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At least 379 records · Page 21Linked to original sources
PubMed2003

The large conductance Ca2+-activated potassium channel (pSlo) of the cockroach Periplaneta americana: structure, localization in neurons and electrophysiology.

Voltage-activated, Ca2+-sensitive K+ channels (BK or maxi K,Ca channels) play a major role in the control of neuronal excitability. We have cloned pSlo, the BK channel alpha subunit of the cockroach Periplaneta americana. The amino acid sequence of pSlo shows 88% identity to dSlo from Drosophila. There are five alternatively spliced positions in pSlo showing differential expression in various tissues. A pSlo-specific antibody prominently stained the octopaminergic dorsal unpaired median (DUM) neurons and peptidergic midline neurons in Periplaneta abdominal ganglia. HEK293 cells expressing pSlo exhibit K+ channels of 170 pS conductance. They have a tendency for brief closures, exhibit subconductance states and show slight inward rectification. Activation kinetics and voltage dependence are controlled by cytoplasmic [Ca2+]. In contrast to dSlo, pSlo channels are sensitive to charybdotoxin and iberiotoxin. Mutagenesis at two positions (E254 and Q285) changed blocking efficacy of charybdotoxin. In contrast to pSlo expressed in HEK293 cells, native IbTx-sensitive K,Ca currents in DUM and in peptidergic neurons, exhibited rapid, partial inactivation. The fast component of the K,Ca current partly accounts for the repolarization and the early after-hyperpolarization of the action potential. By means of Ca2+-induced repolarization, BK channels may reduce the risk of Ca2+ overload in cockroach neurons. Interestingly, the neurons expressing pSlo were also found to express taurine, a messenger that is likely to limit overexcitation by an autocrine mechanism in mammalian central neurons.

Alternative Splicing↗
PubMed1998

Analysis of local structure in the D2/S1-S2 region of the rat skeletal muscle type 1 sodium channel using insertional mutagenesis.

A reporter epitope was inserted at 11 positions in a region encompassing proposed transmembrane segments S1 and S2 in the second repeat domain (D2) of the rat skeletal muscle type 1 sodium channel. All mutations produced full-length membrane-associated protein following transfection into cultured cells, although the level of expression varied with insertion position. Characterization of cognate cRNAs for each mutation in Xenopus oocytes by two-electrode voltage clamp defined a permissive region between the proposed transmembrane regions in which these large insertions did not interfere with channel function. Two of the mutations, in which the point of insertion was within the proposed S1-S2 loop, demonstrated extracellular membrane labeling when studied either by antibody binding in oocytes or by confocal analysis following transfection into primary muscle cells. Our results define the likely boundaries of an extramembrane region linking the S1 and S2 transmembrane segments in D2 and confirm the extracellular location of this S1-S2 loop predicted by current models of channel tertiary structure.

Amino Acid Sequence↗
PubMed1991

Local structure of turbulence in flows with large Reynolds numbers.

Results are reported on an experimental investigation of the characteristics of fine-scale pulsations of the velocity in several shear flows (mixing layer, boundary layer, planar, axially symmetric, and spatial wakes, and in the return channel of a large wind tunnel) in an interval of definite Reynolds numbers R(lambda) [approximately-equal-to] 70-3000 with respect to the Taylor microscale lambda. The characteristic scales of most of the studied flows are quite large, and the integral scale of the turbulence reaches 5 m. The apparatus had a high resolving power-the ratio of the hot-wire length to the Kolmogorov scale was varied in the range 0.8-2.5. It is shown that the Kolmogorov constant C in the "two thirds" law and the constants C(epsilon) and &mgr; in the energy-dissipation correlation function are not universal and have a systematic dependence on the coefficient of external intermittency. The same constants determined in a completely turbulent fluid are universal within the errors of the measurements.

Journal Article↗
PubMed2004

Theoretical study of the local structure and Raman spectra of CaO-SiO2 binary melts.

A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson's GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-O(nb) bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800-1200 cm(-1)) and the symmetrical bending of Si-O(b)-Si, to which the stretching of Si-O(b) bond exhibits the main contribution, is the dominance in the medium-frequency range (400-700 cm(-1)). As the first theoretical results, the Raman scattering coefficient of each Q(i) was found little change along with the variation of composition and temperature.

Journal Article↗
PubMed2005

Phase behavior and local structure of a binary mixture in pores: mean-field lattice model calculations for analyzing neutron scattering data.

