Arginase attenuates inhibitory nonadrenergic noncholinergic nerve-induced nitric oxide generation and airway smooth muscle relaxation

Background

Recent evidence suggests that endogenous arginase activity potentiates airway responsiveness to methacholine by attenuation of agonist-induced nitric oxide (NO) production, presumably by competition with epithelial constitutive NO synthase for the common substrate, L-arginine. Using guinea pig tracheal open-ring preparations, we now investigated the involvement of arginase in the modulation of neuronal nitric oxide synthase (nNOS)-mediated relaxation induced by inhibitory nonadrenergic noncholinergic (iNANC) nerve stimulation.

Methods

Electrical field stimulation (EFS; 150 mA, 4 ms, 4 s, 0.5 – 16 Hz)-induced relaxation was measured in tracheal preparations precontracted to 30% with histamine, in the presence of 1 μM atropine and 3 μM indomethacin. The contribution of NO to the EFS-induced relaxation was assessed by the nonselective NOS inhibitor L-NNA (0.1 mM), while the involvement of arginase activity in the regulation of EFS-induced NO production and relaxation was investigated by the effect of the specific arginase inhibitor nor-NOHA (10 μM). Furthermore, the role of substrate availability to nNOS in EFS-induced relaxation was measured in the presence of various concentrations of exogenous L-arginine.

Results

EFS induced a frequency-dependent relaxation, ranging from 6.6 ± 0.8% at 0.5 Hz to 74.6 ± 1.2% at 16 Hz, which was inhibited with the NOS inhibitor L-NNA by 78.0 ± 10.5% at 0.5 Hz to 26.7 ± 7.7% at 8 Hz (P < 0.01 all). In contrast, the arginase inhibitor nor-NOHA increased EFS-induced relaxation by 3.3 ± 1.2-fold at 0.5 Hz to 1.2 ± 0.1-fold at 4 Hz (P < 0.05 all), which was reversed by L-NNA to the level of control airways in the presence of L-NNA (P < 0.01 all). Similar to nor-NOHA, exogenous L-arginine increased EFS-induced airway relaxation (P < 0.05 all).

Conclusion

The results indicate that endogenous arginase activity attenuates iNANC nerve-mediated airway relaxation by inhibition of NO generation, presumably by limiting L-arginine availability to nNOS.     

TP53 mutations in human meningiomas

Overexpression of p53 has been reported to play a role in the development of neoplasms of the central nervous system. Meningiomas are generally benign intracranial tumors originating from the meninges. Overexpression of the p53 protein in meningiomas and an association with histological type and recurrence has been reported. Mutation of the TP53 gene leads to a more stable p53 protein in quantities high enough for detection by immunohistochemistry. In the search for these mutations the core domain of the TP53 gene of meningiomas has been analyzed. Only a very low incidence of mutations was reported. The apparent discordance between overexpression of p53 protein and TP53 gene mutations may be explained by mutations located outside the core domain. This issue was addressed in the present study. All 11 exons of 17 meningiomas were analyzed for DNA alterations by PCR single-strand conformation polymorphism (PCR-SSCP) analysis with subsequent sequencing. PCR-SSCP analysis showed a various number of band shifts and nucleotide alterations, caused either by alterations in the flanking introns or common polymorphisms (codon 36 and 72). The allele frequencies of the polymorphisms found in this small population of tumors resemble the frequencies reported in the literature. In addition, three nucleotide changes located in introns 2, 3 and 7 were found in 11, 3 and 4, respectively, of 17 specimens. Based on this study and on reports by others we conclude that it is not very likely that TP53 mutations are involved in the etiology of meningiomas.     

Identification of Two Protein-Signaling States Delineating Transcriptionally Heterogeneous Human Medulloblastoma

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Bioassay responses of micro-organisms to sediment elutriates from the St. Lawrence River (Lake St. Louis)

A sediment study, involving both chemical and biological analyses, was carried out in the St. Lawrence River near Montreal (Lake St. Louis). About 60 stations were sampled during 1984–85, and the sediments were analyzed for support variables, heavy metals, and organochlorinated compounds. Subsamples were elutriated using a 1 to 4 sediment/water ratio. The resulting elutriates were analyzed for several chemical variables, while toxicity was measured using the Microtox test, algal ¹⁴C assimilation, and lethality/developmental inhibition in cladocerans, rotifers, and nematodes. The results showed a great variety of responses and sensitivity, and correlations between the tests were non-significant. In terms of toxic responses, the algal and Microtox tests were the most sensitive. Toxic responses could not be explained in simple terms of contaminant concentrations. Therefore, the chemistry of elutriates is not predictive of the toxic potential of contaminated sediments. Biotests can give an insight into the hazard assessment of sediments, but no single test will be sufficient; the use of a battery of standardized biotests, representing different levels of organization/food chain, including representative natural species, is highly recommended.     

