Model of ammonia volatilization from calcareous soils

A quantitative model of ammonia volatilization from the calcareous soil uppermost 1-cm layer was developed and tested. The model accounts for the following processes: ammonium-ammonia equilibration in the soil solution, cation exchange between calcium and ammonium which results in ammonium distribution between soil liquid and solid phases, nitrification of dissolved ammonium, distribution of ammonia between liquid and gaseous phases and diffusion of gaseous ammonia in the soil air. The combined effect of various characteristics such as soil pH, cation exchange capacity, water capacity and nitrification rate on ammonia losses from various soil types have been studied. The model was validated against experimental results of ammonia losses from different soils for its use as a predicting tool. The model shows that most of ammonia losses can be explained by the interactive effect of high soil pH and low cation exchange capacity. Computations show increased ammonia volatilization with decreasing soil water capacity. Increasing fertilizer application rate has a small effect on percentage of ammonia losses. Increased nitrification rate and shorter “lag” period of nitrification reduce ammonia losses considerably. Good agreement was obtained between model calculations and experimental results of ammonia volatilization from 13 soils.     

Two-color flow cytometric analysis of monocyte depleted human blood lymphocyte subsets

Peripheral blood mononuclear cells (PBMC) from normal individuals were examined using 16 pairs of FITC and phycoerythrin (PE) directly conjugated monoclonal antibodies. Each pair of reagents was used to evaluate a conventional lymphocyte gate as well as open (non) gate of monocyte depleted PBMC. Parallel studies using the same panel of monoclonal antibodies were carried out on selected, nonmonocyte depleted samples. The major findings of this analysis were that 1,000-1,200 lymphocytes in a 10,000 cell analysis are found outside the lymphocyte gate and of these approximately 2/5 are CD16 positive LGL/NK cells, 2/5 are CD3 positive T cells, and 1/5 are CD19/CD20 positive B cells. Thus, it appears that 10-15% of the lymphoid cells fall outside of the conventional lymphocyte gate, and in certain settings monocyte depletion may be useful to perform more complete evaluation of the total lymphoid cell population obtained after ficoll-hypaque separation.     

Dexamethasone blocks increased leukotriene B4 production during endotoxin-induced lung injury

We hypothesized that leukotriene B4 (LTB4) might be produced during endotoxemia in pigs and, if so, might play a role in the pathophysiology of acute respiratory failure. Escherichia coli endotoxin (055-B5) was infused intravenously into anesthetized pigs at 5 micrograms/kg the 1st h, followed by 2 micrograms.kg-1.h-1 for 3 h. Endotoxemic pigs were treated with dexamethasone (DEX, iv) 18 h (5 mg/kg) and 1 h (5 mg/kg) before onset of endotoxemia. During phases I (i.e., 0-2 h) and II (i.e., 2-4 h), endotoxin decreased cardiac index, caused granulocytopenia, and increased mean pulmonary arterial pressure, pulmonary vascular resistance, alveolar-arterial O2 gradient, and hematocrit. During phase II, plasma LTB4 levels were increased (as determined by radioimmunoassay, reverse-phase high-performance liquid chromatography, and ultraviolet spectroscopy). Endotoxin increased the levels of LTB4 and albumin in bronchoalveolar lavage fluid (BALF). DEX blocked or greatly attenuated the endotoxin-induced hemodynamic abnormalities and blocked the increases in plasma and BALF LTB4 levels. We conclude that LTB4 is produced during porcine endotoxemia and could possibly play a role in the pathophysiology of endotoxin-induced lung injury in anesthetized pigs.     

Argininosuccinic aciduria: prenatal studies in a family at risk.

We have monitored two successive pregnancies in a family which we found to be at risk for argininosuccinic aciduria. We measured argininosuccinic acid (ASA) concentrations in amniotic fluid and utilized an indirect assay of ASA lyase activity in cultured amniotic fluid cells. The assay procedure is based on the uptake of 14C from [14C]citrulline and of [3H]leucine into protein. ASA was easily measured in amniotic fluid from the first fetus at risk, whereas none was detectable in control fluids. Amniotic fluid cells cultured from this fetus had only 5.5% of control ASA lyase activity. The pregnancy was terminated, and hepatic ASA lyase activity in the fetus was shown to be about 1.3% of control values. In addition, eight fetal tissues were analyzed for ASA, and all had significant accumulation. ASA was not detected in amniotic fluid from the second fetus at risk, and ASA lyase activity in cultured cells was 80% of control activity. Enzymatic analysis of erythrocyte lysate confirmed the diagnosis of an unaffected child (ASA lyase = 46% of control) and indicated heterozygosity. Thus, we provide further evidence that argininosuccinic aciduria can be diagnosed successfully in utero by indirect assay of ASA lyase activity in cultured amniotic fluid cells. In addition, high amniotic fluid ASA concentrations provide strong adjunctive evidence for such a prenatal determination, and may prove to be sufficient for diagnosis.     

