Inactivation of calcium-activated chloride channels in smooth muscle by calcium/calmodulin-dependent protein kinase

To determine the mechanisms responsible for the termination of Ca²⁺-activated Cl⁻ currents (I_Cl(Ca)), simultaneous measurements of whole cell currents and intracellular Ca²⁺ concentration ([Ca²⁺]_i) were made in equine tracheal myocytes. In nondialyzed cells, or cells dialyzed with 1 mM ATP, I_Cl(Ca) decayed before the [Ca²⁺]_i decline, whereas the calcium-activated potassium current decayed at the same rate as [Ca²⁺]_i. Substitution of AMP-PNP or ADP for ATP markedly prolonged the decay of I_Cl(Ca), resulting in a rate of current decay similar to that of the fall in [Ca²⁺]_i. In the presence of ATP, dialysis of the calmodulin antagonist W7, the Ca²⁺/calmodulin-dependent kinase II (CaMKII) inhibitor KN93, or a CaMKII-specific peptide inhibitor the rate of I_Cl(Ca) decay was slowed and matched the [Ca²⁺]_i decline, whereas H7, a nonspecific kinase inhibitor with low affinity for CaMKII, was without effect. When a sustained increase in [Ca²⁺]_i was produced in ATP dialyzed cells, the current decayed completely, whereas in cells loaded with 5′-adenylylimidodiphosphate (AMP-PNP), KN93, or the CaMKII inhibitory peptide, I_Cl(Ca) did not decay. Slowly decaying currents were repeatedly evoked in ADP- or AMP-PNP-loaded cells, but dialysis of adenosine 5′-O-(3-thiotriphosphate) or okadaic acid resulted in a smaller initial I_Cl(Ca), and little or no current (despite a normal [Ca²⁺]_i transient) with a second stimulation. These data indicate that CaMKII phosphorylation results in the inactivation of calcium-activated chloride channels, and that transition from the inactivated state to the closed state requires protein dephosphorylation.     

Relevance of the reaction of a manganese(III) chelate with hydroxide ion to photosynthesis: Reaction of hydroxide ion with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) in ligating and nonligating solvents

The reaction of HO^- with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) chloride [(TMP)Mn^III(Cl)] in ligating solvents (CH₃CN, dimethyl sulfoxide, pyridine) results in formation of (TMP)Mn^II (≈10⁶ M^-1·s^-r), which in a slower reaction is converted to a product whose structure is suggested to be that of a porphyrin manganese(III) peroxo dimer. Admittance of O₂ at any time during these reactions leads to formation of the manganese(III) peroxide (TMP)Mn^III(O₂)^-. In nonligating solvents [CH₂Cl₂, (CH₃)₂CO], the reaction of HO^- with (TMP)Mn^III(Cl) yields (TMP)Mn^IV(OH)₂.     

EDTA-Reduction of Water to Molecular Hydrogen Catalyzed by Visible-Light-Response TiO2-Based Materials Sensitized by Dawson- and Keggin-Type Rhenium(V)-Containing Polyoxotungstates

The synthesis and characterization of a Keggin-type mono-rhenium(V)- substituted polyoxotungstate are described. The dimethylammonium salt [Me₂NH₂]₄[PW₁₁Re^VO₄₀] was obtained as analytically pure homogeneous black-purple crystals by reacting mono-lacunary Keggin polyoxotungstate with [Re^IVCl₆]^2- in water, followed by crystallization from acetone at ca. 5 °C. Single-crystal X-ray structural analysis of [PW₁₁Re^VO₄₀]^4- revealed a monomeric structure with overall T_d symmetry. Characterization of [Me₂NH₂]₄[PW₁₁Re^VO₄₀] was also accomplished by elemental analysis, magnetic susceptibility, TG/DTA, FTIR, UV-vis, diffuse reflectance (DR) UV-vis, and solution ³¹P-NMR spectroscopy. Furthermore, [PW₁₁Re^VO₄₀]^4- and the Dawson-type dirhenium(V)-oxido-bridged polyoxotungstate [O{Re^V(OH)(α₂-P₂W₁₇O₆₁)}₂]^14- were supported onto anatase TiO₂ surface by the precipitation methods using CsCl and Pt(NH₃)₄Cl₂. With these materials, hydrogen evolution from water in the presence of EDTA·2Na (ethylenediamine tetraacetic acid disodium salt) under visible light irradiation (≥400 nm) was achieved.     