We investigate the phase behavior of an asymmetric binary liquid A-W mixture confined between two planar homogenous substrates (slit pore). Molecules of species W interact preferentially with the solid walls via a long-range potential. Assuming nearest-neighbor attractions between the liquid molecules, we employ a lattice-gas model and a mean-field approximation for the grand potential. Minimization of this potential yields the density profiles of thermodynamically stable phases for fixed temperature, chemical potentials of both species, pore width and strengths of attraction. This model is used to analyze experimental small-angle neutron-scattering (SANS) data on the microscopic structure of the binary system isobutyric acid (iBA)+heavy water (D2O) inside a mesoscopic porous matrix (controlled-pore glass of about 10 nm mean pore width). Confinement-independent model parameters are adjusted so that the theoretical liquid-liquid coexistence curve in the bulk matches its experimental counterpart. By choosing appropriate values of the pore width and the attraction strength between substrates and water we analyze the effect of confinement on the phase diagram. In addition to a depression of the liquid-liquid critical point we observe surface induced phase transitions as well as water-film adsorption near the walls. The temperature dependence of the structure of water-rich and iBA-rich phases of constant composition are discussed in detail. The theoretical predictions are consistent with results of the SANS study and assist their interpretation.

Journal Article↗
PubMed2005

Local structure of a phase-separating binary mixture in a mesoporous glass matrix studied by small-angle neutron scattering.

The mesoscopic structure of the binary system isobutyric acid + heavy water (D(2)O) confined in a porous glass (controlled-pore silica glass, mean pore width ca. 10 nm) was studied by small-angle neutron scattering at off-critical compositions in a temperature range above and below the upper critical solution point. The scattering data were analyzed in terms of a structure factor model similar to that proposed by Formisano and Teixeira [Eur. Phys. J. E 1, 1 (2000)], but allowing for both Ornstein-Zernike-type composition fluctuations and domainlike structures in the microphase-separated state of the pore liquid. The results indicate that the phase separation in the pores is shifted by ca. 10 K and spread out in temperature. Microphase separation is pictured as a transition from partial segregation at high temperature, due to the strong preferential adsorption of water at the pore wall, to a tube or capsule configuration of the two phases at low temperatures, depending on the overall composition of the pore liquid. Results for samples in which the composition of the pore liquid can vary with temperature due to equilibration with extra-pore liquid are consistent with this picture.

Journal Article↗
PubMed2006

Pressure dependence of local structure in liquid carbon disulfide.

High pressure x-ray diffraction measurements on liquid carbon disulfide up to 1.2 GPa are performed by using an energy dispersion method. The results are compared with a molecular dynamics calculation with usual Lennard-Jones potential. They give very good agreement for all pressures measured. It becomes clear that the liquid structure changes like hard core liquid up to the pressure just below crystallizing point. The relation between structural change and optical response at high pressure is discussed.

Journal Article↗
PubMed1979

Ribosome structure: localization of 3' end of RNA in small subunit by immunoelectronmicroscopy.

The 3' end of the RNA in the 30S ribosomal subunit of Escherichia coli has been modified by oxidation with sodium periodate and conjugation with the (mono) dinitrophenyl derivative of ethylenediamine. Antibodies, induced with dinitrophenyl-bovine serum albumin, interact with the modified ribosomal subunits. Electron micrographs of negatively stained antibody-subunit complexes show individual ribosomal subunits to which a single antibody molecule is bound and subunit dimers cross-linked by an IgG molecule. The modified 3' terminus has been localized to a single site on the upper portion of the platform region of the 30S subunit. This location is consistent with earlier placements of proteins that react with the 3' end of the RNA.

Dinitrobenzenes↗
PubMed1999

Global and local structural properties of the principal neutralizing determinant of the HIV-1 envelope protein gp120.

The model of spatial structure for the principal neutralizing determinant (PND) of the HIV-1 envelope protein gp120 is proposed in terms of two-dimensional nuclear Overhauser effect (NOE) spectroscopy data. To build the model, the NMR-based theoretical conformational analysis of synthetic PND peptides of length 40, 24, and 12 residues is carried out. The modeling of the molecular spatial structures is performed by a new approach to research of conformationally mobile peptides using the algorithms of the restrained molecular mechanics method developed earlier. The following major conclusions are made based on the analysis of the simulated peptide conformations: i) there is not unique PND structure in solution, ii) there are seven different PND structures each of which agrees with the experimental data and stereochemical criteria used in computing its spatial model, iii) the PND is characterized by irregular conformation containing a number of reverse turns, iv) all of the selected conformations are conserved in the Gly-Pro-Gly-Arg-Ala-Phe stretch, the most probable viral immunodominant epitope. These data allow to suppose that binding properties of this site are determined by the structural motif which forms the conformation of a double beta-turn and appears common for all hexapeptide structures.

HIV Envelope Protein gp120↗
PubMed1963

The fine structural localization of adenosine triphosphatase in the small intestine, kidney, and liver of the rat.

