Surface Characteristics and Microbiological Analysis of a Vat-Photopolymerization Additive-Manufacturing Dental Resin

The wide application of additive manufacturing in dentistry implies the further investigation into oral micro-organism adhesion and biofilm formation on vat-photopolymerization (VP) dental resins. The surface characteristics and microbiological analysis of a VP dental resin, printed at resolutions of 50 μm (EG-50) and 100 μm (EG-100), were evaluated against an auto-polymerizing acrylic resin (CG). Samples were evaluated using a scanning electron microscope, a scanning white-light interferometer, and analyzed for Candida albicans (CA) and Streptococcus mutans (SM) biofilm, as well as antifungal and antimicrobial activity. EG-50 and EG-100 exhibited more irregular surfaces and statistically higher mean (Ra) and root-mean-square (rms) roughness (EG-50-Ra: 2.96 ± 0.32 µm; rms: 4.05 ± 0.43 µm/EG-100-Ra: 3.76 ± 0.58 µm; rms: 4.79 ± 0.74 µm) compared to the CG (Ra: 0.52 ± 0.36 µm; rms: 0.84 ± 0.54 µm) (p < 0.05). The biomass and extracellular matrix production by CA and SM and the metabolic activity of SM were significantly decreased in EG-50 and EG-100 compared to CG (p < 0.05). CA and SM growth was inhibited by the pure unpolymerized VP resin (48 h). EG-50 and EG-100 recorded a greater irregularity, higher surface roughness, and decreased CA and SM biofilm formation over the CG.     

Ductile-to-Brittle Transition and Brittle Fracture Stress of Ultrafine-Grained Low-Carbon Steel

Ductile-to-brittle transition (DBT) temperature and brittle fracture stress, σ_F, are important toughness criteria for structural materials. In this paper, low-carbon steels with an ultrafine elongated grain (UFEG) structure (transverse grain size 1.2 μm) and with two ferrite (α)-pearlite structure with grain sizes 10 µm and 18 µm were prepared. The UFEG steel was fabricated using multipass warm biaxial rolling. The tensile tests with a cylindrical specimen and three-point bending tests with a single-edge-notched specimen were performed at −196 °C. The local stress near the notch was quantitatively calculated via finite element analysis (FEA). The σ_F for each sample was quantified based on the experimental results and FEA. The relationship between σ_F and d_α in the wide range of 1.0 μm to 138 μm was plotted, including data from past literature. Finally, the conditions of grain size and temperature that cause DBT fracture in low-carbon steel were shown via the stress−d^−1/2 map. The results quantitatively showed the superiority of α grain size for brittle fracture.     

Synthesis,Crystal Structure and Luminescent Property of Cd (II) Complex with N-Benzenesulphonyl-L-leucine

A new trinuclear Cd (II) complex [Cd₃(L)₆(2,2-bipyridine)₃] [L = N-phenylsulfonyl-L-leucinato] has been synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The results show that the complex belongs to the orthorhombic, space group P2₁2₁2₁ with a = 16.877(3) Å, b = 22.875(5) Å, c = 29.495(6) Å, α = β = γ = 90°, V = 11387(4) ų, Z = 4, D_c= 1.416 μg·m⁻³, μ = 0.737 mm⁻¹, F (000) = 4992, and final R₁ = 0.0390, ωR₂ = 0.0989. The complex comprises two seven-coordinated Cd (II) atoms, with a N₂O₅ distorted pengonal bipyramidal coordination environment and a six-coordinated Cd (II) atom, with a N₂O₄ distorted octahedral coordination environment. The molecules form one dimensional chain structure by the interaction of bridged carboxylato groups, hydrogen bonds and π-π interaction of 2,2-bipyridine. The luminescent properties of the Cd (II) complex and N-Benzenesulphonyl-L-leucine in solid and in CH₃OH solution also have been investigated.     

