Structural aspects of the association of FcepsilonRI with detergent-resistant membranes

We recently showed that aggregation of the high affinity IgE receptor on mast cells, FcepsilonRI, causes this immunoreceptor to associate rapidly with specialized regions of the plasma membrane, where it is phosphorylated by the tyrosine kinase Lyn. In this study, we further characterize the detergent sensitivity of this association on rat basophilic leukemia-2H3 mast cells, and we compare the capacity of structural variants of FcepsilonRI and other receptors to undergo this association. We show that this interaction is not mediated by the beta subunit of the receptor or the cytoplasmic tail of the gamma subunit, both of which are involved in signaling. Using chimeric receptor constructs, we found that the extracellular segment of the FcepsilonRI alpha subunit was not sufficient to mediate this association, implicating FcepsilonRI alpha and/or gamma transmembrane segments. To determine the specificity of this interaction, we compared the association of several other receptors. Interleukin-1 type I receptors on Chinese hamster ovary cells and alpha4 integrins on rat basophilic leukemia cells showed little or no association with isolated membrane domains, both before and after aggregation on the cells. In contrast, interleukin-2 receptor alpha (Tac) on Chinese hamster ovary cells exhibited aggregation-dependent membrane domain association similar to FcepsilonRI. These results provide insights into the structural basis and selectivity of lipid-mediated interactions between certain transmembrane receptors and detergent-resistant membranes.     

Effect of matrix molecular weight on the dispersion of nanoclay in unmodified high density polyethylene

The effect that polymer molecular weight has on the dispersion of relatively polar montmorillonite (MMT) in nonpolar, unmodified high density polyethylene (HDPE) was examined. Polymer layered silicate (PLS) nanocomposites were prepared via melt compounding in a single screw extruder using three unmodified HDPE matrices of differing molecular weight and organically modified MMT (organoclay) in concentrations ranging from 2 to 8 wt%. The weight average molecular weights (M _W) of the HDPE matrices used ranged from 87,000 to 460,000 g/mol. X‐ray diffraction (XRD), tensile testing, dynamic mechanical thermal analysis (DMTA), and dynamic rheometry were performed on these nanocomposites. Nanocomposites generated from the high molecular weight (HMW) HDPE matrix exhibited increased intercalation of the MMT as shown by XRD and greater improvements in the Young's modulus when compared with nanocomposites generated from the low (LMW) and middle molecular weight (MMW) matrices. DMTA measurements carried out in torsion showed that the increase in shear modulus of the HMW nanocomposites was not as great as that of the LMW and MMW counterparts as observed from a lower percentage enhancement in the storage modulus (G′) and estimated heat distortion temperature (HDT). This was attributed to the higher degree of mechanical anisotropy in the HMW nanocomposites. POLYM. COMPOS., 28:499–511, 2007. © 2007 Society of Plastics Engineers     

Noise performance of separate absorption, grading, charge andmultiplication InP/InGaAs avalanche photodiodes

The noise performance of planar separate absorption, grading, charge and multiplication avalanche photodiodes was investigated at room temperature over a range of integrated charge (2.7-3.3×10¹² cm^-2) and high field InP thickness (0.09-0.62 μm). It is found that the effective k of 0.38 is nearly independent of these parameters. These observations are consistent with ionization both inside and outside the high-field InP region. Furthermore, the temperature dependence was investigated, with the result that k increases slightly from 0.42 to 0.53 with increasing temperature in the range -30 to +85°C     

Teaching by Telephone

The educational telephone network has proved a low cost, effective, and wide-reaching way of meeting the demand for continuing education.     

Absorption of ammonia in a batch bubble column

The batch neutralization of dilute hydrochloric acid by ammonia in a 10.16 cm i.d. bubble column has been examined. Experimental results agree with a diffusion-type mixing model when 5.08 cm disc baffles are present, but agreement is only approximate with 7.62 cm diameter baffles. Axial dispersion coefficients have been determined and compared with published data. A simple batchwise procedure for evaluating bubble columns is suggested.     

