Turnover of Brain Monoamine Oxidase Measured In Vivo by Positron Emission Tomography Using l-[11C]Deprenyl

The distribution of carbon-11-labeled L-deprenyl, an irreversible inhibitor of monoamine oxidase type B (MAO-B), was determined in the baboon brain by positron emission tomography. The irreversible blood-to-brain transfer constant (influx constant, K_i) was measured using a complete metabolite-corrected arterial plasma concentration curve. This influx constant was used as a measure of functional enzyme activity for sequential determinations of MAO-B recovery following a single high dose of unlabeled l -deprenyl. The half-life for turnover of MAO-B was thus determined to be 30 days. Using appropriate irreversible inhibitors, this procedure should be generally useful for determining enzyme turnover rates in any organ in vivo and can be applied to some human studies as well.     

Activation of Dopamine Receptors Does Not Affect Phosphoinositide Turnover in NCB-20 Cells

Dopamine inhibits and serotonin stimulates adenylate cyclase activity in a neuroblastoma X Chinese hamster brain explant cell line (NCB-20). The inhibition of cyclic AMP accumulation by dopamine was blocked by pretreatment of the cells with pertussis toxin. Carbachol and bradykinin stimulated the accumulation of water-soluble inositol phosphates whereas thyrotropin-releasing hormone, vasopressin, neurotensin, and phenylephrine were without effect. Dopamine and serotonin had no significant effect on carbachol-induced phosphoinositide hydrolysis or the levels of the parent lipids within the membrane. Forskolin induced a much larger stimulation of cyclic AMP than did serotonin, and caused an increase in the levels of phosphatidylinositol-4-phosphate and phosphatidyl inositol-4,5-bisphosphate in the cell membrane.     

2-Amino-7-Phosphonoheptanoic Acid Inhibits Insulin-Induced Convulsions and Striatal Aspartate Accumulation in Rats with Frontal Cortical Ablation

Pretreatment of rats with the excitatory amino acid antagonist 2-amino-7-phosphonoheptanoic acid (2-APH; 0.5 mmol/kg, i.p.) protected against insulin-induced clonic seizures. Complete protection was observed in 38% of the rats and partial protection in an additional 50%. Lesioning of the corticostriatal pathway by frontal cortical ablation caused decreases in the striatal levels of aspartate (-28%) and glutamate (-18%), an increase in striatal glutamine level (45%), and decreased high-affinity uptake of D-[3H]aspartate (-27%) in the lesioned dorsal neostriatum. Insulin-induced hypoglycemia caused a predicted sharp increase in aspartate level (165%) and decreased glutamate (-20%) and glutamine (-38%) levels in the intact striatum. Pretreatment of rats with 2-APH significantly reversed the insulin-induced changes in striatal aspartate, glutamate, and glutamine levels, especially in the intact hemisphere. In normoglycemic control rats, the "metabolic," i.e., concentration in the lesioned hemisphere, aspartate pool constituted 72% and the "synaptic," i.e., the concentration difference between the intact and lesioned hemispheres, 28% of the total striatal aspartate pool. 2-APH had no effect on the level of "metabolic" aspartate in the striata of normoglycemic rats but caused an almost complete suppression of "synaptic" aspartate. Following insulin-induced hypoglycemia, the "metabolic" aspartate pool doubled, whereas the "synaptic" aspartate pool increased 3.5-fold in the absence of 2-APH. The insulin-induced rise in "synaptic" aspartate level was almost completely blocked by 2-APH (a 5% rise instead of a 3.5-fold rise).(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

Effect of osmotic stress on protein turnover in Lemna minor fronds

Evidence is presented that although many proteins from the fronds of Lemna minor L. undergo enhanced degradation during osmotic stress, ribulose-1,5-bisphosphate carboxylase (RuBPCase) is not degraded. Instead RuBPCase is converted in a series of steps to a very high-molecular-weight form. The first step involves the induction of an oxidase system which after 24 h of stress converts RuBPCase to an acidic and catalytically inactive form. Subsequently, the oxidised RuBPCase protein is gradually polymerized to a number of very large aggregates (molecular weight of several million).The conversion of RuBPCase to a high-molecular-weight form appears to be correlated with (i) a reduction in the number of-SH residues and (ii) the susceptibility to in-vitro proteolysis. Indeed, the number of-SH groups per RuBPCase molecule decreases from 89 in the native enzyme to 54 and 22 in the oxidised and polymerized forms, respectively. On the other hand, the oxidised enzyme is more susceptible to in-vitro proteolysis than the native form. However, it is the polymerized form of RuBPCase which is particularly susceptible to in-vitro proteolysis.Western-blotting experiments and anti-ubiquitin antibodies were used to detect the presence of ubiquitin conjugates in extracts from osmotically stressed Lemna fronds. The possible involvement of ubiquitin in the formation of the aggregates is discussed.Abbreviations DTT dithiothreitol - EDTA ethylenediamine-tetraacetic acid - FPLC fast protein liquid chromatography - kDa kilodaltons - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulphonyl fluoride - RuBPCase ribulose bisphosphate carboxylase - SDS sodium dodecyl sulphate - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Effects of phorbol esters on endothelial cell microfilaments: Laser scanning confocal microscopy and quantitative morphometry of dose dependent changes