Volume Elastic Modulus,Vascular Function,and Vascular Structure in Patients with Cardiovascular Risk Factors

Aims: Volume elastic modulus (V _E ), an index of arterial elasticity, and arterial diameter of the brachial artery can be automatically measured by a newly developed oscillometric device. We investigated the associations of V _E with flow-mediated vasodilation (FMD), an index of endothelium-dependent vasodilation, nitroglycerine-induced vasodilation (NID), an index of endothelium-independent vasodilation, and intima-media thickness (IMT) of the brachial artery and association of oscillometrically measured brachial artery diameter with ultrasonographically measured brachial artery diameter in patients with cardiovascular risk factors. Methods: Oscillometric measurements of V _E and brachial artery diameter and ultrasound measurements of brachial artery diameter, FMD, NID, and IMT of the brachial artery were performed in 50 patients with cardiovascular risk factors. Results: The mean values were 2.1±0.4 mmHg/% for V _E , 0.31±0.05 mm for brachial IMT, 4.48±0.70 mm for oscillometric brachial artery diameter, and 4.30±0.55 mm for ultrasound brachial artery diameter. V _E significantly correlated with brachial IMT (r=0.51, P ＜0.001), whereas there was no significant correlation of V _E with FMD (r=-0.08, P =0.58) or NID (r=0.07, P =0.61). Multivariate analysis revealed that V _E was significantly associated with brachial IMT (β=0.33, P =0.04). Oscillometric brachial artery diameter significantly correlated with ultrasound brachial artery diameter (r=0.79, P ＜0.001). The Bland-Altman plot showed good agreement between oscillometric brachial artery diameter and ultrasound brachial artery diameter (mean difference, -0.17 mm; limits of agreement, -1.03 mm to 0.69 mm). Conclusions: In patients with cardiovascular risk factors, V _E may represent atherosclerotic structural alterations of the vascular wall but not vascular function. The accuracy of oscillometric measurement of brachial artery diameter is acceptable.     

High Mechanic Enhancement of Chopped Carbon Fiber Reinforced-Low-Density Unsaturated Polyester Resin Composite at Low Preparation Temperature with Facile Polymerization

Chopped carbon fiber-reinforced low-density unsaturated polyester resin (CCFR-LDUPR) composite materials with light weight and high mechanical properties were prepared at low temperature and under the synergistic action of methyl ethyl ketone peroxide (MEKP-II) and cobalt naphthenate. Optimal preparation conditions were obtained through an orthogonal experiment, which were preparation temperature at 58.0 °C, 2.00 parts per hundred of resin (phr) of NH₄HCO₃, 4.00 phr of chopped carbon fibers (CCFs) in a length of 6.0 mm, 1.25 phr of initiator and 0.08 phr of cobalt naphthenate. CCFR-LDUPR composite sample presented its optimal properties for which the density (ρ) was 0.58 ± 0.02 g·cm⁻³ and the specific compressive strength (P_s) was 53.56 ± 0.83 MPa·g⁻¹·cm³, which is 38.9% higher than that of chopped glass fiber-reinforced low-density unsaturated polyester resin (CGFR-LDUPR) composite materials. Synergistic effects of initiator and accelerator accelerated the specific polymerization of resin in facile preparation at low temperature. Unique “dimples”, “plate microstructure” and “surface defect” fabricated the specific microstructure of the matrix of CCFR-LDUPR composite samples, which was different from that of cured unsaturated polyester resin (UPR) with “body defect” or that of CGFR-LDUPR with coexistence of “surface defect” and “body defect”.     

Adhesion of Resin-Resin and Resin–Lithium Disilicate Ceramic: A Methodological Assessment

