Low-noise amplification of voltage and current fluctuations arising in epithelia

Two low-noise differential input amplifiers designed for voltage and current fluctuation measurements in epithelia are described. The first one uses a matched pair of low-noise transistors and is particularly suited for low-frequency current and voltage noise measurements in frog skin and other preparations with impedances below 1 kOmega. The second one is designed around a matched pair of JFETs and can also be used for higher source impedance. Performance is demonstrated with Na(+) current power density spectra obtained from frog skin with the transistor-input stage.     

Accurate high-speed liquid handling of very small biological samples

An assay using reversed-phase high-performance liquid chromatography with ultraviolet detection, at 278 nm, was developed to measure diclofenac in human plasma and urine at concentrations suitable for biopharmaceutical studies. Indomethacin was used as internal standard and separation was performed at 40 degrees C on a C18 Spherisorb column with acetonitrile-0.1 M sodium acetate (35:65, v/v) (pH 6.3) as mobile phase. The sample preparation is simple and rapid (extractionless), and the total run time is less than 5 min. The retention time is 2.8 min for diclofenac and 3.6 min for indomethacin. The detection limit is 0.2 microgram/ml using a 20-microliters loop.     

Pyrolysis of poly(methyl methacrylate co ethyl acrylate)

An investigation of the behavior of poly(methyl methacrylate co ethyl acrylate) with a commercially available filament-type pyrolysis unit and gas chromatogaph was conducted. It has been hypothesized that the quantity of ethyl acrylate monomer produced under the conditions of the experiment is dependent upon the number of ethyl acrylate–methyl methacrylate bonds contained in the copolymer. These observations were made possible by a standardized samples-handling technique in which a uniformsize disk was pyrolyzed at a maximum pyrolysis temperature of 600°C. This enabled reproducible pyrolysis gas chromatograms to be obtained and permitted pyrolysis products of copolymers containing different ratios of ethyl acrylate and methyl methacrylate to be compared. An examination of sequence distribution data, obtained with the aid of a sequence distribution program for copolymers, showed sufficient agreement with the pyrolysis data to support the hypothesis. It has been demonstrated that pyrolysis gas chromatography may be applied to experimentally determine the sequence distribution of copolymers.     

The CD40 TRAF family member interacting motif carries the information to rescue WEHI 231 cells from anti-IGM-induced growth arrest

Engagement of the antigen receptor on WEHI 231 murine B lymphoma cells leads to growth arrest and induction of apoptosis. Concomitant signaling through CD40 sustains proliferation and rescues the cells from apoptosis. At the molecular level, CD40 has been shown to activate nuclear factor kappaB (NF-kappaB) and stress-activated protein kinase (SAPK). The aim of our present study was to define the stretch of the CD40 cytoplasmic tail responsible for mediating these effects in WEHI 231 cells. Using recombinant retroviruses with the enhanced green fluorescent protein as selection marker we transduced WEHI 231 cells with chimeric molecules consisting of the extracellular and transmembrane region of human CD40 or rat CD4 and selected portions of the murine CD40 tail. Chimeric molecules with cytoplasmic fragments encompassing the "CD40 tumor necrosis factor-associated factor family member interacting motif" (TIM) were able to sustain growth and to uphold NF-kappaB activity as efficiently as the whole intracellular region of CD40. While the potential of the motif relative to the whole cytoplasmic tail was independent of the heterologous part of the chimeras it was strongly influenced by its distance to the membrane. Placing the 17-amino acid stretch of the motif too close to the membrane, i. e. only two or four amino acids apart, destroyed its capacity to mitigate the anti-IgM effect. Activation of SAPK through the chimeric molecules always correlated with their ability to activate NF-kappaB activity and to rescue the cells from apoptosis induced by antigen receptor ligation. Our data indicate that CD40-TIM carries most if not all of the information needed to deliver the signals responsible for sustaining growth in anti-IgM-stimulated WEHI 231 cells.     