Effects of ethanol on sodium, 3-O-methyl glucose,andl-alanine transport in the jejunum

Effects of ethanol on Na⁺, Cl^–, 3-O-methyl glucose (3-O-MG), andl-alanine fluxes were studied in the isolated rabbit jejunal mucosa. Ethanol (3% v/v present on both sides of the mucosa) decreased electrical potential difference (PD), short-circuit current (I_sc) and inhibited active transport of Na⁺, 3-O-MG, andl-alanine. This concentration also increased the permeability of the mucosa for Cl^–, 3-O-MG, andl-alanine. Ethanol at 5.4% potentiated the effects on PD, I_sc, and the permeability for electrolytes and organic substances. These effects of ethanol could not be fully explained by an osmotic action.This research was supported by funds from NIAAA grant 2R01 AA-00194-05.     

Generation of "bastard" molecular ions from van der Waals clusters: Ar(n)(C(2)Cl(4))(m) ions, suspected interlopers in collection of solar neutrinos

Gaseous molecular ions containing argon and perchlorethylene, Ar_n(C₂Cl₄)_m⁺ in which n ≥ 1-29 and m ≥ 1-4, are produced by electron bombardment of van der Waals clusters formed by expanding an Ar/C₂Cl₄ mixture through a supersonic nozzle. Previous attempts to observe such ions in a high-pressure mass spectrometer were not successful, as with many other (“bastard”) ions that similarly lack a stable chemically bound neutral parent molecule. This is probably due to dissociation induced by the large exoergicity from charge transfer between species that differ greatly in ionization potential. Use of van der Waals clusters as parent species avoids entirely the exoergicity problem and thus offers a general method to generate bastard ions. The Ar(C₂Cl₄)_m⁺ ions have been suspected of interfering with collection of ³⁷Ar⁺ ions produced by the ³⁷Cl(v,e^-)³⁷Ar⁺ reaction in the solar neutrino observatory. Although, as shown by our results, these ions are stable, they are unlikely to inhibit collection on the long time scale of the solar neutrino experiment.     

A two-metal ion mechanism operates in the hammerhead ribozyme-mediated cleavage of an RNA substrate

Evidence for a two-metal ion mechanism for cleavage of the HH16 hammerhead ribozyme is provided by monitoring the rate of cleavage of the RNA substrate as a function of La³⁺ concentration in the presence of a constant concentration of Mg²⁺. We show that a bell-shaped curve of cleavage activation is obtained as La³⁺ is added in micromolar concentrations in the presence of 8 mM Mg²⁺, with a maximal rate of cleavage being attained in the presence of 3 μM La³⁺. These results show that two-metal ion binding sites on the ribozyme regulate the rate of the cleavage reaction and, on the basis of earlier estimates of the K_d values for Mg²⁺ of 3.5 mM and >50 mM, that these sites bind La³⁺ with estimated K_d values of 0.9 and >37.5 μM, respectively. Furthermore, given the very different effects of these metal ions at the two binding sites, with displacement of Mg²⁺ by La³⁺ at the stronger (relative to Mg²⁺) binding site activating catalysis and displacement of Mg²⁺ by La³⁺ at the weaker (relative to Mg²⁺) (relative to Mg²⁺) binding site inhibiting catalysis, we show that the metal ions at these two sites play very different roles. We argue that the metal ion at binding site 1 coordinates the attacking 2′-oxygen species in the reaction and lowers the pK_a of the attached proton, thereby increasing the concentration of the attacking alkoxide nucleophile in an equilibrium process. In contrast, the role of the metal ion at binding site 2 is to catalyze the reaction by absorbing the negative charge that accumulates at the leaving 5′-oxygen in the transition state. We suggest structural reasons why the Mg²⁺–La³⁺ ion combination is particularly suited to demonstrating these different roles of the two-metal ions in the ribozyme cleavage reaction.     