The aim of this study was to evaluate four test methods on the adhesion of resin composite to resin composite, and resin composite to glass ceramic. Resin composite specimens (N = 180, Quadrant Universal LC) were obtained and distributed randomly to test the adhesion of resin composite material and to ceramic materials (IPS e.max CAD) using one of the four following tests: (a) Macroshear SBT: (n = 30), (b) macrotensile TBT: (n = 30), (c) microshear µSBT: (n = 30) and (d) microtensile µTBT test (n = 6, composite-composite:216 sticks, ceramic-composite:216 sticks). Bonded specimens were stored for 24 h at 23 °C. Bond strength values were measured using a universal testing machine (1 mm/min), and failure types were analysed after debonding. Data were analysed using Univariate and Tukey’s, Bonneferroni post hoc test (α = 0.05). Two-parameter Weibull modulus, scale (m), and shape (₀) were calculated. Test method and substrate type significantly affected the bond strength results, as well as their interaction term (p < 0.05). Resin composite to resin composite adhesion using SBT (24.4 ± 5)^a, TBT (16.1 ± 4.4)^b and µSBT (20.6 ± 7.4)^a,b test methods presented significantly lower mean bond values (MPa), compared to µTBT (36.7 ± 8.9)^b (p < 0.05). When testing adhesion of glass ceramics to resin composite, µSBT (6.6 ± 1)^B showed the lowest and µTBT (24.8 ± 7)^C,D the highest test values (MPa) (SBT (14.6 ± 5)^A,D and TBT (19.9 ± 5)^A,B) (p < 0.05). Resin composite adhesion to ceramic vs. resin composite did show significant difference for the test methods SBT and µTBT (resin composite (24.4 ± 5; 36.7 ± 9 MPa) vs. glass ceramic (14.6 ± 5; 25 ± 7 MPa)) (p > 0.05). Among substrate–test combinations, Weibull distribution presented the highest shape values for ceramic–resin in µSBT (7.6) and resin–resin in µSBT (5.7). Cohesive failures in resin–resin bond were most frequently observed in SBT (87%), followed by TBT (50%) and µSBT (50%), while mixed failures occurred mostly in ceramic–resin bonds in the SBT (100%), TBT (90%), and µSBT (90%) test types. According to Weibull modulus, failure types, and bond strength, µTBT tests might be more reliable for testing resin-based composites adhesion to resin, while µSBT might be more suitable for adhesion testing of resin-based composites to ceramic materials.     

Crystal and molecular structure of n,n'-diethyl-n,n'-diphenylurea

N,N′-diphenyl-N,N′-diethylurea (C₁₇H₂₀N₂O) crystallizes in the space group P2₁/c. The unit cell constants are: a = 10.42 ± 0.01 Å, b = 16.86 ± 0.02 Å, c = 10.66 ± 0.001 Å, β = 125°16′ ± 5′; Z = 4, D_x = 1.16 g·cm^-3, D_meas = 1.16 ± 0.01 g·cm^-3. Data for 1392 reflections were collected at room temperature on a Picker automated diffractometer. The crystal structure was solved by direct methods and refined by bloc-diagonalized matrix least-squares calculations. The molecule is characterized by a pseudo C₂ symmetry; both phenyl groups are trans with respect to the oxygen atom. The hybridization of the two nitrogen atoms is intermediate between trigonal and tetrahedral; the nonplanar distortion of the amide groups is about 30°. The amide C-N bond lengths are 1.37 Å.     

Structure and Properties of Heat-Resistant Alloys NiAl–Cr–Co–X (X = La,Mo, Zr,Ta, Re) and Fabrication of Powders for Additive Manufacturing

The NiAl–Cr–Co–X alloys were produced by centrifugal self-propagating high-temperature synthesis (SHS) casting. The effects of dopants X = La, Mo, Zr, Ta, and Re on combustion, as well as the phase composition, structure, and properties of the resulting cast alloys, have been studied. The greatest improvement in overall properties was achieved when the alloys were co-doped with 15% Mo and 1.5% Re. By forming a ductile matrix, molybdenum enhanced strength characteristics up to the values σ_ucs = 1604 ± 80 MPa, σ_ys = 1520 ± 80 MPa, and ε_pd = 0.79%, while annealing at T = 1250 ℃ and t = 180 min improved strength characteristics to the following level: σ_ucs = 1800 ± 80 MPa, σ_ys = 1670 ± 80 MPa, and ε_pd = 1.58%. Rhenium modified the structure of the alloy and further improved its properties. The mechanical properties of the NiAl, ZrNi₅, Ni_0.92Ta_0.08, (Al,Ta)Ni₃, and Al(Re,Ni)₃ phases were determined by nanoindentation. The three-level hierarchical structure of the NiAl–Cr–Co+15%Mo alloy was identified. The optimal plasma treatment regime was identified, and narrow-fraction powders (fraction 8–27 µm) characterized by 95% degree of spheroidization and the content of nanosized fraction <5% were obtained.     

