Presence Of Ne Research Articles

Isotopic compositions of C, N, O, Mg, and Si, trace element abundances, and morphologies of single circumstellar graphite grains in four density fractions from the Murchison meteorite

We report ion microprobe determinations of carbon, nitrogen, oxygen, magnesium-aluminum, and silicon isotopic compositions and trace element (H, N, O, Al, Si) concentrations of individual graphite grains (0.8–28 pm) from the Murchison CM2 chondrite. The analyzed grains exhibit large variations of their isotopic compositions: 12C/ 13C ratios vary by a factor of 3500, 14N/ 15N ratios by a factor of 24, and 16O/ 18O ratios by a factor of 14. Most grains have isotopically light carbon and heavy nitrogen and excesses in 18O are positively correlated with excesses in 15N. According to their carbon isotopic composition and density we distinguish between four different groups of graphite grains. Many grains show large 26Mg excesses with inferred 26Al/ 27Al ratios ranging up to 0.1. Highest 26Al/ 27Al ratios are found in grains with close-to-normal carbon isotopic composition. Most grains have normal Si but some have large silicon isotopic anomalies. One of these grains has isotopic characteristics similar to those of the rare SiC grains of type X. Nitrogen contents are roughly correlated with the contents of other trace elements. Grains with isotopically heavy carbon tend to have higher trace element contents than grains with isotopically light carbon. Most graphite grains (∼ -92%) are round and dense. These grains either have smooth surfaces or appear to consist of dense aggregates of small scales. These surface morphologies are reflected in the internal structure of the grains. The morphology of graphite grains correlates with isotopic properties as only round grains have carbon isotopic anomalies, although small nitrogen anomalies are present in both round and nonround grains, and as morphologic subtypes of round grains are distributed differently over the range of 12C/ 13C ratios. Combining both carbon isotopic compositions and morphologies we distinguish between six different groups of round graphite grains. The isotopic characteristics of most graphite grains strongly differ from those of circumstellar SiC, suggesting that these two types of circumstellar grains originate from distinct stellar sources. Wolf-Rayet stars and Type II supernovae seem to account for the isotopic properties of most (>60%) circumstellar graphite grains. The presence of Ne E (L) with 20Ne/ 22Ne < 0.087, the lower limit for He-shell Ne, and isotopically heavy carbon together with heavy nitrogen indicate that some grains (<I%) originate from novae. Evidence for an AGB star origin comes from Kr S, but only few grains have isotopically heavy carbon and light nitrogen, expected from present stellar and nucleosynthetic models of these stars.

Adenosine receptor activation potentiates phosphoinositide hydrolysis and arachidonic acid release in DDT 1-MF2 cells: Putative interrelations

Studies were undertaken in an effort to discern possible mechanisms by which the A 1 adenosine receptor agonist cyclopentyladenosine (CPA) enhances the norepinephrine-stimulated (NE-stimulated) hydrolysis of phosphoinositides in DDT 1-MF2 cells. Measurements of arachidonic acid release revealed similar behaviours to those observed in measurements of phosphoinositide hydrolysis. In the presence of NE, both second messenger responses were potentiated by the addition of CPA, whereas in the absence of NE, CPA had little or no effect on either second messenger. The stimulation and potentiation of both second messenger responses were enhanced in the presence of extracellular calcium, and in each case these effects were persistent over time. For either second messenger system the stimulation by NE and the potentiations by CPA appeared to utilize separate mechanisms as evidenced by the fact that the potentiations by CPA were selectively antagonized by a cAMP analogue or by pertussis toxin, whereas the stimulations by NE were essentially unaffected by these agents. Inhibition of phospholipase A 2 (PLA 2) also blocked the potentiation of PLC by CPA, without affecting NE-stimulated phosphoinositide hydrolysis. Furthermore, in the presence of CPA, the exogenous administration of PLA 2 was found to stimulate phosphoinositide hydrolysis in these cells. These data are consistent with a hypothesis whereby the apparent potentiation of NE-stimulated phosphoinositide hydrolysis by CPA is actually due to the stimulation by CPA of a second pathway of phospholipase C activity which is additive to that of NE. The activation of PLC and PLA 2 by NE produces phospholipid products which may play a permissive role in the pathway coupling adenosine A 1 receptors to these phospholipases. The formation of lysophosphatidic acid is suggested as one possible mediator of this permissive effect.

