Trophic changes,without changes in the external nutrient loading

The impact of the fish population on trophic properties of lake water, was experimentally studied in an oligotrophic Swedish forest lake. Biotic changes following fish removal resulted in a development in oligotrophic direction as shown by the drop in limnetic primary production, pH, total phosphorus, total nitrogen and the increased transparency.     

Formation of thromboxane B2 and hydroxyarachidonic acids in purified human lymphocytes in the presence and absence of PHA.

The metabolism of exogenous and endogenous [14C] arachidonc acid was studied in purified human peripheral blood lymphocytes carefully freed of contaminating platelets. Formation of products co-migrating in a number of different solvent systems with 5-hydroxyarachidonic acid (5-HETE), thromboxane B2 (TB2), prostaglandins and probably 12-hydroxyarachidonic acid (12-HETE) was demonstrated. In cells prelabeled with [14C] arachidonic acid, phytohemagglutinin (PHA) produced substantial (3.5- to 12-fold) increases in 5-HETE, 12-HETE, and TB2 radiolabeling. The metabolism of exogenous [14C] arachidonic acid was much less affected by PHA. Since PHA releases cell-bound arachidonic acid, it appears that the response involving endogenous label is due to increased availability of free arachidonic acid rather than induction of arachidonic acid-metabolizing enzymes. Various inhibitors of arachidonic acid metabolism exerted similar effects in lymphocytes to those described previously in other tissues providing a possible basis for interpreting their inhibitory effects on mitogenesis, described in the preceding paper.     

Interaction of chemotactic factors with human macrophages: induction of transmembrane potential changes

The electrophysiology of chemotactic factor interaction with cultured human macrophages was investigated with standard intracellular recording techniques. In initial studies, E. coli endotoxin-activated serum, added to cell cultures during intracellular recordings, caused membrane hyperpolarizations which were greater than 30 s in duration, 10-50 mV in amplitude, and associated with decreased membrane resistance. Control serum produced smaller hyperpolarizations lasting 10-20 s and 5-30 m V in amplitude. Endotoxin-activated human serum deficient in the third complement component (C3) did not produce hyperpolarizations unless the serum was reconstituted with C3 before activation. Fractionation of normal activated serum by molecular seive chromatography (G-75 Sephadex) indicated that only fractions that eluted with an estimated molecular weight of 12,500 produced membrane potential changes. The active material that was chemotactic for the macrophages was identified as the small molecular weight cleavage product of C5, C5a, by heat stability (30 min at 56 degrees C) and inactivation by goat antisera to human C5 but not C3. 17 percent of macrophages stimulated with C5a exhibited a biphasic response characterized by a small (2-6 mV), brief (1-10 s) depolarization associated with a decreased membrane resistance preceding the larger and prolonged hyperpolarizations. Magnesium-ethylene glycol bis[β-aminoethyl ether]N,N'-tetraacetic acid (Mg [2.5 mM]-EGTA [5.0 mM]) blocked the C5a-evoked potential changes, whereas colchine (10(- 6)M) and cytochalasin B (3.0 μg/ml did not. Hydrocortisone sodium succinate (0.5 mg/ml) decreased the percentage of cells responding to C5a. In related studies, synthetic N-formyl methionyl peptide (f-met-leu-phe), which had chemotactic activity for cultured macrophages, produced similar membrane potential changes. Repeated exposure of macrophages to C5a or f- met-leu-phe resulted in desensitization to the same stimulus. Simultaneous photomicroscope and intracellular recording studies during macrophage stimulation with chemotactic factor demonstrated that the membrane potential changes preceded membrane spreading, ruffling, and pseudopod formation. These observations demonstrate that ion fluxes associated with membrane potential changes are early events in macrophage activation by chemotactic factors     

Beta-cell-targeted overexpression of phosphodiesterase 3B in mice causes impaired insulin secretion, glucose intolerance, and deranged islet morphology

The second messenger cAMP mediates potentiation of glucose-stimulated insulin release. Use of inhibitors of cAMP-hydrolyzing phosphodiesterase (PDE) 3 and overexpression of PDE3B in vitro have demonstrated a regulatory role for this enzyme in insulin secretion. In this work, the physiological significance of PDE3B-mediated degradation of cAMP for the regulation of insulin secretion in vivo and glucose homeostasis was investigated in transgenic mice overexpressing PDE3B in pancreatic beta-cells. A 2-fold overexpression of PDE3B protein and activity blunted the insulin response to intravenous glucose, resulting in reduced glucose disposal. The effects were "dose"-dependent because mice overexpressing PDE3B 7-fold failed to increase insulin in response to glucose and hence exhibited pronounced glucose intolerance. Also, the insulin secretory response to intravenous glucagon-like peptide 1 was reduced in vivo. Similarly, islets stimulated in vitro exhibited reduced insulin secretory capacity in response to glucose and glucagon-like peptide 1. Perifusion experiments revealed that the reduction specifically affected the first phase of glucose-stimulated insulin secretion. Furthermore, morphological examinations demonstrated deranged islet cytoarchitecture. In conclusion, these results are consistent with an essential role for PDE3B in cAMP-mediated regulation of insulin release and glucose homeostasis.     