Electrogenic ion transport in mammalian colon involves an ammonia-sensitive apical membrane K+ conductance

It is remarkable that high ammonia concentrations can be present within the colonic lumen without compromising normal epithelial function. We investigated the impact of luminal ammonia on Cl^– secretion in native tissue. Stripped human colonic mucosa and unstripped rat distal colon were used. Paired samples were mounted in modified Ussing chambers for electrophysiological studies. In rat distal colon, apical ammonia dose-dependently blocked forskolin-activated short-circuit current with an IC₅₀ 5 mM. Basolateral NH₄Cl was less effective. Luminal methylamine (50 mM), chromanol 293 B (10–50 M), and Ba²⁺ (5 mM) blocked cAMP-activated short-circuit current but apical clotrimazole (100 M) was without effect. In stripped human colonic mucosa, luminal but not basolateral NH₄Cl (10 mM) and luminal Ba²⁺ (5 mM) suppressed forskolin-activated short-circuit current. Ammonia may be an endogenous regulator of colonic water and salt secretion. Apical K⁺ channels may be involved in the regulation of cAMP-stimulated Cl^– secretion in mammalian colon.     

Crystal engineering of lattice metrics of perhalometallate salts and MOFs

The synthesis of the salt 3 and metallo-organic framework (MOF) [{(4,4^′-bipy)CoBr₂}_n] 4 by a range of solid state (mechanochemical and thermochemical) and solution methods is reported; they are isostructural with their respective chloride analogues 1 and 2. 3 and 4 can be interconverted by means of HBr elimination and absorption. Single phases of controlled composition and general formula [4,4^′-H₂bipy][CoBr_4-xCl_x] 5_x may be prepared from 2 and 4 by solid—gas reactions involving HBr or HCl respectively. Crystalline single phase samples of 5_x and [{(4,4^′-bipy)CoBr_2-xCl_x}_n] 6_x were prepared by solid-state mechanochemical routes, allowing fine control over the composition and unit cell volume of the product. Collectively these methods enable continuous variation of the unit cell dimensions of the salts [4,4^′-H₂bipy][CoBr_4-xCl_x] (5_x) and the MOFs [{(4,4^′-bipy)CoBr_2-xCl_x}_n] (6_x) by varying the bromide to chloride ratio and establish a means of controlling MOF composition and the lattice metrics, and so the physical and chemical properties that derive from it.     

The effect of bicarbonate on photosynthetic oxygen evolution in flashing light in chloroplast fragments

The ability of bicarbonate ion (HCO₃^-) to stimulate photosynthetic oxygen evolution in maize chloroplast fragments exposed to continuous light depends on light intensity. Stimulation by HCO₃^- is less at low intensities. In HCO₃^--depleted chloroplasts exposed to brief saturating light flashes, period 4 oscillations (in O₂ yield per flash) are damped within three cycles. Readdition of HCO₃^- to these preparations restores the oscillatory pattern to higher flash numbers, indicating that HCO₃^- reduces the probability of “misses” in the photosystem II reaction center. The rate of the dark relaxation reaction S_n^′ → S_n+1 (where S refers to the oxidation state of the oxygen-evolving mechanism and n = 0, 1, or 2), after a photoact in the photosystem II reaction center, is retarded in HCO₃^--depleted chloroplasts compared to the rate for this reaction in depleted chloroplasts to which HCO₃^- has been resupplied. However, the final oxygen-evolving reaction after the accumulation of four positive charges appears to be independent of HCO₃^-. Bicarbonate has no effect on the dark deactivation of the higher oxidation states (S₂ and S₃) of the positive charge-accumulating system. We propose two alternate ways in which the kinetic model of oxygen evolution developed by Kok et al. [(1970) Photochem. Photobiol. 11, 457-475] can be extended to include the action of HCO₃^-.     

Picosecond photochemistry of a cofacial diporphyrin containing iron(III) and zinc(II): Mimicking electron transfer between cytochrome c and the primary electron donor in reaction centers of photosynthetic bacteria

Comparison of picosecond kinetic and spectroscopic data for Zn octaethylporphine and Fe(III)Cl octaethylporphine with that for Zn—Fe(III)Cl, a cofacial diporphyrin composed of a Zn porphyrin covalently bound to an Fe(III)Cl porphyrin with two chains of five atoms each, supports the assignment of a light-driven electron transfer (k > 10¹¹s^-1) within Zn—Fe(III)Cl to form [Zn⁺·—Fe(II)]Cl. The kinetics (k ≈ 10¹⁰s^-1) and thermodynamics of the reverse electron transfer are compared to those of a similar electron transfer in bacterial photosynthesis, the reduction of an oxidized bacteriochlorophyll dimer, (BChl)₂⁺·, by Fe(II) cytochrome c.     