Competition for Sulfate and Ethanol Among Desulfobacter, Desulfobulbus, and Desulfovibrio Species Isolated from Intertidal Sediments

Competition for sulfate and ethanol among Desulfobacter, Desulfobulbus, and Desulfovibrio species isolated from estuarine sediments was studied in energy-limited chemostats. Desulfovibrio baculatus was the most successful competitor for limiting amounts of sulfate and ethanol, followed by Desulfobulbus propionicus. The success of Desulfovibrio baculatus was dependent on the availability of sufficient iron. Of the three species studied, Desulfobacter postgatei was the least successful competitor for limiting amounts of sulfate. Although stimulating the growth of Desulfobacter postgatei, addition of Ca-saturated illite particles to culture media did not affect the outcome of competition for sulfate. Thus, under sulfate limitation acetate accumulated. This phenomenon was briefly discussed in relation to the flow of electrons during anaerobic mineralization in marine and estuarine sulfate-limited sediments.     

Cardiovascular and Valsalva responses during parabolic flight

We investigated the integrated cardiovascularresponses of 15 human subjects to the acute gravitational changes(micro- and hypergravity portions) of parabolic flight. Measurementswere made with subjects quietly seated and while subjects performed controlled Valsalva maneuvers. During quiet, seated, parabolic flight,mean arterial pressure increased during the transition into microgravity but decreased as microgravity was sustained. Thedecrease in mean arterial pressure was accompanied by immediate reflexive increases in heart rate but by absent (orlater-than-expected) reflexive increases in total vascular resistance.Mean arterial pressure responses in Valsalva phasesII_l, III, and IV wereaccentuated in hypergravity relative to microgravity(P < 0.01, P < 0.01, andP < 0.05, respectively), butaccentuations differed qualitatively and quantitatively from thoseinduced by a supine-to-seated postural change in 1 G. This study is thefirst systematic evaluation of temporal and Valsalva-related changes incardiovascular parameters during parabolic flight. Results suggest thatarterial baroreflex control of vascular resistance may be modified byalterations of cardiopulmonary, vestibular, and/or otherreceptor activity.

     

Lipase kinetics: hydrolysis of triacetin by lipase from Candida cylindracea in a hollow-fiber membrane reactor

The aptitude of a hollow-fiber membrane reactor to determine lipase kinetics was investigated using the hydrolysis of triacetin catalyzed by lipase from Canadida cylindracea as a model system. The binding of the lipase to the membrane appears not to be very specific (surface adsorption), and probably its conformation is hardly altered by immobilization, resulting in an activity comparable to that of the enzyme in its native form. The reaction kinetics defined on the membrane surface area were found to obey Michaelis-Menten kinetics. The specific activity of the lipase in the membrane reactor was found to be significantly higher than in an emulsion reactor. The activity and stability of the enzyme immobilized on a hydrophilic membrane surface seem not to be influenced significantly by the choice of the membrane material. The hollow-fiber membrane reactor is a suitable tool to assess lipase kinetics in a fast and convenient way.     

Community structure of the epipelagic zooplankton community under the sea-ice of the northern Weddell Sea

Summary The present paper describes the composition, abundance, biomass and diversity of the meso- and macrozooplankton in the epipelagic zone of the open water and under the ice of the northern Weddell Sea. Samples were collected in October/November 1988 with a multiple RMT1+8 net during the European Polarstern Study (EPOS). Multivariate analysis resulted in two distinct site clusters, a northern one mainly located in the open water/marginal ice zone and a southern one extending from the marginal ice zone into the consolidated pack-ice. Clusters were, however, faunistically coherent with a high degree in positive covariation of species. There was no basis for the separation into communities, but differences occurred on the population level in numerical abundances, biomass (wet weight) and in a shift in species dominance. Different ice zones and vertical layers were tested among each other with regard to their relative species abundance. Significant differences were found between the upper 60 m layer of the open sea, the upper 60 m layer of the closed pack-ice and the so called transitional zone. Species richness and diversity was lowest directly under the closed pack-ice. Abundance and biomass was highest in the surface layer of the open water, while both variablès decreased dramatically under the ice. Copepods dominated numerically in open water, while salps dominated in biomass. Euphausia superba and Thysanoessa macrura were the dominant species in the upper water column of the closed pack-ice zone. Krill was the only species with increasing abundance in the sub-ice area and a dominance in biomass of more than 91% demonstrated its unique importance for the sub-ice habitat.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Discriminative ability and function of the immunobiological recognition system of the snailHelix pomatia

Summary The internal defense mechanism ofHelix pomatia discriminates between different types of foreign cells as demonstrated by determinations of their clearance rates. The rate of elimination is not dependent on the size of foreign cells but on their molecular surface properties. Circulating hemocytes are not involved in the first phase of the clearance event, which is characterized by an accumulation of nonself cells in the digestive gland, kidney and foot muscle ofHelix. Light microscopic studies of these organs reveal nonself cells to be attached to the membrane of cells lining hemolymph sinuses. The attachment of certain types of foreign cells is apparently mediated by opsonins as their clearance depends on the opsonin level of the hemolymph, whereas others are cleared without involvement of opsonizing molecules. Membrane bound molecules of the latter type of nonself cells seem to directly interact with carbohydrate-specific combining sites on the membranes of cells of the sinus walls, as their binding can be inhibited by N-acetyl-galactosamine, and N-acetyl-glucosamine.The second phase of clearance apparently involves the attraction of circulating hemocytes by organtrapped foreign cells. The number of hemocytes in circulation decreases significantly, whereafter a rising percentage of hemocytes containing foreign cells can be observed in the circulation.