Cysteamine-induced reduction in gastrointestinal somatostatin: evidence for a region-specific loss in immunoreactivity

Administration of cysteamine (beta-mercaptoethylamine; 2-aminoethanethiol) to rats has been shown to decrease the levels of somatostatin-like immunoreactivity (SLI) in the gastrointestinal tract and pancreas but its mode of action is unclear. In the current study the effect of cysteamine on gastrointestinal and pancreatic SLI has been studied using two antisera with different regional specificities. In addition, the in vitro effect of cysteamine on SS-14 and SS-28 has been studied by high-performance liquid chromatography (HPLC). Characterization of the two antisera (AS 26.3.2 and AS 1001) with a range of analogs of SS-14 revealed that both were directed against the midportion of the molecule but that AS 1001 was also sensitive to changes at the N- and C-termini. Tissue extracts from cysteamine-treated rats measured with AS 26.3.2 showed no significant change for the stomach, jejunum or pancreas but duodenal levels were reduced. With AS 1001 SLI levels were reduced in all tissues. Gel permeation chromatography of stomach extracts measured with AS 1001 showed a reduction in both SS-14 and SS-28. With AS 26.3.2 an increase in SLI eluting prior to the SS-14 peak occurred explaining why no significant reduction in total SLI was detected. With duodenal extracts the elution profiles with AS 1001 reflected the large reduction in total SLI whereas with AS 26.3.2 a smaller reduction occurred. Both SS-14 and SS-28 were reduced. HPLC analysis of SS-14 and SS-28 following incubation with cysteamine in vitro showed a time-dependent decrease in both somatostatin species with absorbance at 280 nm was measured. New peptide peaks which developed were not all detectable by radioimmunoassay with either antibody. The results suggest that cysteamine causes a change in the structure of somatostatin which probably first involves a reduction of the disulphide bridge and then the N- and C-terminal regions of the molecule thus making it unmeasurable by antisera sensitive to changes in these regions.     

Steric repulsion between phosphatidylcholine bilayers

The change in pressure needed to bring egg phosphatidylcholine bilayers into contact from their equilibrium separation in excess water has been determined as a function of both distance between the bilayers and water content. A distinct upward break in the pressure-distance relation appears at an interbilayer separation of about 5 A, whereas no such deviation is present in the pressure-water content relation. Thus, this break is not a property of the dehydration process per se, but instead is attributed to steric repulsion between the mobile lipid head groups that extend 2-3 A into the fluid space between bilayers. That is, electron density profiles of these bilayers indicate that the observed break in the pressure-spacing relation occurs at a bilayer separation where extended head groups from apposing bilayers come into steric hindrance. The pressure-spacing data are used to separate steric pressure from the repulsive hydration pressure, as well as to quantitate the range and magnitude of the steric interaction. An appreciable fraction of the measured steric energy can be ascribed to a decrease in configurational entropy due to restricted head-group motion as adjacent bilayers come together.     

The establishment of heliothine cell lines and their susceptibility to two baculoviruses

Summary A total of eight cell lines were established from Helicoverpa armigera (3) and H. punctigera (5) embryos and ovaries. Cell lines were established and grown in TC100 and/or TC199-MK containing 10% fetal bovine serum. The serum-free medium ExCell™ 400 was also used, with and without 10% supplemental fetal bovine serum, but failed to generate cell lines from fat bodies, embryos, or ovarian tissues. Cell lines consisted of heterogenous cell types ranging from oval to fibroblast-like. This is the first report on the successful establishment of cell lines from H. punctigera. Cell lines from the two species were distinguishable from each other by DAF-PCR, and noticeable differences in minor bands were observed among cell lines from the same species. All of the established cell lines from both species were susceptible to HzSNPV but did not replicate more virus than that of a H. zea cell line (BCIRL-HZ-AM1-A11). However, an H. punctigera cell line (HP1) replicated AcMNPV to the highest titer (1.0×10⁸ 50% tissue culture infective dose/ml), and only one of the H. armigera cell lines (HA1) was susceptible to this virus.     