Iron-sulfur clusters II: Kinetics of ligand exchange studied on a water-soluble Fe(4)S(4)(SR)(4) cluster

The water-soluble tetranuclear iron-sulfur cluster ion Fe₄S₄(SCH₂CH₂CO₂^-)₄^6- (II) has been prepared. The stability of II in water is sufficient to allow the spectrotitrimetric determination of the pK_a of its Fe₄S₄ core as 7.4. In our hands the one-electron reductions of compounds I [Fe₄S₄(SR)₄^2-, R = alkyl or aryl,] are thermodynamically irreversible with associated E_1/2 values greater than those for one-electron reduction of ferredoxins. In contrast, the one-electron reduction of II is thermodynamically reversible and the associated potential (-0.58 V versus hydrogen electrode) approaches closely that of the ferredoxins. The kinetics for ligand exchange of II as a function of pH and thiol concentration are in accord with four reversible mercaptan/lyate species exchange reactions followed by product formation via specific acid and base catalysis. Preliminary experiments indicate the nucleophilic order towards II to be Cl^- [unk] Br^- < HO^- < CN^-.     

The Detection of Ionophorous Antibiotic-Cation Complexes in Water with Fluorescent Probes

The binding of alkali cations by the ionophorous antibiotics valinomycin, nigericin, alamethicin, and the macrotetralide actins has been shown to occur, in aqueous media, by the use of the fluorescent probes 1-anilino-8-naphthalene sulfonate and 2-p-toluidinyl-6-naphthalene sulfonate. The interaction of the ionophore-cation complexes with the fluorescent dyes produced enhanced fluorescence emission, increased lifetime and polarization, and a significant blue-shift of the emission maxima of the fluorescence spectrum. At constant antibiotic and fluorophore concentrations in water, the intensity of the fluorescence emission was found to be a function of the cation concentration. This permitted relative cation affinities to be determined for alamethicin (Na⁺ K⁺), valinomycin (Rb⁺ > K⁺ > Cs⁺), nigericin (K⁺ > Rb⁺ > Na⁺ > Cs⁺) and trinactin (NH₄⁺ > K⁺ > Rb⁺ > Cs⁺).     

Mechanism(s) of Chloride Transport in Human Distal Colonic Apical Membrane Vesicles

Previous studies from our laboratory have demonstrated the presence of an electroneutral Cl^–/HCO₃ ^– exchange process across the human proximal colonic apical membrane vesicles (AMV). However, very little is known about the mechanism(s) of chloride transport in the apical membrane of the human distal colon. Utilizing AMV purified from organ donor distal colonic mucosa and a rapid Millipore filtration technique, the mechanisms of ³⁶Cl^– uptake into these vesicles were examined. Outwardly directed OH^– and HCO₃ ^– gradients markedly increased the uptake of ³⁶Cl^– into these vesicles, demonstrating a transient accumulation over the equilibrium uptake. Voltage clamping in the presence of K⁺/valinomycin reduced the OH^– and HCO₃ ^– gradient-stimulated ³⁶Cl^– uptake into these vesicles by 30% indicating that the conductive Cl^– uptake pathway was present in these vesicles along with the electroneutral exchange process. Under voltage-clamped conditions, the inhibitors the bicarbonate transporters, DIDS and SITS (1 mM), inhibited OH^– and HCO₃ ^– gradient-stimulated ³⁶Cl^– uptake by 50%. Acetazolamide showed small but significant inhibition of chloride uptake. Amiloride, bumetanide, and furosemide failed to inhibit ³⁶Cl^– uptake. Chloride uptake into these vesicles exhibited saturation kinetics with an apparent K _m for chloride of 16.7 mM and a V _max of 5.9 nmol/mg/15 sec. Chloride, acetate, nitrate, but not sulfate (50 mM each), inhibited 5 mM ³⁶Cl^– uptake. Inwardly directed gradients of Na⁺, K⁺ or both together did not stimulate chloride uptake into these vesicles indicating that the uptake of Cl^– and Na⁺ in human distal colonic AMV does not involve Na-Cl or Na-K-2Cl cotransport. In conclusion, these studies demonstrate that Cl^– transport across the apical membranes of human distal colon involves both conductive pathway and electroneutral Cl^–/HCO₃ ^– (OH^–) exchange processes. In view of our previous demonstration of a Na⁺/H⁺ exchange process in these AMV, we propose that the operation of dual ion exchange mechanisms of Na⁺/H⁺ and Cl^–/HCO₃ ^– is the primary mode of electroneutral NaCl absorption across the apical membranes of the enterocytes of the human distal colon.     