Fc epsilon RI-mediated recruitment of p53/56lyn to detergent-resistant membrane domains accompanies cellular signaling

Detergent-resistant plasma membrane structures, such as caveolae, have been implicated in signalling, transport, and vesicle trafficking functions. Using sucrose gradient ultracentrifugation, we have isolated low-density, Triton X-100-insoluble membrane domains from RBL-2H3 mucosal mast cells that contain several markers common to caveolae, including a src-family tyrosine kinase, p53/56lyn. Aggregation of Fc epsilon RI, the high-affinity IgE receptor, causes a significant increase in the amount of p53/56lyn associated with these low-density membrane domains. Under our standard conditions for lysis, IgE-Fc epsilon RI fractionates with the majority of the solubilized proteins, whereas aggregated receptor complexes are found at a higher density in the gradient. Stimulated translocation of p53/56lyn is accompanied by increased tyrosine phosphorylation of several proteins in the low-density membrane domains as well as enhanced in vitro tyrosine kinase activity toward these proteins and an exogenous substrate. With a lower detergent-to-cell ratio during lysis, significant Fc epsilon RI remains associated with these membrane domains, consistent with the ability to coimmunoprecipitate tyrosine kinase activity with Fc epsilon RI under similar lysis conditions [Pribluda, V. S., Pribluda, C. & Metzger, H. (1994) Proc. Natl. Acad. Sci. USA 91, 11246-11250]. These results indicate that specialized membrane domains may be directly involved in the coupling of receptor aggregation to the activation of signaling events.     

Pumping effects due to reciprocating asymmetric baffles

A significant pumping effect at low differential head can be achieved by oscillating one or more asymmetric baffle plates in a tube. The resistance to backflow of fluid relative to the plates is affected by the direction of movement of the plates, for a given plate speed. This effect has been demonstrated in a 5 cm dia. tube, using an air-driven plate assembly at frequencies from 0.5 to 2.25 Hz and strokes from 10 to 25 cm. The forms of the characteristic curves for a given baffle geometry depend on the frequency and stroke of operation. It is concluded that this type of pump could be used for very abrasive or fibrous fluids where the head and delivery rate requirements are relatively low.     

Fluid elasticity measurements from hole pressure error data

A slit die of variable height H (0.135 in., 0.1975 in., or 0.2488 in.) width W 2.5 in., and variable length L_e (12.0 in., 12.5 in., or 13.5 in.) has been designed and constructed for measuring the wall shear stress σ_w and the hole pressure error P_H. Values of P_H and σ_w are obtained directly and rapidly on a chart recorder from three commercial pressure transducers by means of an electronic differencing technique. The reliability of P_H measurements is established by the excellent agreement between viscosity η values obtained from this apparatus and a rheogoniometer and by measuring negligible values of P_H for the New tonian fluid, glycerine, for σ_w < 800 dyn/cm² and values of P_H > 0 for σ_w ≥ 800 dyn/cm² and values of P_H < 0 for a low-elasticity solution of polystyrene in dioctyl phthalate (DOP). Values of P_H are found to be independent of the distance E of the transducers from the die exit and the die height which indicated that P_H is independent of the undisturbed wall pressure P_w for constant values of σ_w. Our values agree well with those measured by Higashitani for a similar Separan solution in a different slit die. Using this new slit die, it is shown the P_H is sensitive to changes in molecular weight (MW) for a series of solutions of polystyrene in DOP and that P_H could be used to monitor continuously the changes in molecular structure which occured during the mechanical degradation of a 2.0% aqueous poly(ethylene oxide) solution. The simple relation between P_H and N₁ (P_H = ?cN₁, where c is a constant) is verified for solutions of polystyrene in DOP and aqueous Separan solutions over a large range of flow conditions (? = 1000 sec^?1). Because c is found to vary slightly with polymer type, concentration, and molecular weight, a method is presented for obtaining N₁ directly from P_H data.