes equatorward of 50°. Time-averaged summertime radar winds are consistent with HRDI and diabatic winds between 50°S and 20°N. At winter midlatitudes, MF radar winds are directed oppositely to the diabatic wind, while one available MW measurement is directed with the diabatic wind. The zonal acceleration implied by the diabatic wind is about 150–200 m s−1 d−1 in the midlatitude summer lower thermosphere.

Factors influencing the cellular location of proteolytic enzymes of Bacillus intermedius

Abstract: Thiol-dependent serine proteinase and glutamylendopeptidase of Bacillus intermedius 3-19 being prevailing enzymes in the total pool of extracellular proteinases (95%) of this microorganism in catalytic active form were detected on the membrane of the cells. Production of these enzymes was maximum on the medium containing inorganic phosphate and gelatin and decreased 2-4-fold on the medium with glucose and lactate. The level of the activity of extracellular enzymes correlated with that of corresponding membrane-bound proteins. The addition of CoCl2 (2 mM) into the medium caused essential increase in extracellular glutamylendopeptidase activity and promoted the release of membrane-bound enzyme into cultural fluid. Proteolytic activity was detected in cytoplasm also. Proteinases localized in cytoplasm were shown to differ in properties from those secreted.

Magnitude of spin and charge density wave amplitudes in underdoped cuprates

Abstract: Self-consistent calculation of spin (charge) density wave (S(C)DW) order parameters have been performed for bilayered cuprates on the basis of a singlet-correlated band model. Evolution of the Fermi surface in the strongly underdoped regime is described by a two-band approach. The smooth development of the pseudogap formation temperature from underdoped to overdoped states is explained and the Fourier amplitudes 〈sq〉 (spin) and 〈eq〉 (charge) modulations are calculated. We have found a maximum of the incommensurability for doping 0.09 ÷ 0.11 holes per copper site.

Effect of nutrients on the accumulation of glutamyl endopeptidase in the culture liquid of Bacillus intermedius 3-19

Abstract: The effect of nutrients and growth conditions on the accumulation of glutamyl endopeptidase in the culture liquid ofBacillus intermedius 3–19 was studied. Glucose and other readily metabolizable carbon sources were found to suppress the production of the enzyme, whereas inorganic phosphate and ammonium cations enhanced it. Protein substrates, such as casein, gelatin, and hemoglobin, did not affect enzyme production. Some bivalent cations (Ca2+, Mg2+, Co2+) increased the production of glutamyl endopeptidase, but others (Zn2+, Fe2+, Cu2+) acted in the opposite way. The rate of enzyme accumulation in the culture liquid increased as the growth rate of the bacterium decreased, so that the maximum enzyme activity was observed in the stationary growth phase. Based on the results of this investigation, an optimal medium for the maximum production of glutamyl endopeptidase byB. intermedius 3–19 was elaborated.