Alternating electron and proton transfer steps in photosynthetic water oxidation

Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel–production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese–calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S₂ → S₃ transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (). The rate-determining elementary step (τ, approximately 30 µs at 20 °C) in the long-distance proton relocation toward the protein–water interface is characterized by a high activation energy (E_a = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S₀ → S₁ transition are similar (τ, approximately 100 µs; E_a = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established.     

Effects of non-steroidal anti-inflammatory drugs and prostaglandins on alkali secretion by rabbit gastric fundus in vitro

The effects of non-steroidal anti-inflammatory drugs and prostaglandins E₂ and F_2α on the secretory and electrical activity of isolated rabbit fundic mucosa have been studied. Spontaneous acid secretion was inhibited by serosal side application of sodium thiocyanate (6×10⁻²M) and the resulting alkali secretion measured by pH stat tiration. Serosal side application of indomethacin (10⁻⁵M) or aspirin (3×10⁻³M) inhibited alkali secretion (0·55±0·06 to 0·12±0·06 μmol/cm²/h, n=6, p<0·01 and 0·28±0·06 to 0·11±0·03 μmol/cm²/h, n=7, p<0·02 respectively). Mucosal or serosal side prostaglandin E₂ (10⁻⁵ to 10⁻¹⁰M) and F_2α (10⁻⁴ to 10⁻¹⁰M) failed to alter the rate of alkalinisation but secretion was significantly increased by serosal side 16,16-dimethyl-prostaglandin E₂ (10⁻⁶M) (0·90±0·20 to 1·50±0·30 μmol/cm²/h, n=6, p<0·01). Serosal side application of 10⁻⁶M prostaglandin E₂ to fundic mucosae pretreated with either aspirin (5×10⁻³M) or indomethacin (10⁻⁵M), to reduce endogenous E₂ formation, also failed to alter alkali secretion. Pretreatment of the mucosa with 16,16-dimethyl-E₂ (10⁻⁶M) abolished the inhibitory effect of indomethacin (10⁻⁵M) on alkali secretion (n=6) but did not modify the secretory response to aspirin (3×10⁻³M) (fall in alkali secretion with aspirin = 81±11% and with aspirin plus 16,16-dimethyl-E₂ = 72±10%, n=7). In the doses used, none of the prostaglandins or non-steroidal anti-inflammatory drugs altered transmucosal potential difference or electrical resistance. These results show that the damaging agents, aspirin and indomethacin, both inhibit gastric alkali secretion but that modes of action may differ. The observation that prostaglandins, E₂ and F_2α failed to increase alkali production suggests that their protective activity against a variety of damaging agents as shown by others, may be mediated by another mechanism.     

Differential contribution of HLA-DR,DQ, and TAP2 alleles to systemic lupus erythematosus susceptibility in Spanish patients: role of TAP2*01 alleles in Ro autoantibody production

