Calcium- Versus G Protein-Mediated Phosphoinositide Hydrolysis in Rat Cerebral Cortical Synaptoneurosomes

The role of calcium and sodium in stimulating phosphoinositide hydrolysis in brain was investigated in rat cerebral cortical synaptoneurosomes. In buffer containing 136 mM sodium and various concentrations of added calcium (0-1.0 mM), basal, potassium-stimulated, and norepinephrine-stimulated formation of 3H-inositol phosphates decreased with decreasing extracellular calcium. Potassium- and norepinephrine-stimulated formation of 3H-inositol phosphates was reduced to basal levels by addition of EGTA. Isosmotically replacing sodium with choline chloride or N-methyl-D-glucamine to disrupt Na+/Ca2+ exchange resulted in a large increase in the formation of 3H-inositol phosphates. Measurement of cytosolic calcium with fura-2 revealed that the cytosolic calcium concentration was sensitive to changes in the extracellular calcium concentration and increased on resuspension of synaptoneurosomes in sodium-free rather than sodium-containing medium. In the absence of sodium, potassium-stimulated formation of 3H-inositol phosphates was reduced or eliminated, depending on the extracellular calcium concentration. Subtraction of basal formation of 3H-inositol phosphates from that in the presence of 1 mM carbachol or 100 microM norepinephrine revealed that the carbachol-stimulated component was the same in the presence and absence of sodium, whereas the norepinephrine-stimulated component was reduced in the absence of sodium. Addition of the protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate inhibited norepinephrine- and, to a lesser extent, carbachol but not basal or aluminum fluoride-stimulated formation of 3H-inositol phosphates in sodium-free medium. These results suggest that an increase in intracellular calcium, via disruption of Na+/Ca2+ exchange or depolarization-induced calcium influx, may explain previous demonstrations that agents that stimulate Na+ influx can also stimulate phosphoinositide hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Using Molecular Dynamics to Predict Factors Affecting Binding Strength and Magnetic Relaxivity of MRI Contrast Agents

We demonstrate the use of molecular dynamics and molecular mechanics methods to calculate properties and behavior of metal-chelate complexes that can be used as MRI contrast agents. Static and dynamic properties of several known agents were calculated and compared with experiment. We calculated the static properties such as the q-values (number of inner shell waters) and binding distances of chelate atoms to the metal ion for a set of chelates with known X-ray structure. The dynamic flexibility of the chelate arms was also calculated. These computations were extended to a series of exploratory chelate structures in order to estimate their potential as MRI contrast agents. We have also calculated for the first time the NMR relaxivity of an MRI contrast agent using a long (5 nsec) molecular dynamics simulation. Our predictions are promising enough that the method should prove useful for evaluating novel candidate compounds before they are synthesized. One novel static property, the projected area of chelate atoms onto a virtual surface centered on the metal ion (gnomonic projection), was found to give an effective measure of how well the chelate atoms use the free space around the metal ion.     

Two individuals with elliptocytic red cells apparently lack three minor erythrocyte membrane sialoglycoproteins.

We have studied the erythrocytes of two individuals (P. L. and K. W.) who lack the Gerbich (Ge) blood-group antigen. The erythrocytes of P. L. and K. W. were not reactive with two monoclonal antibodies (NBTS/BRIC 4 and NBTS/BRIC 10) which reacted with normal erythrocytes. The membranes of P. L. and K. W. erythrocytes appeared to lack three minor sialoglycoproteins (beta, beta 1 and gamma). These three minor sialoglycoproteins were found to be associated with the cytoskeletons of normal erythrocytes. Approx. 10% of the erythrocytes of P. L. and K. W. were frankly elliptocytic. We suggest that one or more of the minor sialoglycoproteins may play a part in maintaining the discoid shape of the human erythrocyte.     

Evidence for the influence of seagrasses on the benthic nitrogen cycle in a coastal plain estuary near Beaufort,North Carolina (USA)

A study was undertaken to evaluate the interrelationship between the presence of seagrasses, Zostera marina and Halodule wrightii, and the physical and chemical properties of sediments in a coastal plain estuary near Beaufort, North Carolina. In sediments underlying a cover of seagrass, silt-clay, organic matter, exchangeable ammonium, ammonium dissolved in pore waters and total nitrogen were larger than in unvegetated profiles. The magnitude of the physical and chemical properties of sediments varied according to the location of the station in relation to the vegetation, as well as the continuity in the distribution of the seagrass. The largest pools of nitrogen, the finest sediment texture, and the greatest organic matter content were in sediments associated with the mid bed regions of seagrass meadows, intermediate at the edges of the bed and small isolated patches of grass, and least in unvegetated substrate.General conclusions from this study are: 1) once established, seagrasses appear capable of modifying the sediment texture as well as the organic matter and nitrogen content; 2) nitrogen accumulates beneath the vegetation suggesting that vegetated sediments are sinks; however, functional recycling mechanisms seem to be operating as suggested by the larger magnitude of remineralized nitrogen in the vegetated profiles; and 3) the establishment of seagrasses in this geographical region are not necessarily restricted by the sediment properties measured in this study. These data and conclusions are discussed in regard to an application of contemporary theories of ecosystem development to seagrass systems.Contribution Number 82-22-B     