The distribution of the reaction product of a staining method for adenosine triphosphatase (ATPase) in rat small intestine, kidney, and liver was studied with electron microscopy. Several procedures were tried but the best results were obtained from tissue that had been quenched in liquid nitrogen, sectioned at 25 micro in a cryostat, fixed for 30 to 90 minutes at 4 degrees C in formalin-sucrose buffered to pH 7.2, incubated with substrate, and then osmicated and prepared for electron microscopy in the usual way. This procedure enabled the localization of mitochondrial ATPase to be studied. In tissue fixed in small blocks in osmium tetroxide for 3 minutes prior to incubation with substrate, good preservation was noted, and the reaction product for ATPase was localized on the cell membrane and nuclei. The reaction product was present in abundant amount in the nuclei, and particularly within nucleoli, of all tissues studied. Because the histochemical localization of nuclear enzymes poses numerous interpretative problems at the present time, the significance of this nuclear localization is uncertain. Cell (plasma) membranes were the site of localization, especially at areas where it has been proposed that active transport mechanisms may occur, namely, on the microvilli of intestinal epithelium, endothelial lining of capillaries, glomerular epithelial cell membranes, basal infoldings of the cell membrane of renal tubules, on the microvilli of bile canaliculi, and on the microvilli of proximal convoluted tubular epithelial cells. ATPase localization on the cristae mitochondriales was also demonstrated.

Adenosine Triphosphatases↗
PubMed1966

Fine structural localization of acetylcholinesterase in electroplaque of the electric eel.

The electroplaques composing the electric organ of the eel, Electrophorus electricus, have been utilized for the dual purpose of demonstrating the subcellular sites of acetylcholinesterase activity and as a model for comparison of the several cytochemical methods available. Fresh tissue and tissue fixed by immersion in formalin, hydroxyadipaldehyde, or glutaraldehyde was reacted with the Cu-thiocholine method, the Cu-ferrocyanide thiocholine method, or the thiolacetic acid (TAA) method using Pb, Ag, or Au as capture reagents. Controls were obtained by omission of substrate, or by addition to complete media of varying concentrations of different cholinesterase inhibitors. Reactions were run at 0-5 degrees C at a pH range of 5.0-7.1 for 0.25 to 120 min. Regardless of the capture metal, the localization obtained with TAA as substrate was identical with that observed with acetylthiocholine, the majority of precipitate being deposited on or near the external innervated surface of the plaque and within the tubulovesicular organelles opening onto the innervated surface. Both of the thiocholine methods and the Pb-TAA method showed reaction product in synaptic vesicles of the nerve endings innervating the plaque which was uninhibitable by 10(-4)M physostigmine. All methods also showed some inhibitor-sensitive deposition of reaction product in the mucoid material forming the immediate extracellular environment of the innervated surface.

Acetylcholinesterase↗
PubMed1969

A cholinergic component in the innervation of the longitudinal smooth muscle of the guinea pig vas deferens. The fine structural localization of acetylcholinesterase.

Acetylcholinesterase (AChE) has been detected on the plasma membrane of about 25% of the axons in the longitudinal smooth muscle tissue of guinea pig vas deferens. These axons are presumably cholinergic. No enzyme was detected in the remaining 75% of axons. These axons are presumably adrenergic. The plasma membrane of the Schwann cells associated with the cholinergic axons also stained for AChE. Some axon bundles contained only cholinergic or adrenergic axons while others contained both types of axon. When a cholinergic axon approached within 1100 A of a smooth muscle cell, there was a patch of AChE activity on the muscle membrane adjacent to the axon. It is suggested that these approaches are the points of effective transmission from cholinergic axons to smooth muscle cells. Butyrylcholinesterase activity was detected on the plasma membranes of all axons and smooth muscle cells in this tissue.

Acetylcholinesterase↗
PubMed1970

The fine structural localization of endogenous and exogenous peroxidase activity in Kupffer cells of rat liver.

Endogenous peroxidase activity has been demonstrated in sections of rat liver fixed briefly by glutaraldehyde perfusion and incubated in Graham and Karnovsky's medium for cytochemical demonstration of peroxidase activity (29). In 25-40% of sinusoidal cells, an electron-opaque reaction product is localized in segments of the endoplasmic reticulum, including the perinuclear cisternae, a few Golgi vesicles and saccules and in some large membrane-bounded granules. This staining is abolished after prolonged fixation or boiling of tissue sections in glutaraldehyde, and in the absence of H(2)O(2) or DAB from the incubation medium. Furthermore, the reaction is inhibited completely by sodium azide and high concentrations of H(2)O(2), and partially by KCN and aminotriazole. Among the different cells in hepatic sinusoids, the nonphagocytic "fat-storing" cells (39) are always peroxidase negative, whereas the lining cells in process of erythrophagocytosis are consistently peroxidase positive. The possible biological significance of endogenous peroxidase in Kupffer cells is discussed. In addition, the uptake of exogenous horseradish peroxidase by Kupffer cells has been investigated. The exogenous tracer protein, which in contrast to endogenous peroxidase of Kupffer cells is not inhibited by prolonged aldehyde fixation, is taken up by micropinocytosis and remains confined to the lysosomal system of Kupffer cells. The significance of these observations in respect to some recent studies suggesting localization of exogenous peroxidases in the endoplasmic reticulum of Kupffer cells and peritoneal macrophages (22, 23) is briefly discussed.

Aldehydes↗