Glutathione accelerates sodium channel inactivation in excised rat axonal membrane patches

The effects of glutathione were studied on the gating behaviour of sodium channels in membrane patches of rat axons. Depolarizing pulses from –120 to –40 mV elicited sodium currents of up to 500 pA, indicating the simultaneous activation of up to 250 sodium channels. Inactivation of these channels in the excised, inside-out configuration was fitted by two time constants ( h1=0.81 ms; h2= 5.03 ms) and open time histograms at 0 mV revealed a biexponential distribution of channel openings ( short=0.28 ms; long=3.68 ms). Both, the slow time constant of inactivation and the long lasting single channel openings disappeared after addition of the reducing agent glutathione (2–5 mM) to the bathing solution. Sodium channels of excised patches with glutathione present on the cytoplasmatic face of the membrane had inactivation kinetics similar to channels recorded in the cell-attached configuration. These observations indicate that redox processes may contribute to the gating of axonal sodium channels

Orientational Effects and Random Mixing in 1-Alkanol + Alkanone Mixtures

1-Alkanol + alkanone systems have been investigated through the data analysis of molar excess functions, enthalpies, isobaric heat capacities, volumes and entropies, and using the Flory model and the formalism of the concentrationconcentration structure factor (SCC(0)). The enthalpy of the hydroxyl-carbonyl interactions has been evaluated. These interactions are stronger in mixtures with shorter alcohols (methanol-1-butanol) and 2-propanone or 2-butanone. However, effects related to the self-association of alcohols and to solvation between unlike molecules are of minor importance when compared with those which arise from dipolar interactions. Physical interactions are more relevant in mixtures with longer 1-alkanols. The studied systems are characterized by large structural effects. The variation of the molar excess enthalpy with the alcohol size along systems with a given ketone or with the alkanone size in solutions with a given alcohol are discussed in terms of the different contributions to this excess function. Mixtures with methanol show rather large orientational effects. The random mixing hypothesis is attained to a large extent for mixtures with 1-alkanols ≠ methanol and 2-alkanones. Steric effects and cyclization lead to stronger orientational effects in mixtures with 3-pentanone, 4-heptanone, or cyclohexanone. The increase of temperature weakens orientational effects. Results from SCC(0) calculations show that homocoordination is predominant and support conclusions obtained from the Flory model.Ministerio de Ciencia e Innovación, under Project FIS2010-1695

Orientational Effects and Random Mixing in 1‑Alkanol + Nitrile Mixtures

1-Alkanol + alkanenitrile or + benzonitrile systems have been investigated by means of the molar excess functionsenthalpies (Hm E ), isobaric heat capacities (Cp,m E ), volumes (Vm E ), and entropiesand using the Flory model and the concentration−concentration structure factor (SCC(0)) formalism. From the analysis of the experimental data available in the literature, it is concluded that interactions are mainly of dipolar type. In addition, large Hm E values contrast with rather low Vm E values, indicating the existence of strong structural effects. Hm E measurements have been used to evaluate the enthalpy of the hydroxyl−nitrile interactions (ΔHOH−CN). They are stronger in methanol systems and become weaker when the alcohol size increases. In solutions with a given short chain 1-alkanol (up to 1-butanol), the replacement of ethanenitrile by butanenitrile weakens the mentioned interactions. Application of the Flory model shows that orientational effects exist in methanol or 1- nonanol, or 1-decanol + ethanenitrile mixtures. In the former solution, this is due to the existence of interactions between unlike molecules. For mixtures including 1-nonanol or 1-decanol, the systems at 298.15 K are close to their UCST (upper critical solution temperature), and interactions between like molecules are dominant. Orientational effects also are encountered in methanol or ethanol + butanenitrile mixtures because self-association of the alcohol plays a more important role. Aromaticity effect seems to enhance orientational effects. For the remainder of the systems under consideration, the random mixing hypothesis is attained to a rather large extent. Results from the application of the SCC(0) formalism show that homocoordination is the dominant trend in the investigated solutions, and are consistent with those obtained from the Flory model

DENSITY, COMPRESSIBILITY, SPECIFIC HEAT AND DIFFRACTION DATA OF LITHIUM-MAGNESIUM ALLOYS

For LiMg liquid alloys the density and the speed of ultrasonic waves were measured for temperatures between the liquidus and 970 ± 80 K, depending on the sample. The specific heat at constant pressure was determined for liquid and solid alloys at the compositions xMg < 0.50 and xMg < 0.60, respectively. The Scc (q) partial structure factor was measured by neutron diffraction in the liquid state at 695 and 875 K for the zero-alloy composition Li0.7Mg0.3. A small preference for unlike nearest neighbours is observed which diminishes with rising temperature. The volume per atom varies almost linearly with composition. However, the coefficient of thermal expansion, and the other properties which have been measured, show more or less pronounced deviation from linear behaviour. The excess specific heat is larger for the liquid than for the solid phase

A look at membrane patches with a scanning force microscope.

We combined scanning force microscopy with patch-clamp techniques in the same experimental setup and obtained images of excised membrane patches spanning the tip of a glass pipette. These images indicate that cytoskeleton structures are still present in such membrane patches and form a strong connection between the membrane and the glass wall. This gives the membrane patch the appearance of a tent, stabilized by a scaffold of ropes. The lateral resolution of the images depends strongly on the observed structures and can reach values as low as 10 nm on the cytoskeleton elements of a (inside-out) patch. The observations suggest that measurements of membrane elasticity can be made, opening the way for further studies on mechanical properties of cell membranes

Short antisense oligonucleotide-mediated inhibition is strongly dependent on oligo length and concentration but almost independent of location of the target sequence

The inhibitory effect of short antisense oligodeoxynucleotides (aODNs) on cRNA expression in Xenopus oocytes was measured using an electrophysiological assay based on subunit-specific block of cloned alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors. The effect of both phosphorothioate-modified (PS) and phosphodiester (PO) aODNs was strongly length dependent with a half-maximal inhibition calculated for an oligo length of 7.6 nucleotides (nt) and 9.9 nt, respectively. More than 95% inhibition was mediated by a PS aODN of 12 nt and by PO aODNs > or = 15 nt. At a given length PS and PO aODNs showed differential dependence of their inhibitory effect on the injected aODN concentration (half-maximal inhibition at 18 ng/microliter for a PO 12-mer and at 0.19 ng/microliter for a PS 12-mer) and differential saturation behavior. The inhibitory effect of aODNs, even as short as 8 nt for PS oligomers, was highly sequence specific, but almost independent of the position of the respective target site on the cRNA (for PS 8-mers, > or = 70% expression inhibition throughout the tested target sites from the translation initiation to the 3-untranslated region). Thus, short PS aODNs can be reliably used in order to specifically inhibit protein expression in experiments addressing physiological, molecular biological, and perhaps even therapeutical issues