The Vital Role of La2O3 on the La2O3-CaO-B2O3-SiO2 Glass System for Shielding Some Common Gamma Ray Radioactive Sources

The role La₂O₃ on the radiation shielding properties of La₂O₃-CaO-B₂O₃-SiO₂ glass systems was investigated. The energies were selected between 0.284 and 1.275 MeV and Phy-X software was used for the calculations. BLa10 glass had the least linear attenuation coefficient (LAC) at all the tested energies, while BLa30 had the greatest, which indicated that increasing the content of La₂O₃ in the BLa-X glasses enhances the shielding performance of these glasses. The mass attenuation coefficient (MAC) of BLa15 decreases from 0.150 cm²/g to 0.054 cm²/g at energies of 0.284 MeV and 1.275 MeV, respectively, while the MAC of BLa25 decreases from 0.164 cm²/g to 0.053 cm²/g for the same energies, respectively. At all energies, the effective atomic number (Z_eff) values follow the trend BLa10 < BLa15 < BLa20 < BLa25 < BLa30. The half value thickness (HVL) of the BLa-X glass shields were also investigated. The minimum HVL values are found at 0.284 MeV. The HVL results demonstrated that BLa30 is the most space-efficient shield. The tenth value layer (TVL) results demonstrated that the glasses are more effective attenuators at lower energies, while decreasing in ability at greater energies. These mean free path results proved that increasing the density of the glasses, by increasing the amount of La₂O₃ content, lowers MFP, and increases attenuation, which means that BLa30, the glass with the greatest density, absorbs the most amount of radiation.     

Membrane targeting of cGMP-dependent protein kinase is required for cystic fibrosis transmembrane conductance regulator Cl− channel activation

A recently cloned isoform of cGMP-dependent protein kinase (cGK), designated type II, was implicated as the mediator of cGMP-provoked intestinal Cl⁻ secretion based on its localization in the apical membrane of enterocytes and on its capacity to activate cystic fibrosis transmembrane conductance regulator (CFTR) Cl⁻ channels. In contrast, the soluble type I cGK was unable to activate CFTR in intact cells, although both cGK I and cGK II could phosphorylate CFTR in vitro. To investigate the molecular basis for the cGK II isotype specificity of CFTR channel gating, we expressed cGK II or cGK I mutants possessing different membrane binding properties by using adenoviral vectors in a CFTR-transfected intestinal cell line, and we examined the ability of cGMP to phosphorylate and activate the Cl⁻ channel. Mutation of the cGK II N-terminal myristoylation site (Gly² → Ala) reduced cGK II membrane binding and severely impaired cGK II activation of CFTR. Conversely, a chimeric protein, in which the N-terminal membrane-anchoring domain of cGK II was fused to the N terminus of cGK Iβ, acquired the ability to associate with the membrane and activate the CFTR Cl⁻ channel. The potency order of cGK constructs for activation of CFTR (cGK II > membrane-bound cGK I chimer nonmyristoylated cGK II > cGK Iβ) correlated with the extent of ³²P incorporation into CFTR observed in parallel measurements. These results strongly support the concept that membrane targeting of cGK is a major determinant of CFTR Cl⁻ channel activation in intact cells.     

