Rates and equilibria at the acetylcholine receptor of electrophorus electroplaques. A study of neurally evoked postsynaptic currents and of voltage-jump relaxations

Kinetic measurements are employed to reconstruct the steady-state activation of acetylcholine [Ach] receptor channels in electrophorus electroplaques. Neurally evoked postsynaptic currents (PSCs) decay exponentially; at 15 degrees C the rate constant, α, equals 1.2 ms(-1) at 0 mV and decreases e-fold for every 86 mV as the membrane voltage is made more negative. Voltage-jump relaxations have been measured with bath-applied ACh, decamethonium, carbachol, or suberylcholine. We interpret the reciprocal relaxation time 1/τ as the sum of the rate constant α for channel closing and a first-order rate constant for channel opening. Where measureable, the opening rate increases linearly with [agonist] and does not vary with voltage. The voltage sensitivity of small steady-state conductances (e- fold for 86 mV) equals that of the closing rate α, confirming that the opening rate has little or no additional voltage sensitivity. Exposure to α-bungarotoxin irreversibly decreases the agonist-induced conductance but does not affect the relaxation kinetics. Tubocurarine reversibly reduces both the conductance and the opening rate. In the simultaneous presence of two agonist species, voltage-jump relaxations have at least two exponential components. The data are fit by a model in which (a) the channel opens as the receptor binds the second in a sequence of two agonist molecules, with a forward rate constant to 10(7) to 2x10(8) M(-1)s(-1); and (b) the channel then closes as either agonist molecule dissociates, with a voltage-dependent rate constant of 10(2) to 3x10(3)s(-1).     

Activities of Various Peptidases in the First Leaf of Wheat

In the first leaf of wheat (Triticum aestivum L. cv. Capelle) the content of soluble protein diminished to about 50% of the initial value between the 7th and the 19th day after sowing. In order to understand proteolysis in the leaves, the activities of several peptidases were measured in extracts from leaves at four different ages. The carboxypeptidase activities increased during the growth of the leaves, and then began to decrease. The activities of the alkaline peptidases increased, while that of the benzoyl-DL-arginine-p-nitroanilide (BAPA) hydrolysing enzyme decreased during the whole period studied. The “naphthylamidase” activities showed first a slow rise, but then leveled off. Two bands with naphthylamidase activity could be detected after disc electrophoresis. All the peptidases studied were present in the leaves at rather high concentrations. This indicates that they all may participate in the hydrolysis of leaf proteins into free amino acids.     

INSULIN PRODUCES A BIPHASIC RESPONSE INTETRAHYMENA THERMOPHILABY STIMULATING CELL SURVIVAL AND ACTIVATING PROLIFERATION IN TWO SEPARATE CONCENTRATION INTERVALS

Cells ofTetrahymenamay produce autocrine signal molecules with effects on survival and proliferation. Here we have tested the effects of human recombinant and bovine insulin, and the B22–B30 fragment of bovine insulin over a wide range of concentrations (10^?5–10^?18m ) on cell survival and proliferation in a synthetic nutrient medium. The cells were grown in conical flasks at low initial cell densities (40 and 400cells/ml). Insulin prevented rapid cell death and/or promoted cell proliferation over two separate concentration ranges: down to nanomolar levels and again in the low pico- and femtomolar range. At an initial population density of 400cells/ml the cells multiplied at both concentration intervals. At 40 or fewer organisms/ml the cells multiplied in the high concentration interval, whereas in the low interval they survived for about four times longer than those in the control cultures. B22–B30 added to cultures of 40 initial cells/ml produced a stimulation of cell survival in the low pico- and high femtomolar range. In the presence of hemin (50nm ) cells at 400 initial organisms/ml multiplied at insulin concentrations down to about 3nm and again from 300am to 10pm . In some cases, hemin plus insulin activated cell proliferation between the two concentration intervals as well. At 40cells/ml the cells not only survived but proliferated in the femtomolar range. Cells in cultures supplemented with both hemin and B22–B30 multiplied at the low concentration interval (from about 100fm to 10pm ).     

Benzo[a]pyrene, 3-methylcholanthrene and beta-naphthoflavone induce oxidative stress in hepatoma hepa 1c1c7 Cells by an AHR-dependent pathway

Polycyclic aromatic hydrocarbons have been shown to cause oxidative stress in vitro and in vivo in various animal models but the mechanisms by which these compounds produce oxidative stress are unknown. In the current study we have investigated the role of the aryl hydrocarbon receptor (AHR) in the production of reactive oxygen species (ROS) by its cognate ligands and the consequent effect on cyp1a1 activity, mRNA and protein expressions. For this purpose, Hepa 1c1c7 cells wild-type (WT) and C12 mutant cells, which are AHR-deficient, were incubated with increasing concentrations of the AHR-ligands, benzo[a]pyrene (B[a]P, 0.25-25 μM), 3-methylcholanthrene (3MC, 0.1-10 μM) and β-naphthoflavone (βNF, 1-50 μM). The studied AHR-ligands dose-dependently increased lipid peroxidation in WT but not in C12 cells. However, only B[a]P and βNF, at the highest concentrations tested, significantly increased H₂O₂ production in WT but not C12 cells. The increase in lipid peroxidation and H₂O₂ production by AHR-ligands were accompanied by a decrease in the cyp1a1 catalytic activity but not mRNA or protein expressions, which were significantly induced in a dose-dependent manner by all AHR-ligands, suggesting a post-translational mechanism is involved in the decrease of cyp1a1 activity. The AHR-ligand-mediated decrease in cyp1a1 activity was reversed by the antioxidant N-acetylcysteine. Our results show that the AHR-ligands induce oxidative stress by an AHR-dependent pathway.     