Pretreatment of cellulosic wastes to increase enzyme reactivity

The enzymatic hydrolysis of cellulose to glucose is generally a slow reaction. Different pretreatments, such as ball milling to a ?200 mesh or swelling in 1–2% NaOH are reported to increase the reactivity considerably. In this work a fiber fraction from cattle manure was treated in an autoclave for 5–30 min at temperatures ranging from 130–200°C. The reactivity of the cellulose, measured by incubating samples with a commercial cellulase preparation for one hour at 50°C and pH 4.8, was increased by a factor of 4–6 compared to NaOH treatment and 10–12 compared to untreated fiber. The increased reaction rate is probably mostly due to an increase in cellulose availability to enzymatic attack, as structural hemicellulose is hydrolyzed and removed during the treatment. Sugars, produced by hemicellulosis, hydrolysis, will react further to give caramelization products. These side reactions were shown to be suppressed by short treatment times. The treated fiber could support growth of a mixed culture of Trichoderma viride and Candida utilis only after washing, indicating the formation of water soluble inhibitory products during treatment. The treatment with high-temperature steam can probably be used also with other cellulosic materials to increase reactivity. This may be an attractive way to prepare low-valued wastes such as manure fibers, straw, stalks, or corn cobs for fermentation processes to increase the protein content or for use directly as ruminant animal feed.     

Bait traps remain attractive to euglossine bees even after two weeks: a report from Brazilian Atlantic forest

Bait traps are effective and commonly used method in the studies of orchid bees. Important questions in the context of this method, including those related to bait dispersion, how long baits remain attractive, the distance from which males are supposed to be attracted to lures and so on, are still open subjects. Data on the attractiveness of bait traps that have remained in the field during two weeks in a large Atlantic forest preserve are presented. Four main results emerge from the data: (i) the abundance of specimens collected per day decreased in all the attractants as the traps were left on the field; (ii) despite this decrease, the absolute number of individuals collected after eight and fifteen days is remarkably, mostly in eugenol and vanillin baits; (iii) the vast majority of species, 22 of 25, was already collected on the first sample day; (iv) a consistent variation in the relative abundance of individuals collected in each scent as collections were made. We urge that bait traps should not be left in the field beyond what is strictly necessary since there is a real possibility of collecting a significant number of individuals as these traps remain available.     

Mini-review: discovery and development of platinum complexes designed to circumvent cisplatin resistance

The discovery and development of new platinum-containing anticancer drugs have represented an integral part of anticancer drug development at the Institute of Cancer Research, Sutton, over almost 20 years. As part of a collaboration with chemists at Johnson Matthey, later AnorMED, four major new classes of platinum drug have been discovered, three of which have entered clinical trial. Earlier studies led to the clinical development of the less toxic analogue carboplatin and JM216, the first orally administerable platinum drug. In recent years, the focus has been on two lead complexes designed to overcome the major mechanisms of tumour resistance to cisplatin: JM335 (trans-ammine (cyclohexylaminedichlorodihydroxo) platinum(IV)), an active trans platinum complex; and ZD0473 (cis-amminedichloro(2-methylpyridine) platinum(II)), a sterically hindered complex shown to be less reactive towards thiol-containing molecules than cisplatin. JM335 shows some circumvention of acquired cisplatin resistance in vitro and exhibits unique cellular pharmacological properties in comparison to cisplatin or its cis-isomer in terms gene-specific repair of adducts on DNA and the rate of induction of apoptosis. ZD0473 is now in phase I clinical trial. Myelosuppression is the dose-limiting toxicity at a dose of 130 mg/m2 given i.v. every 3 weeks and there has been evidence of antitumour activity. ZD0473-resistant human ovarian carcinoma cell lines have been established in vitro. Some mechanisms of resistance common to those described for cisplatin (decreased drug uptake, increased glutathione) have been observed plus, in one cell line, increased BCL2 levels and loss of the DNA mismatch repair protein MLH1.