Structure of a Fe4O6-Heteraadamantane-Type Hexacation Stabilized by Chelating Organophosphine Oxide Ligands

Metal-containing heteraadamantanes are compounds of interest due to their spectroscopic and magnetic properties, which make them promising materials for non-linear optics and semiconductors. Herein we report the comprehensive structural characterization of a new coordination compound of the formula [(µ-OH′)₂(µ-OH″)₄(O = P(Ph₂)CH₂CH₂(Ph₂)P = O)₄{Fe(t-BuOH)}₄](PF₆)₄(Cl)₂ with the chelating ligand Ph₂P(O)-CH₂CH₂-P(O)Ph₂. The compound crystallizes as a polynuclear metal complex with the adamantane-like core [Fe₄O₆] in the space group I-43d of a cubic system. The single-crystal XRD analysis showed that the crystal contains one symmetrically independent octahedrally coordinated Fe atom in the oxidation state +3. The adamantine-like scaffold of the Fe complex is formed by hydroxy bridging oxygen atoms only. Hirshfeld surface analysis of the bridging oxygen atoms revealed two types of µ-OH groups, which differ in the degree of exposure and participation in long-range interactions. Additionally, the Hirshfeld surface analysis supported by the enrichment ratio calculations demonstrated the high propensity of the title complex to form C-H^…Cl, C-H^…F and C-H^…O interactions.     

Synthesis and characterization of a photosensitive interface for hydrogen generation: Chemically modified p-type semiconducting silicon photocathodes

p-Si photocathodes functionalized first with an N,N′-dialkyl-4,4′-bipyridinium redox reagent, (PQ^2+/+-)_surf, and then with a Pt precursor, PtCl₆^2-, give significant efficiency (up to 5%) for photoelectrochemical H₂ generation with 632.8-nm light. Naked p-Si photocathodes give nearly zero efficiency, owing to poor H₂ evolution kinetics that are improved by the (PQ^2+/+-)_surf/Pt modification. The mechanism of H₂ evolution from p-Si/(PQ^2+/+-)_surf/Pt is first photoexcitation of electrons to the conduction band of Si followed by (PQ²⁺)_surf → (PQ^+-)_surf reduction. The dispersion of Pt then catalyzes H₂O reduction to give H₂ and regeneration of (PQ²⁺)_surf. The overall energy conversion efficiency rivals the best direct optical to chemical conversion systems reported to date.     

Multiphysics and Multiscale Modeling of Coupled Transport of Chloride Ions in Concrete

Chloride ions (Cl⁻)-induced corrosion is one of the main degradation mechanisms in reinforced concrete (RC) structures. In most situations, the degradation initiates with the transport of Cl⁻ from the surface of the concrete towards the reinforcing steel. The accumulation of Cl⁻ at the steel-concrete interface could initiate reinforcement corrosion once a threshold Cl⁻ concentration is achieved. An accurate numerical model of the Cl⁻ transport in concrete is required to predict the corrosion initiation in RC structures. However, existing numerical models lack a representation of the heterogenous concrete microstructure resulting from the varying environmental conditions and the indirect effect of time dependent temperature and relative humidity (RH) on the water adsorption and Cl⁻ binding isotherms. In this study, a numerical model is developed to study the coupled transport of Cl⁻ with heat, RH and oxygen (O₂) into the concrete. The modeling of the concrete microstructure is performed using the Virtual Cement and Concrete Testing Laboratory (VCCTL) code developed by the U.S. National Institute of Standards and Technology (NIST). The concept of equivalent maturation time is utilized to eliminate the limitation of simulating concrete microstructure using VCCTL in specific environmental conditions such as adiabatic. Thus, a time-dependent concrete microstructure, which depends on the hydration reactions coupled with the temperature and RH of the environment, is achieved to study the Cl⁻ transport. Additionally, Cl⁻ binding isotherms, which are a function of the pH of the concrete pore solution, Cl⁻ concentration, and weight fraction of mono-sulfate aluminate (AFm) and calcium-silicate-hydrate (C-S-H), obtained from an experimental study by the same authors are utilized to account for the Cl⁻ binding of cement hydration products. The temperature dependent RH diffusion was considered to account for the transport of Cl⁻ with moisture transport. The temperature and RH diffusion in the concrete domain, composite theory, and Cl⁻ binding and water adsorption isotherms are used in combination, to estimate the ensuing Cl⁻ diffusion field within the concrete. The coupled transport process of heat, RH, Cl⁻, and O₂ is implemented in the Multiphysics Object-Oriented Simulation Environment (MOOSE) developed by the U.S. Idaho National Laboratory (INL). The model was verified and validated using data from multiple experimental studies with different concrete mixture proportions, curing durations, and environmental conditions. Additionally, a sensitivity analysis was performed to identify that the water-to-cement (w/c) ratio, the exposure duration, the boundary conditions: temperature, RH, surface Cl⁻ concentration, Cl⁻ diffusion coefficient in the capillary water, and the critical RH are the important parameters that govern the Cl⁻ transport in RC structures. In a case study, the capabilities of the developed numerical model are demonstrated by studying the complex 2D diffusion of Cl⁻ in a RC beam located in two different climatic regions: warm and humid weather in Galveston, Texas, and cold and dry weather in North Minnesota, Minnesota, subjected to time varying temperature, RH, and surface Cl⁻ concentrations.     