Morphological Constraints of Shoot Demography of a Clonal Plant: Extra- and Intravaginal Tillers of Festuca rubra

Abstract Festuca rubra forms tillers in two different ways: extravaginally and intravaginally. Demography of these two tiller types was observed in seventeen selected tussocks of Festuca rubra s.s. over four growing seasons. Extravaginal tillers were bigger at birth and on the average produced twice as many daughter tillers per tiller. In general, the natality and mortality of extravaginal tillers were less regular than that of intravaginal tillers. Overall tillering rate per tiller was correlated with the density of the surrounding vegetation; mortality, natality and tiller life span were not. High density of the surrounding vegetation did not result in increased formation of extravaginal tillers. The proportion of the extravaginal tillers was not correlated with the density of the F. rubra tussocks. There is no evidence for foraging by extravaginal tillers, but they do act as founders of small clusters of tillers.     

Tissue differences in vascular permeability induced by leukortriene B4 and prostaglandin E2 in the rat

The activity of synthetic LTB₄ and PGE₂, in increasing vascular permeability was tested simultaneously in seventeen different organs in the rat. Rats were injected in the aortic arch through a cannula in the carotid artery with ¹²⁵-I-albumin, ⁵¹Cr-erythrocytes, and ⁵⁷Co-EDTA. The rats were then injected through the carotid artery cannula with LTB₄, PGE₂ or a combination of LTB₄ and PGE₂. Eight minutes later the rats were killed and the activity of ¹²⁵I, ⁵¹Cr, and ⁵⁷Co measured in different organs. Changes in vascular permeability were infered from changes in the ratios of the isotope activities. LTB₄ (15 μg/kg) induced enhanced permeability in caecum, small bowel, skin, fat pad, stomach, pancreas, and aorta, but not in the heart, brain, colon, testes, diaphragm, forelimb, cremaster muscle, lung, kidney or eye. A lower dose of LTB₄, 3 μg/kg, enhanced vascular permeability in caecum, small bowel, skin, stomach, and aorta. PGE₂ (1 μg/kg) enhanced vascular permeability only in the caecum. A combination of LTB₄ (3 μg/kg) and PGE₂ (1 μg/kg) was more potent than either alone. Rats depleted of neutrophils with anti-neutrophil serum were less sensitive to LTB₄ than intact rats. These findings suggest that the vasculatures of different tissues in the rat vary markedly in their susceptibility to LTB₄ induced increases in permeability.     

Drift Diving by Hooded Seals (Cystophora cristata) in the Northwest Atlantic Ocean

Many pinniped species perform a specific dive type, referred to as a ‘drift dive’, where they drift passively through the water column. This dive type has been suggested to function as a resting/sleeping or food processing dive, and can be used as an indication of feeding success by calculating the daily change in vertical drift rates over time, which reflects the relative fluctuations in buoyancy of the animal as the proportion of lipids in the body change. Northwest Atlantic hooded seals perform drift dives at regular intervals throughout their annual migration across the Northwest Atlantic Ocean. We found that the daily change in drift rate varied with geographic location and the time of year and that this differed between sexes. Positive changes in buoyancy (reflecting increased lipid stores) were evident throughout their migration range and although overlapping somewhat, they were not statistically associated with high use areas as indicated by First Passage Time (FPT). Differences in the seasonal fluctuations of buoyancy between males and females suggest that they experience a difference in patterns of energy gain and loss during winter and spring, associated with breeding. The fluctuations in buoyancy around the moulting period were similar between sexes.     

Individualized Iterative Phenotyping for Genome-wide Analysis of Loss-of-Function Mutations

Next-generation sequencing provides the opportunity to practice predictive medicine based on identified variants. Putative loss-of-function (pLOF) variants are common in genomes and understanding their contribution to disease is critical for predictive medicine. To this end, we characterized the consequences of pLOF variants in an exome cohort by iterative phenotyping. Exome data were generated on 951 participants from the ClinSeq cohort and filtered for pLOF variants in genes likely to cause a phenotype in heterozygotes. 103 of 951 exomes had such a pLOF variant and 79 participants were evaluated. Of those 79, 34 had findings or family histories that could be attributed to the variant (28 variants in 18 genes), 2 had indeterminate findings (2 variants in 2 genes), and 43 had no findings or a negative family history for the trait (34 variants in 28 genes). The presence of a phenotype was correlated with two mutation attributes: prior report of pathogenicity for the variant (p = 0.0001) and prior report of other mutations in the same exon (p = 0.0001). We conclude that 1/30 unselected individuals harbor a pLOF mutation associated with a phenotype either in themselves or their family. This is more common than has been assumed and has implications for the setting of prior probabilities of affection status for predictive medicine.