Student perspectives of assessment by TEMM model in physiology

Assessment is the process by which the teacher and the student gain knowledge about student progress. Assessment systems should aim at evaluating the desired learning outcomes. In Melaka Manipal Medical College, (Manipal Campus), Manipal, India, the TEMM model (consisting of 4 assessment methods: Triple Jump Test, essay incorporating critical thinking questions, Multistation Integrated Practical Examination, and multiple choice questions) was introduced to 30 refresher students in the fourth block of the academic year. At the end of the block, a questionnaire was distributed to ask the students to rank the different assessments in the order of their preference with respect to seven items. Analysis of the results showed that not a single type of assessment was ranked highest for all the seven items, proving the earlier observation that a single assessment does not fulfill all aspects of assessment and that there is a need for an evaluating system with multiple ways of assessment.     

Sixty simple sequence repeat markers for use in the Festuca–Lolium complex of grasses

So far only very few simple sequence repeat (SSR) markers developed from grass species have had their primer sequences published. To make more markers available to the scientific community, we isolated and sequenced 256 microsatellite‐containing clones from four genome libraries of a Lolium multiflorum×Festuca glaucescens F₁ hybrid following enrichment in (TC)_n, (TG)_n, or both repeats. In this work, we report the primer sequences of 60 SSRs including preliminary results of polymorphism for mapping.     

Molecular identification of Campanulotes bidentatus Scopoli, 1763 (Phthiraptera,Philopteridae) infecting the domestic pigeon Columba livia from Saudi Arabia

The taxonomy of the order Phthiraptera is unstable and still problematic to researchers. Most of the current taxon classifications are mainly based on morphological features. Campanulotes bidentatus belongs to the chewing lice of the Philopteridae family that mostly parasitic on birds. There is a lack of sequence data and phylogenetic analyses on the family Philopteridae. In the current study, C. bidentatus was collected from the domestic pigeon Columba livia and identified morphologically and molecularly based on the mitochondrial cytochrome c oxidase subunit 1 gene (COI). The infection rate of the Campanulotes genus was approximately 58.82% in this study. Phylogenetic analysis based on the mt COI gene was informative for members of Philopteridae and the group taxon genera formed distinct clades. Future studies were recommended using the 16s rRNA to enhance the tree topology and obtain clear differentiation between genera.     

Employment of Cassia angustifolia leaf extract for zinc nanoparticles fabrication and their antibacterial and cytotoxicity

The plant Cassia angustifolia belongs to Saudi Arabia, which is one of the native places and now cultured throughout the global countries. Medical care in the Arab world is an essential outlet for medicinal plants, both because they are crucial elements for prophetic medicine and due to their lengthy background in the Middle East. C.angustifolia is one of the medicinal plants used in the Saudi Arabia. The usage of plant extracts for synthesizing nanoparticles is conducive to other biological material, since it avoids the lengthy phase of cell culture maintenance. Silver nanoparticles attract further attention due to their strong conductivity, stability and antimicrobial activity across different metal nanoparticles. The present study was designed in the Saudi C. angustifolia leaves with the zinc synthesis of nanoparticles and its antibacterial ability. The plant extracts of C. angustifolia was used for synthesis of zinc nanoparticles, antimicrobial activities against bacterial strains have been tested along with transmission electron microscope (TEM), UV spectroscopy and antimicrobial activities have been conducted. This study showed that silver ions may be transferred from the plant extract to silver nanoparticles. AgNPs biogenic capacity to antibacterial with lovo cell with IC₅₀ ranged from 33.5 ± 0.2 μg/mL demonstrated strong antibacterial capacity to antibody. The overall absorption value for the extract was between 420 and 440 nm and the color transition to green was the plasma absorption of the AgNPs. TEM results was showed in 200,000 magnification. The uniqueness of the current study is that Cassia angustifolia leaf extract from Saudi Arabia was used to prepare the metallic nanoparticles. Additionally, ZnCl₂ may also be used as nanoparticles of mineral salt and zinc, which, since their application has been confirmed, are antimicrobial.     

Sepsis impairs alveolar epithelial function by downregulating Na-K-ATPase pump

Widespread vascular endothelial injury is the major mechanism for multiorgan dysfunction in sepsis. Following this process, the permeability of the alveolar capillaries is augmented with subsequent increase in water content and acute respiratory distress syndrome (ARDS). Nevertheless, the role of alveolar epithelium is less known. Therefore, we examined alveolar fluid clearance (AFC) using isolated perfused rat lung model in septic rats without ARDS. Sepsis was induced by ligating and puncturing the cecum with a 21-gauge needle. AFC was examined 24 and 48 h later. The expression of Na-K-ATPase proteins was examined in type II alveolar epithelial cells (ATII) and basolateral membrane (BLM). The rate of AFC in control rats was 0.51 ± 0.02 ml/h (means ± SE) and decreased to 0.3 ± 0.02 and 0.33 ± 0.03 ml/h in 24 and 48 h after sepsis induction, respectively (P < 0.0001). Amiloride, significantly decreased AFC in sepsis; conversely, isoproterenol reversed the inhibitory effect of sepsis. The alveolar-capillary barrier in septic rats was intact; therefore the finding of increased extravascular lung water in early sepsis could be attributed to accumulation of protein-poor fluid. The expression of epithelial sodium channel and Na-K-ATPase proteins in whole ATII cells was not different in both cecal ligation and puncture and control groups; however, the abundance of Na-K-ATPase proteins was significantly decreased in BLMs of ATII cells in sepsis. Early decrease in AFC in remote sepsis is probably related to endocytosis of the Na-K-ATPase proteins from the cell plasma membrane into intracellular pools, with resultant inhibition of active sodium transport in ATII cells.