OBJECTIVE—To study the influence MHC class II and TAP2 alleles exert on systemic lupus erythematosus (SLE) susceptibility and on the clinical and serological manifestations of the disease, in a cohort of Spanish patients.
METHODS—HLA-DR serological typing and HLA-DQA, DQB, and TAP2 DNA sequence specific oligotyping, were carried out in 85 unrelated Spanish SLE patients and 186 healthy controls. Autoantibodies detection was carried out by indirect immunofluorescence and counter immunoelectrophoresis.
RESULTS—Total SLE group: the frequency of HLA-DR3 and HLA-DQA1*0501 is significantly increased in this group (p_c<0.005, δ=0.34 and p_c<0.005, δ= 0.45, respectively) although the highest δ value (δ=0.87) is obtained when the TAP2*01 alleles are considered. No DQB allele shows significant deviation from the control group. Renal damage: it mainly occurs in HLA-DR3 patients (p_c<0.0005 and δ=0.72). HLA-DQA1*0501 (p_c<0.05, δ=0.57) and DQB1*0201 (p_c NS, δ=0.56) are weaker susceptibility factors. Ro+ (but not La) group: this autoantibody response is associated with TAP2*01 alleles in homozygosity (p<0.05, δ=0.81). Ro/La+ group: it has a different genetic background as HLA-DQA1*0501 (δ=1) and HLA-DQB1*0201 (δ=1) are the main susceptibility factors.
CONCLUSIONS—A differential association between HLA-DR, DQA1, and DQB1 alleles and SLE or its clinical and serological manifestations are found. Furthermore, the associations are different to the ones reported in other ethnic groups. Finally, TAP2*01 group of alleles are associated with the highest susceptibility to SLE (higher than HLA-DR3) and may influence Ro (but not La) autoantibodies production, whereas HLA-DQA1*0501 and DQB1*0201 mediates concomitant Ro and La production.

     

Synthesis,Crystal Structure and Luminescent Property of Mg(II) Complex with N-Benzenesulphonyl-L-Leucine and 1,10-Phenanthroline

A new complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ [L= N-benzenesulphonyl-L-leucine] was synthesized by the reaction of magnesium chloride hexahydrate with N-benzenesulphonyl-L-leucine and 1,10-phenanthroline in the CH₃CH₂OH/H₂O (v:v = 5:1). It was characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The crystal of the title complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ belongs to triclinic, space group P-1 with a = 0.72772(15) nm, b = 1.4279(3) nm, c = 1.4418(3) nm, α = 63.53(3)°, β = 79.75(3)°, γ = 81.83(3)°, V = 1.3163(5) nm³, Z =1, D_c= 1.258 μg·m⁻³, μ = 0.177 mm⁻¹, F(000) = 526, and final R₁ = 0.0506, ωR₂ = 0.1328. The complex comprises a six-coordinated magnesium(II) center, with a N₂O₄ distorted octahedron coordination environment. The molecules are connected by hydrogen bonds and π-π stacking to form one dimensional chain structure. The luminescent property of the Mg(II) complex has been investigated in solid.     

Crystal Structures and Microwave Dielectric Properties of Novel MgCu2Nb2O8 Ceramics Prepared by Two-Step Sintering Technique

In this work, novel MgCu₂Nb₂O₈ (MCN) ceramics were synthesized by the two-step sintering (TSS) technique, and the phase composition, crystal structures, and microwave dielectric properties were comprehensively studied. X-ray diffraction (XRD) and Raman analysis demonstrated that MCN ceramics are multi-phase ceramics consisting of MgNb₂O₆ and CuO phases. X-ray photoelectron spectroscopy (XPS) was utilized to investigate the chemical composition and element valence of MgCu₂Nb₂O₈ ceramics. Scanning electron microscopy (SEM) analysis demonstrated dense microstructures in the MCN ceramics prepared at a sintering temperature of 925 °C. The microwave dielectric properties were largely affected by the lattice vibrational modes and densification level of the ceramics. The outstanding microwave dielectric properties of ε_r = 17.15, Q × f = 34.355 GHz, and τ_f = −22.5 ppm/°C were obtained for the MCN ceramics sintered at 925 °C, which are results that hold promise for low temperature co-fired ceramic (LTCC) applications.     