Thin-layer chromatography of β-aminopropionitrile

Thin-layer chromatography of β-aminopropionitrile (BAPN) in acetone and 1 m ammonium hydroxide (9:1) allowed separation of that compound from amino acids present in rat-liver perfusion fluid without prior solvent extraction. Direct densitometry of the spots obtained with ninhydrin yielded satisfactory quantitation of β-aminopropionitrile present. Utilization of [¹⁴C]nitrile-labeled β-aminopropionitrile and concurrent analysis of cyanoacetic acid allowed almost complete accountability of BAPN added to isolated rat liver.     

Human-Associated Methicillin-Resistant Staphylococcus aureus from a Subtropical Recreational Marine Beach

Reports of Staphylococcus aureus including methicillin-resistant S. aureus (MRSA) detected in marine environments have occurred since the early 1990s. This investigation sought to isolate and characterize S. aureus from marine waters and sand at a subtropical recreational beach, with and without bathers present, in order to investigate possible sources and to identify the risks to bathers of exposure to these organisms. During 40 days over 17 months, 1,001 water and 36 intertidal sand samples were collected by either bathers or investigators at a subtropical recreational beach. Methicillin-sensitive S. aureus (MSSA) and MRSA were isolated and identified using selective growth media and an organism-specific molecular marker. Antimicrobial susceptibility, staphylococcal cassette chromosome mec (SCCmec) type, pulsed-field gel electrophoresis (PFGE) pattern, multi-locus sequence type (MLST), and staphylococcal protein A (spa) type were characterized for all MRSA. S. aureus was isolated from 248 (37 %) bather nearby water samples at a concentration range of <2–780 colony forming units per ml, 102 (31 %) ambient water samples at a concentration range of <2–260 colony forming units per ml, and 9 (25 %) sand samples. Within the sand environment, S. aureus was isolated more often from above the intertidal zone than from intermittently wet or inundated sand. A total of 1334 MSSA were isolated from 37 sampling days and 22 MRSA were isolated from ten sampling days. Seventeen of the 22 MRSA were identified by PFGE as the community-associated MRSA USA300. MRSA isolates were all SCCmec type IVa, encompassed five spa types (t008, t064, t622, t688, and t723), two MLST types (ST8 and ST5), and 21 of 22 isolates carried the genes for Panton–Valentine leukocidin. There was a correlation (r?=?0.45; p?=?0.05) between the daily average number of bathers and S. aureus in the water; however, no association between exposure to S. aureus in these waters and reported illness was found. This report supports the concept that humans are a potential direct source for S. aureus in marine waters.     

Autoimmune lymphoproliferative syndrome with defective Fas: genotype influences penetrance

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of lymphocyte homeostasis and immunological tolerance. Most patients have a heterozygous mutation in the APT1 gene, which encodes Fas (CD95, APO-1), mediator of an apoptotic pathway crucial to lymphocyte homeostasis. Of 17 unique APT1 mutations in unrelated ALPS probands, 12 (71%) occurred in exons 7-9, which encode the intracellular portion of Fas. In vitro, activated lymphocytes from all 17 patients showed apoptotic defects when exposed to an anti-Fas agonist monoclonal antibody. Similar defects were found in a Fas-negative cell line transfected with cDNAs bearing each of the mutations. In cotransfection experiments, Fas constructs with either intra- or extracellular mutations caused dominant inhibition of apoptosis mediated by wild-type Fas. Two missense Fas variants, not restricted to patients with ALPS, were identified. Variant A(-1)T at the Fas signal-sequence cleavage site, which mediates apoptosis less well than wild-type Fas and is partially inhibitory, was present in 13% of African American alleles. Among the ALPS-associated Fas mutants, dominant inhibition of apoptosis was much more pronounced in mutants affecting the intracellular, versus extracellular, portion of the Fas receptor. Mutations causing disruption of the intracellular Fas death domain also showed a higher penetrance of ALPS phenotype features in mutation-bearing relatives. Significant ALPS-related morbidity occurred in 44% of relatives with intracellular mutations, versus 0% of relatives with extracellular mutations. Thus, the location of mutations within APT1 strongly influences the development and the severity of ALPS.     