Habitat size influences food web structure in drying streams

Biodiversity in running waters is threatened by an increased severity and incidence of low‐flow extremes resulting from global climate change and a growing human demand for freshwater resources. Although it is unknown how and to what extent riverine communities will change in the face of these threats, considerable insight will be gained from efforts aimed at quantifying habitat size‐related controls on the trophic relationships among taxa in streams experiencing extreme flow loss. Here we report on a detailed space‐for‐time survey of replicate stream food webs sampled along the perennial‐ to‐drying continuum in each of fourteen different intermittent South Island, New Zealand streams. We quantified several structural attributes of food webs at fifty‐eight sites, including two taxonomically‐based metrics (web size, predator:prey ratio) and three stable isotope‐based metrics (food chain length [FCL], trophic area, δ¹³C range); we also quantified habitat size‐, disturbance‐, and resource‐related covariates at each site. Food web structure varied widely across sample sites within and across study streams and much of this variation was explained by habitat size. Consistent with our predictions, we found that food webs became smaller (ca 30 to ca 15 taxa, ca 20‐fold reduction in stable isotope‐based trophic area) and shorter (maximum trophic position [FCL] from 4.1 to 2.0, 25% reduction in predator:prey ratio) as we moved from the largest to smaller habitats. These results, and a comparison of our findings with those from a similar assessment conducted in perennial streams, suggest that there are perturbation thresholds which may trigger food web collapse when exceeded, and further imply that food webs may ultimately be ‘sized’ to minimum flows rather than average flow conditions. Our work provides a basis for making general predictions about how habitat contraction, and flow loss in particular, may affect communities and additionally provides insight on mechanisms warranting further attention.     

Cortical network dynamics with time delays reveals functional connectivity in the resting brain

In absence of all goal-directed behavior, a characteristic network of cortical regions involving prefrontal and cingulate cortices consistently shows temporally coherent fluctuations. The origin of these fluctuations is unknown, but has been hypothesized to be of stochastic nature. In the present paper we test the hypothesis that time delays in the network dynamics play a crucial role in the generation of these fluctuations. By tuning the propagation velocity in a network based on primate connectivity, we scale the time delays and demonstrate the emergence of the resting state networks for biophysically realistic parameters.     

The solution structure and interactions of CheW from Thermotoga maritima.

Using protein from the hyperthermophile Thermotoga maritima, we have determined the solution structure of CheW, an essential component in the formation of the bacterial chemotaxis signaling complex. The overall fold is similar to the regulatory domain of the chemotaxis kinase CheA. In addition, interactions of CheW with CheA were monitored by nuclear magnetic resonance (NMR) techniques. The chemical shift perturbation data show the probable contacts that CheW makes with CheA. In combination with previous genetic data, the structure also suggests a possible binding site for the chemotaxis receptor. These results provide a structural basis for a model in which CheW acts as a molecular bridge between CheA and the cytoplasmic tails of the receptor.     

Images of divalent cations in unstained symmetric and asymmetric lipid bilayers

Divalent cations have been microscopically visualized in association with simple lipid bilayers. Symmetric and asymmetric oriented bilayers were constructed from fatty acid monolayers and were cut in thin transverse sections for examination by bright field electron microscopy in the absence of stains, fixatives or embedding materials. It has been found that bilayers formed of lipid molecules having alkaline earth head groups exhibit natural electron contrast. The intrinsic image has been linked to local variations in the bilayer absolute electron density profile determined by X-ray diffraction analysis of the same specimens (McIntosh, T.J., Waldbillig, R. C. and Robertson J. D. (1976) Biochim. Biophys. Acta 448, 15–33). By combining the microscopic, chemical and X-ray evidence it has been estimated that local increments of about 1 g/cm³ can produce detectable electron contrast in 500 Å transverse sections of bilayers.     

Fluorescence depolarization studies of conformation changes in pyrene-butyryl–fumarase

Measurements of fluorescence depolarization on fumarase labeled with the dye pyrene-butyryl were used to test for previously reported structural changes in this enzymes. These apparent conformation changes were of interest because they seemed to correlate with variation in catalytic activity provoked by changing temperature or pH, or by the presence of a competitive inhibitor. In the present studies, the bound dye pyrene-butyryl and the enzymes were investigated systematically to ensure that simple interpretation of fluorescence depolarization results would be meaningful. This analysis showed that carefully controlled experimental condition were necessary to eliminate a dye component with a short fluorescence lifetime and that it was essential to allow for small variations of lifetime with temperature. Contrary to the previous report, a constant rotational relaxation time of the magnitude expected for a nearly spherical molecule of fumarase was found. No changes were detectable by fluorescence depolarization in the size or shape of pyrene-butyryl–fumarase under the solution conditions tested that caused variation in enzyme activity.