Intestinal barrier dysfunction is involved in the development of systemic inflammatory responses and lung injury in type A aortic dissection: a case-control study

BackgroundThe definite pathogenesis of lung injury complicated by type A aortic dissection (TAAD) remains unclear. In this paper, we investigated the relationship between intestinal injury, lung injury, and systemic inflammatory responses, with the aim of exploring the mechanism underlying intestinal injury and its impact on systemic inflammatory responses and lung injury in patients with TAAD.MethodsPatients with TAAD (n=36) and those with aortic root aneurysm (ARA) (n=30) were compared. TAAD patients were younger and had higher creatinine (Cr) than ARA patients. White blood cell (WBC) count, neutrophil count, neutrophil percentage, interleukin (IL)-6, IL-8, tumor necrosis factor α (TNF-α), C-reactive protein (CRP), histamine (HIS) levels, PaO₂-FiO₂ ratio, diamine oxidase (DAO), intestinal fatty acid binding protein (iFABP), and peptidoglycan (PGN) were measured using the same laboratory methods between the two groups.ResultsIncreased WBC [(9.70±4.05)×10⁹/L vs. (5.88±1.2)×10⁹/L, P<0.001], neutrophil [(7.65±4.27)×10⁹/L vs. (3.40±0.97)×10⁹/L, P<0.001], neutrophil percentage [(74.73±13.42)% vs. (57.67±9.45)%, P<0.001], IL-6 (37.48±4.87 vs. 20.90±0.92 pg/mL, P<0.001), IL-8 (97.15±9.11 vs. 69.46±3.17 pg/mL, P<0.001), TNF-α (71.32±10.35 vs. 33.90±2.27 pg/mL, P<0.001), CRP (10.67±1.62 vs. 4.43±0.26 µg/mL, P<0.001), HIS (13.29±1.88 vs. 7.63±0.58 ng/mL, P<0.001), DAO (24.94±4.72 vs. 10.92±2.44 U/L, P<0.001), iFABP (879.01±190.12 vs. 206.35±42.20 pg/mL, P<0.001), and PGN (31.10±5.51 vs. 12.52±2.20 ng/mL, P<0.001) and decreased PaO₂-FiO₂ ratio (365.35±146.47 vs. 447.86±70.80 mmHg, P=0.01) were detected in TAAD group relative to ARA group. In TAAD group, positive correlations were detected between DAO and inflammatory cytokines [IL-6 (r=0.56, P<0.001), IL-8 (r=0.61, P<0.001), TNF-α (r=0.71, P<0.001), and CRP (r=0.68, P<0.001)], between iFABP and inflammatory cytokines [IL-6 (r=0.72, P<0.001), IL-8 (r=0.71, P<0.001), TNF-α (r=0.90, P<0.001), and CRP (r=0.89, P<0.001)], between DAO and PGN (r=0.52, P<0.001), between iFABP and PGN (r=0.74, P<0.001), between PGN and inflammatory cytokines [IL-6 (r=0.85, P<0.001), IL-8 (r=0.44, P<0.001), TNF-α (r=0.61, P<0.001), and CRP (r=0.73, P<0.001)]. In acute TAAD subgroup, PGN and PaO₂-FiO₂ ratio were negatively correlated (r=−0.50, P=0.036).ConclusionsSystemic inflammatory responses in TAAD patients may lead to lung and intestine injury, and the latter may be involved in the development of systemic inflammatory responses and lung injury in these patients.     

Peculiarities of DRX in a Highly-Alloyed Austenitic Stainless Steel

The features of discontinuous dynamic recrystallization (DRX) in a highly-alloyed austenitic stainless steel were studied at temperatures of 800 °C to 1100 °C. Hot deformation accompanied by DRX was characterized by an activation energy of 415 kJ/mol. The frequency of the sequential DRX cycles depended on the deformation conditions; and the largest fraction of DRX grains with small grain orientation spread below 1° was observed at a temperature of around 1000 °C and a strain rate of about 10⁻³ s⁻¹. The following power law relationships were obtained for DRX grain size (D_DRX) and dislocation density (ρ) vs. temperature-compensated strain rate (Z) or peak flow stress (σ_P): D_DRX ~ Z^−0.25, ρ ~ Z^0.1, σ_P ~ D_DRX^−0.9, σ_P ~ ρ^1.4. The latter, i.e., σ_P ~ ρ^1.4, was valid in the flow stress range below 300 MPa and changed to σ_P ~ ρ^0.5 on increasing the stress. The obtained dependencies suggest a unique power law function between the dislocation density and the DRX grain size with an exponent of −0.5.     