Iron alters glutamate secretion by regulating cytosolic aconitase activity

Glutamate has many important physiological functions, including its role as a neurotransmitter in the retina and the central nervous system. We have made the novel observations that retinal pigment epithelial cells underlying and intimately interacting with the retina secrete glutamate and that this secretion is significantly affected by iron. In addition, iron increased secretion of glutamate in cultured lens and neuronal cells, indicating that this may be a common mechanism for the regulation of glutamate production in many cell types. The activity of the iron-dependent enzyme cytosolic aconitase (c-aconitase) is increased by iron. The conversion of citrate to isocitrate by c-aconitase is the first step in a three-step process leading to glutamate formation. In the present study, iron increased c-aconitase activity, and this increase was associated with an increase in glutamate secretion. Inhibition of c-aconitase by oxalomalate decreased glutamate secretion and completely inhibited the iron-induced increase in glutamate secretion. Derangements in both glutamate secretion and iron metabolism have been noted in neurological diseases and retinal degeneration. Our results are the first to provide a functional link between these two physiologically important substances by demonstrating a significant role for iron in the regulation of glutamate production and secretion in mammalian cells resulting from iron regulation of aconitase activity. Glutamatergic systems are found in many nonneuronal tissues. We provide the first evidence that, in addition to secreting glutamate, retinal pigment epithelial cells express the vesicular glutamate transporter VGLUT1 and that regulated vesicular release of glutamate from these cells can be inhibited by riluzole. retinal pigment epithelial cells; lens epithelial cells     

Haemorrhage as a Complication of Extracorporeal Pig Liver Perfusion: Studies on Mechanism and Prevention

The use of extracorporeal pig liver perfusion for temporary liver support has been followed not infrequently by major bleeding with a fall in coagulation factors and platelets, rather than a rise as hoped. In 18 experimental perfusions in which ¹²⁵I-labelled fibrinogen was used as a marker there was in every instance a significant loss of the fibrinogen into the fluid supporting the liver in the perfusion chamber. Further, in 11 of the perfusions there was an additional loss into liver substance, this being associated with a very rapid fall in ¹²⁵I fibrinogen and platelets content of the perfusion fluid. Damage to the sinusoids from ischaemic damage incurred during removal of the liver could explain both the direct loss of fibrinogen and, as a result of intravascular coagulation, the associated loss within the perfused liver. No correlation could be found with biochemical function, but it proved possible to assess haematological safety before connexion of the patient to the perfusion by a shortened ¹²⁵I fibrinogen test. This was done in three patients treated by five perfusions and in none was the thrombocytopenia or coagulation disturbance adversely affected.     

Native C3 does not bind to the C3b receptor (CR1) of human blood B lymphocytes or alter immunoglobulin synthesis

Complement receptors on lymphocytes were first described more than 12 yr ago (1-3) and have come to be used as a common marker for the identification of B cells (4). The function of these receptors on the lymphocyte and their possible role in induction and/or regulation of the immune response remain unclear. In particular, there continues to be controversy as to whether native C3 can bind to the C3b receptor of these cells without cleavage to C3b (5-10). The resolution of this question is critical in order to clarify the expected state of availability of the receptor in vivo, because in plasma, the C3 concentration is relatively high (1.1 to 1.5 mg/ml), whereas there is little or no circulating C3b due to efficient degradation by factor H and the C3-inactivator (11). With the recent development of an improved method for the isolation of C3 from human plasma, it has been possible to obtain biochemically and functionally pure C3 that has not undergone structural or conformational alteration during processing and fully retains the specific hemolytic activity of C3 in fresh serum (12). Berger et al. (13) were able to demonstrate that C3 prepared in this way failed to bind to the C3b receptor of human polymorphonuclear leukocytes or erythrocytes. Similar observations were made by Schreiber et al. (14), also with phagocytic cells and erythrocytes, and by Dixit et al. (15) with an isolated membrane receptor preparation from rabbit macrophages. In the present communication, we extend these observations to human peripheral blood B lymphocytes. Purified C3 in its native state fails to block B lymphocyte-EA (IgM) C4b3b rosettes, whereas C3b causes 50% inhibition at 5 to 6 micrograms/ml. Furthermore, C3 failed to alter polyclonal immunoglobulin (Ig) production by human B cells, whereas C3b inhibited this B cell function. These data suggest that native C3 does not bind to the C3b receptors of B lymphocytes, and thus they are not occupied under normal conditions in vivo.