Phorbol esters are known to alter microfilaments but it is not clear if the changes correspond to modulation of the phosphoinositide turnover/protein kinase C system. The novel technique of laser scanning confocal epifluorescence was used to study fiber orientation in phorbol ester treated cells. We treated endothelial cells with control agents and agents known to stimulate protein kinase C: 4 alpha-phorbol, phorbol 12-myristate 13-acetate (PMA), phorbol dibutyrate (PDB), or lipopolysaccharide. After incubation with the test agents, the endothelial cell microfilaments were stained with rhodamine pholloidin and viewed by conventional epifluorescence and by laser scanning confocal epifluorescence microscopy. The images obtained by the confocal microscopy corresponded to a thin optical section through the cells, 300 nm or more in thickness. The microfilaments extended predominantly in the plane of focus. After exposure of the cells to phorbol esters, the stress fibers became more nearly parallel in arrangement or were shortened, but remained in the plane of focus. The modification of microfilaments in response to phorbol esters was quantitated by a single blind analysis. In order to compare the morphological changes with a biochemical action of the phorbol esters, we measured phosphoinositide turnover. The dose-dependence of morphological changes was compared and contrasted to the dose-dependent effect of phorbol esters on bradykinin-stimulated phosphoinositide turnover. PMA had about the same EC50 (1-5 nM) for both biochemical and morphological processes. PDB was less potent in inducing the disruption of microfilament structure than in inhibiting phosphoinositide turnover. Lipopolysaccharide was ineffective in inducing a morphological change under these conditions. A simple activation of protein kinase C is insufficient to explain the dose-dependent effects of phorbol esters. Thus a morphometric analysis can help distinguish the potency of cytoskeleton modulators.     

Relation of phosphatidylinositol metabolism to glycolytic pathway in skeletal muscle membranes

Skeletal muscle triads are possessing the whole set of enzymes of the phosphatidylinositol (PI)-linked signal generating pathway, PI-kinase, PI(4)P-kinase, and PI(4,5)P₂-phospholipase C (PLC). The activities of these enzymes are comparable to those found in other cell types for which a functional role of the PI-pathway in intracellular signal transduction has been established. For skeletal muscle an unequivocal function and an initiating signal for Ins(1,4,5)P₃-liberation is still unknown. However, the observed Ca-dependency of PLC activity suggests that here Ins(1,4,5)P₃ production is a consequence rather than a cause of increasing cytosolic Ca²⁺. Recently, the glycolytic enzyme aldolase, whose activity can be modulated by inositol polyphosphates, has been localized in the triadic structure. The enzyme which has a high affinity to Ins(1,4)P₂, Ins(1,4,5)P₃ and Ins(1,3,4,5)P₄, seems to be compartmentalized to the junctional foot structure from which it is released upon binding of these molecules. This phenomenon could reflect a capability for regulation of the glycolytic flux even for aldolase, especially if a non steady-state situation in the junctional gap is considered. Meanwhile we have accumulated evidence for the operation of a partial glycolytic sequence in the junctional region established by the enzymes aldolase, glyceraldehyde-3-P (GAP) dehydrogenase and phosphoglycerate kinase. This system is able to produce ATP upon oxidation of GAP and could be, because of the inositol polyphosphate-sensing abilities of aldolase, a target for the membrane associated PI-pathway. The ATP production is however transient which indicates the coupling to an ATP hydrolyzing reaction. Thus, it appears that the ATP produced by the membrane associated system is effectively utilized by an ATP consuming membrane localized system like PI-metabolism or protein kinases. There are indications that exogeneously added ATP does not equilibrate with the ATP synthesized in the junctional region which suggests an effective structural or kinetical compartmentalization of this system. Therefore it is hypothesized that the ATP synthesized by the membrane associated glycolytic sequence is utilized in membrane localized reactions.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Effect of CO2 enrichment and nitrogen availability on resource acquisition and resource allocation in a grass,Bromus mollis

Summary The effects of CO₂ enrichment on the growth, biomass partitioning, photosynthetic rates, and leaf nitrogen concentration of a grass, Bromus mollis (C₃), were investigated at a favorable and a low level of nitrogen availability. Despite increases in root: shoot ratios, leaf nitrogen concentrations were decreased under CO₂ enrichment at both nitrogen levels. For the low-nitrogen treatment, this resulted in lower photosynthetic rates measured at 650 l/l for the CO₂-enriched plants, compared to photosynthetic rates measured at 350 l/l for the non-enriched plants. At higher nitrogen availability, photosynthetic rates of plants grown and measured at 650 l/l were greater than photosynthetic rates of the non-enriched plants measured at 350 l/l. Water use efficiency, however, was increased in enriched plants at both nitrogen levels. CO₂ enrichment stimulated vegetative growth at both high and low nitrogen during most of the vegetative growth phase but, at the end of the experiment, total biomass of the high and low CO₂ treatments did not differ for plants grown at low nitrogen availability. While not statistically significant, CO₂ tended to stimulate seed production at high nitrogen and to decrease it at low nitrogen.