An attempt to distinguish between the actions of neuromuscular blocking drugs on the acetylcholine receptor and on its associated ionic channel

The effects of lobeline and tubocurarine on the voltage-clamped endplates of frog sartorius and cutaneous pectoris muscles were examined at room temperature (20-23°C). Like tubocurarine, lobeline causes nondepolarizing neuromuscular blockade. The half-time of decay (t_½) of endplate currents (e.p.c.s) recorded at a holding potential (V_m) of -90 mV was significantly shorter in endplates treated with lobeline (50 μM; mean t_½ ± SEM = 0.41 ± 0.02 ms) or tubocurarine (11.4 μM; t_½ = 0.64 ± 0.04 ms) than in those treated with Mg²⁺ (13 mM; t_½ = 1.39 ± 0.11 ms) or a low concentration of tubocurarine (3 μM; t_½ = 0.87 ± 0.05 ms). Similarly, lobeline (10 μM) shortened the t_½ of untreated miniature e.p.c.s by 35%; tubocurarine, however, abolished miniature e.p.c.s at the concentration required to observe its actions on e.p.c. decay kinetics. The t_½ of e.p.c.s recorded from preparations treated with Mg²⁺ (13 mM), tubocurarine at low concentrations (3 μM), or untreated miniature e.p.c.s was logarithmically related to V_m, being slower at more hyperpolarized values. By contrast, the t_½s of e.p.c.s recorded in either lobeline (50 μM) or tubocurarine (11.4 μM) were independent of voltage in the range -150 to -80 mV. The ability of lobeline to shorten t_½ and to remove the voltage dependence of t_½ was partially antagonized by Mg²⁺ (13 mM). As expected, when lobeline or tubocurarine was removed from the bath or when acetylcholine release from the motor nerve terminals was increased by 4-aminopyridine (20 μM) and Ca²⁺ (10 mM) (in the presence of lobeline or tubocurarine), the amplitude of e.p.c.s increased as a function of time. However, the t_½ of the decay phase of the e.p.c.s remained shortened (i.e., unaltered from the earlier treatment). These results suggest that both tubocurarine and lobeline have at least two distinct postjunctional actions including: (i) a block of the acetylcholine receptor and (ii) a block of the ionic channel associated with the acetylcholine receptor.     

Picosecond kinetics of fluorescence and absorbance changes in photosystem II particles excited at low photon density

Oxygen-evolving photosystem II particles (from Synechococcus) with about 80 chlorophyll molecules per primary electron donor (P₆₈₀) were used for a correlated study of picosecond kinetics of fluorescence and absorbance changes, detected by the single-photon-timing technique and by a pump-probe apparatus, respectively. Chlorophyll fluorescence decays were biexponential with lifetimes τ₁ = 80 ± 20 ps and τ₂ = 520 ± 120 ps in open reaction centers and τ₁ = 220 ± 30 ps and τ₂ = 1.3 ± 0.15 ns in closed reaction centers. The corresponding fluorescence yield ratio F_max/F_o was 3-4. Absorbance changes were monitored in the spectral range of 620-700 nm after excitation at 675 nm with 10-ps pulses sufficiently weak (<7 × 10¹² photons/cm² per pulse) to avoid singlet-singlet annihilation. With open reaction centers, the absorbance changes could be fit to the sum of three exponentials. The associated absorbance difference spectra were attributed to (i) exciton trapping and charge separation (τ = 100 ± 20 ps), (ii) the electron-transfer step P₆₈₀⁺ I^- Q_A → P₆₈₀⁺ I Q_A^- (where I is the primary electron acceptor and Q_A is the first quinone acceptor) (τ = 510 ± 50 ps), and (iii) the reduction of P₆₈₀⁺ by the intact donor side (τ > 10 ns). With closed reaction centers, the absorbance changes were biexponential with lifetimes τ₁ = 170-260 ps and τ₂ = 1.6-1.75 ns. The results are explained in terms of a kinetic model that assumes P₆₈₀ to constitute a shallow trap. The results show that Q_A reduction in these photosystem II particles decreases both the apparent rate and the yield of the primary charge separation by a factor of 2-3 and increases the mean lifetime of excitons in the antenna by a factor of 3-4. Thus, we conclude that the long-lived, nanosecond chlorophyll fluorescence is not charge-recombination luminescence but rather emission from equilibrated excited states of antenna chlorophylls.     

