The nongenomic membrane receptor-mediated mechanism is an important but not fully explored facet in the action of steroid hormones. In the present study the action of glucocorticoid on nerve cell membrane was studied using isolated and superfused coeliac ganglion preparations by an intracellular electrophysiological technique. Glucocorticoid hyperpolarized the membrane potential of guinea pig ganglion neurons in vitro with a latency of less than 2 min. The effect persisted under low Ca2+/high Mg2+ superfusion conditions and could be abolished by RU38486, a competitive antagonist of glucocorticoid cytosolic receptor. Bovine albumin glucocorticoid conjugant exhibited the same effect. In neurons with spontaneous discharges the glucocorticoid-caused hyperpolarization of membrane potential decreased or eliminated the discharges. The results strongly suggest that glucocorticoid can act nongenomically through its neuronal membrane receptor. The steroid-induced hyperpolarization was accompanied by a change in the input resistance of the cell, indicating an involvement of some kind(s) of ion channel(s) in the action of glucocorticoid.

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N-methyl-D-aspartate (NMDA) receptors play major roles in synaptic transmission and plasticity, as well as excitotoxicity. NMDA receptors are thought to be tetrameric complexes mainly composed of NMDA receptor (NR)1 and NR2 subunits. The NR1 subunits are required for the formation of functional NMDA receptor channels, whereas the NR2 subunits modify channel properties. Biochemical and functional studies indicate that subunits making up NMDA receptors are organized into a dimer of dimers, and the N termini of the subunits are major determinants for receptor assembling. Here we used a biophysical approach, fluorescence resonance energy transfer, to analyze the assembly of intact, functional NMDA receptors in living cells. The results showed that NR1, NR2A, and NR2B subunits could form homodimers when they were expressed alone in HEK293 cells. Subunit homodimers were also found existing in heteromeric NMDA receptors formed between NR1 and NR2 subunits. These findings are consistent with functional NMDA receptors being arranged as a dimer of dimers. In addition, our data indicated that the conformation of NR1 subunit homodimers was affected by the partner NR2 subunits during the formation of heteromeric receptor complexes, which might underlie the mechanism by which NR2 subunits modify NMDA receptor function. N-Methyl-D-aspartate (NMDA)1 receptors are a subtype of the ionotropic glutamate receptors, which also include ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors and kainate receptors. NMDA receptors play critical roles in synaptic plasticity, memory formation, and several types of neurological disorders (1-3). Three gene families, named NR1, NR2, and NR3, encode subunits composing NMDA receptors. The NR1 subunit is encoded by a single gene, which undergoes extensive splicing to yield eight splice variants, NR1-1a and -1b to NR1-4a and -4b. The NR2 subunit exists in four isoforms (NR2A-D) encoded by different but closely related genes (reviewed in Ref.2). All of the subunits have a similar membrane topological structure, with three transmembrane domains plus a loop region, an extracellular N terminus, and an intracellular C terminus. Recently, NMDA receptors were thought to be tetrameric channels, for which the relevant evidence comes from the electrophysiological studies of NMDA and AMPA receptors (4 -6) and the evolutionary link between glutamate receptors and tetrameric K ϩ channels (7, 8). The NR1 subunit contains a glycine-binding site (9, 10) and is essential for the formation of functional NMDA receptor channels, whereas the NR2 subunit provides a glutamate-binding site (11, 12) and modifies channel properties, such as current kinetics and channel conductance (13-15). The NR3 subunit does not form a functional NMDA receptor alone, but it can co-assemble with NR1/NR2 complexes to modulate the activity of the NMDA receptor (16 -18).Previous studies have shown that NMDA receptor complexes may contain different NR1 splice variants (19,20) or different NR2 subunits (21-24). Several distinct NMD...

Electrospinning is a recently explored simple and versatile fabrication technique for producing nano-to microscale fibers. The electrospun fiber mats possess a number of characteristics such as high specific surface area, high aspect ratio, and high porosity as a result of random deposition of the fibers, which allow a wide range of potential applications such as optoelectronics, sensor technology, catalysis, filtration, and medicine. 1,2 The mechanical properties of the electrospun fibers or mats are usually different from those of the corresponding bulk materials. Sometimes, the difference is enormous and surprising. [3][4][5] For example, Gu et al. 4 reported a Young's modulus of 50 GPa for polyacrylonitrile single nanofibers, which is much greater than that of the corresponding cast film (1.2 GPa). Kim et al. 5 observed the phenomenon of "necking" with poly(methyl methacrylate) (PMMA)/montmorillonite nanocomposite electrospun single fibers, whereas PMMA is known as a brittle plastic.Polyoxymethylene (POM) is a versatile engineering plastic. 6,7 It is widely used in automobile and electronic industries due to good properties such as good strength, stiffness, abrasion, and chemical resistance. 8,9 Although almost 100 polymer solutions or melts have been electrospun into fibers, 4 to the best of our knowledge, electrospinning of POM has not yet been reported due to presumably poor solubility in common solvents. However, POM is soluble in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is frequently used in electrospinning of natural biopolymers such as collagen and chitin. [10][11][12][13] In this work, electrospinning of POM solutions in HFIP is investigated, and to our surprise, a very high elongation to break was observed with the POM electrospun fiber mats. Figure 1 shows the morphology of the electrospun POM mat obtained from a 5 wt % solution at 30°C with a relative humidity of 40%. The average diameter is 940 nm, and microporous structure was observed with an average pore size of 150 nm. It is well-known that microporous structure is frequently obtained when volatile solvents are used for electrospinning, 14,15 and that high relative humidity also favors formation of pores. 1,16 HFIP is a volatile solvent with a boiling point of 58°C. The formation of microporous structure in the current case is understandable, although the electrospun fibers of biopolymers reported so far have no obvious pores. [10][11][12][13] The mechanical properties of the nonwoven POM electrospun mats were measured by tensile tests after thorough drying at 40°C under vacuum, and a typical load-elongation curve is shown in Figure 2a. Elongation of 460% was observed. For comparison, the elongation at break of bulk POM such as a tensile bar obtained from injection molding is known to be 40-50%, 9 and that of the thin film cast from the same solution used for electrospinning is only 1%. Therefore, the elongation at break of the electrospun nonwoven mat is about 10-fold of that of the bulk tensile bar and about 460-fold of that of the...