Effect of entacapone on colon motility and ion transport in a rat model of Parkinson’s disease

AIM: To study the effects of entacapone, a catecholO-methyltransferase inhibitor, on colon motility and electrolyte transport in Parkinson’s disease(PD) rats.METHODS: Distribution and expression of catecholO-methyltransferase(COMT) were measured by immunohistochemistry and Western blotting methods. The colonic smooth muscle motility was examined in vitroby means of a muscle motility recording device. The mucosal electrolyte transport of PD rats was examined by using a short-circuit current(I SC) technique and scanning ion-selective electrode technique(SIET). Intracellular detection of c AMP and c GMP was accomplished by radioimmunoassay testing. RESULTS: COMT was expressed in the colons of both normal and PD rats, mainly on the apical membranes of villi and crypts in the colon. Compared to normal controls, PD rats expressed less COMT. The COMT inhibitor entacapone inhibited contraction of the PD rat longitudinal muscle in a dose-dependent manner. The β2 adrenoceptor antagonist ICI-118,551 blocked this inhibitory effect by approximately 67%(P < 0.01). Entacapone increased mucosal ISC in the colon of rats with PD. This induction was significantly inhibited by apical application of Cl- channel blocker diphenylamine-2, 2’-dicarboxylic acid, basolateral application of Na+-K+-2Cl-co-transporter antagonist bumetanide, elimination of Cl- from the extracellular fluid, as well as pretreatment using adenylate cyclase inhibitor MDL12330 A. As an inhibitor of prostaglandin synthetase, indomethacin can inhibit entacaponeinduced ISC by 45%(P < 0.01). When SIET was applied to measure Cl- flux changes, this provided similar results. Entacapone significantly increased intracellular c AMP content in the colonic mucosa, which was greatly inhibited by indomethacin.CONCLUSION: COMT expression exists in rat colons. The β2 adrenoceptor is involved in the entacaponeinduced inhibition of colon motility. Entacapone induces c AMP-dependent Cl- secretion in the PD rat.     

Nonenzymatic and enzymatic hydrolysis of alkyl halides: A theoretical study of the SN2 reactions of acetate and hydroxide ions with alkyl chlorides

The S_N2 displacements of chloride ion from CH₃Cl, C₂H₅Cl, and C₂H₄Cl₂ by acetate and hydroxide ions have been investigated, using ab initio molecular orbital theory at the HF/6–31+G(d), MP2/6–31+G(d), and MP4/6–31+G(d) levels of theory. The central barriers (calculated from the initial ion–molecule complex) of the reactions, the differences of the overall reaction energies, and the geometries of the transition states are compared. Essential stereochemical changes before and after the displacement reactions are described for selected cases. The gas phase reactions of hydroxide with CH₃Cl, C₂H₅Cl, and C₂H₄Cl₂ have no overall barrier, but there is a small overall barrier for the reactions of acetate with CH₃Cl, C₂H₅Cl, and C₂H₄Cl₂. A self-consistent reaction field solvation model was used to examine the S_N2 reactions between methyl chloride and hydroxide ion and between 1,2-dichloroethane and acetate in solution. As expected, the reactions in polar solvent have a large barrier. However, the transition state structures determined by ab initio calculations change only slightly in the presence of a highly polar solvent as compared with the gas phase. We also calibrated the PM3 method for future study of an enzymatic S_N2 displacement of halogen.