Tcra gene recombination is supported by a Tcra enhancer- and CTCF-dependent chromatin hub

Antigen receptor locus V(D)J recombination requires interactions between widely separated variable (V), diversity (D), and joining (J) gene segments, but the mechanisms that generate these interactions are not well understood. Here we assessed mechanisms that direct developmental stage-specific long-distance interactions at the Tcra/Tcrd locus. The Tcra/Tcrd locus recombines Tcrd gene segments in CD4⁻CD8⁻ double-negative thymocytes and Tcra gene segments in CD4⁺CD8⁺ double-positive thymocytes. Initial V_α-to-J_α recombination occurs within a chromosomal domain that displays a contracted conformation in both thymocyte subsets. We used chromosome conformation capture to demonstrate that the Tcra enhancer (E_α) interacts directly with V_α and J_α gene segments distributed across this domain, specifically in double-positive thymocytes. Moreover, E_α promotes interactions between these V_α and J_α segments that should facilitate their synapsis. We found that the CCCTC-binding factor (CTCF) binds to E_α and to many locus promoters, biases E_α to interact with these promoters, and is required for efficient V_α–J_α recombination. Our data indicate that E_α and CTCF cooperate to create a developmentally regulated chromatin hub that supports V_α–J_α synapsis and recombination.     

Fatty acids suppress voltage-gated Na+ currents in HEK293t cells transfected with the α-subunit of the human cardiac Na+ channel

Studies have shown that fish oils, containing n-3 fatty acids, have protective effects against ischemia-induced, fatal cardiac arrhythmias in animals and perhaps in humans. In this study we used the whole-cell voltage-clamp technique to assess the effects of dietary, free long-chain fatty acids on the Na⁺ current (I_Na,α) in human embryonic kidney (HEK293t) cells transfected with the α-subunit of the human cardiac Na⁺ channel (hH1_α). Extracellular application of 0.01 to 30 μM eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced I_Na,α with an IC₅₀ of 0.51 ± 0.06 μM. The EPA-induced suppression of I_Na,α was concentration- and voltage-dependent. EPA at 5 μM significantly shifted the steady-state inactivation relationship by −27.8 ± 1.2 mV (n = 6, P < 0.0001) at the V_1/2 point. In addition, EPA blocked I_Na,α with a higher “binding affinity” to hH1_α channels in the inactivated state than in the resting state. The transition from the resting state to the inactivated state was markedly accelerated in the presence of 5 μM EPA. The time for 50% recovery from the inactivation state was significantly slower in the presence of 5 μM EPA, from 2.1 ± 0.8 ms for control to 34.8 ± 2.1 ms (n = 5, P < 0.001). The effects of EPA on I_Na,α were reversible. Furthermore, docosahexaenoic acid (C22:6n-3), α-linolenic acid (C18:3n-3), conjugated linoleic acid (C18:2n-7), and oleic acid (C18:1n-9) at 5 μM and all-trans-retinoic acid at 10 μM had similar effects on I_Na,α as EPA. Even 5 μM of stearic acid (C18:0) or palmitic acid (C16:0) also significantly inhibited I_Na,α. In contrast, 5 μM EPA ethyl ester did not alter I_Na,α (8 ± 4%, n = 8, P > 0.05). The present data demonstrate that free fatty acids suppress I_Na,α with high “binding affinity” to hH1_α channels in the inactivated state and prolong the duration of recovery from inactivation.