Effects of WB4101 and chloroethylclonidine on the positive and negative inotropic actions of phenylephrine in rat cardiac muscle

This study was designed to determine if the positive and negative inotropic actions of alpha-1-adrenergic agonists in rat atrial and ventricular myocardium are mediated via different alpha-1-adrenergic receptor (AR) subtypes. Inotropic effects of phenylephrine were examined in isolated left atrial and papillary muscle before and after treatment with prazosin, WB4101 (N-[2-(2,6-dimethoxyphenoxy)ethyl]-2,3-dihydro-1,4-benzodioxin+ ++-2-methanamine), chloroethylclonidine (CEC) and WB4101 plus CEC. Phenylephrine (10 microM) elicited a monophasic positive inotropic response in left atrial muscle and a triphasic inotropic action in papillary muscle (transient positive, then negative inotropic components preceding a sustained positive inotropic response). CEC, WB4101 and prazosin each antagonized the monophasic response in isolated left atria and the sustained positive inotropic response in papillary muscle. CEC and prazosin each antagonized the transient negative inotropic component in papillary muscle. The transient positive inotropic response was not affected by CEC, WB4101 or CEC plus WB4101, but was antagonized by higher concentrations of prazosin. These data suggest that the sustained positive inotropic effect of alpha-1-adrenergic agonists in rat atrial and ventricular myocardium results from stimulation of alpha-1A and alpha-1B ARs, whereas the transient negative inotropic component of the triphasic response in ventricular preparations is mediated via alpha-1B ARs. However, present data do not exclude the possibility that the CEC-sensitive inotropic responses elicited by phenylephrine may be mediated in part by other recently described alpha-1 subtypes. The receptors involved in the transient positive inotropic action cannot be identified by current results.     

Physical chemical properties of solutions of bis-quaternary ammonium bromides

The physical chemical properties of a series of bisalkyldimethyldi-ammonium polyoxyethylene bromides were studied by measuring the critical micelle concentrations as function of their molecular structure. The conductivity vs. concentration plots revealed the existence of two distinct discontinuities which were labeled CMC1 and CMC2. The CMC1 was always lower than the CMC2. The conventional surface tension vs. log concentration curve showed the classical sharp break which coincided with either the CMC1 or the CMC2, but failed to reveal the presence of both critical micelle concentrations in the same experiment. The existence of two CMC2 was attributed to the presence of the two charges localized in separated atoms. The CMC1 and CMC2 appear to follow an expression of the type CMC=A —Bn, where A and B are constants and n the number of carbon atoms present in the hydrocarbon long chain attached to the quaternary ammonium nitrogen. The CMCs appear to increase with the increasing number of oxyethylene residues up to a certain length of the polyoxyethylene chain. For most compounds there was a substantial drop in surface tension with the increasing concentration of the salt. However, some compounds containing only one oxyethylene residue showed practically no surface tension dependence on concentration although the critical micelle concentrations were apparent in the conductivity vs. concentration curve. The energy to transfer one methylene group from the aqueous to the micellar phase was found to vary from −0.57 kT to −0.84 kT. The alkylene oxylated bisquaternary bromides studied appear to have unusual physical chemical properties.     

Male Pheromones Influence the Mating Behavior of <Emphasis Type="Italic">Echinothrips americanus</Emphasis>

Two dibasic esters, the dimethyl ester of hexanedioic acid (dimethyl adipate, DBE-6) and the dimethyl ester of pentanedioic acid (dimethyl glutarate, DBE-5) were found in head-thorax extracts of male Echinothrips americanus. DBE-5 induced abdomen wagging and raising in males and females, which is typically exhibited when encountering a male. DBE-6 was avoided by males and was detected on mated, but not on virgin, females. Both substances applied to virgin females lead to females being ignored by males. The role of both substances is discussed with regard to the male mating system.     

A METHOD FOR TESTING THE CROSS-BENDING STRENGTH OF ENAMELS1

Methods which have been proposed for measuring the strength of enamels, by means of impact tests, are not entirely applicable to enameled flat ware, where the ordinary strains are due to bending of the sheets. An apparatus has been devised by means of which bending stresses can be applied in gradually increasing increments so that the normal behavior of enamels under such stresses can be observed and measured.