Blood pressure lowering by pioglitazone. Evidence for a direct vascular effect.

To examine potential mechanisms for the blood pressure-lowering action of the thiazolidinedione compound, pioglitazone (PIO), we studied the effects of the drug on blood pressure and insulin action in vivo and on vascular tissue in vitro. In vivo, PIO lowered blood pressure in fructose-fed and chow-fed rats to an extent that could not be explained by alterations in fasting plasma insulin or free magnesium concentrations or by alterations in whole-body insulin sensitivity. In vitro, PIO caused significant blunting of the contractile responses of aortic rings to NE, arginine vasopressin (AVP), and potassium chloride; the blunting of responses to NE was maintained after removal of the endothelium. To assess the potential importance of extracellular calcium to the vasodepressor effect of PIO, we measured contractile responses to NE in the absence of calcium, and then after acute restoration of calcium in the presence of NE. PIO had no effect on the contractile response in the absence of calcium. By contrast, PIO blunted by 42% the contractile response that occurred when the extracellular calcium supply was acutely restored in the presence of NE, suggesting that the blunting was mediated by blockade of calcium uptake by vascular smooth muscle. Such an effect was confirmed in cultured a7r5 vascular smooth muscle cells, which exhibited a brisk increase in intracellular calcium in response to AVP that was blocked by PIO in a dose-dependent fashion. Our data indicate that PIO has a direct vascular effect that appears to be mediated at least in part by inhibition of agonist-mediated calcium uptake by vascular smooth muscle. The direct vascular effect may contribute to the blood pressure-lowering actions of PIO in vivo, because that effect could not be explained by alterations in whole-body insulin sensitivity.

Incorporation of helium, neon, argon, krypton, and xenon into fullerenes using high pressure

To investigate the spectroscopic and other properties of these interesting noble gas compounds, it is necessary to increase the fraction of fullerene molecules occupied. We have done this by carrying out the incorporation step at high pressures of the gas. Part-per-million levels of the noble gases produce no measurable effects in the conventional mass spectrum, since the peaks due to ions containing these atoms are well below the noise level. However, samples of fullerene heated in the presence of Ne (38,000 psi, 66% recovery), Ar (40,000 psi, 45% recovery), Kr (24,500 psi, 25% recovery), and Xe (18,000 psi, 45% recovery) show distinct and reproducible peaks (electron impact ionization) for fullerene ions containing the noble gases. The theoretical mass spectra of the corresponding adducts were calculated using the natural isotopic abundance of the involved atoms. Agreement between calculated and experimental curves provides convincing evidence that Ne C[sub 60], Ar C[sub 60], Kr C[sub 60], Xe C[sub 60], Ne C[sub 70], Ar C[sub 70], Kr C[sub 70], and Xe C[sub 70] have been synthesized. 18 refs., 2 figs.

Collision-enhanced resonance of laser-diode-excited Cs in a buffer gas.

We report an experimental investigation of the Cs ${\mathit{D}}_{2}$ line-shape changes due to laser-induced optical pumping and collisions in a buffer gas. A model dealing with the population of the ground-state hyperfine levels, the pressure broadening in the presence of Ne, and the diffusion of the atoms outside the laser beam describes well the complex line shapes.

Alpha-adrenergic modulation of ionic currents in cultured parasympathetic neurons from rat intracardiac ganglia

1. Modulation of ionic conductances by alpha-adrenergic agonists was investigated in cultured parasympathetic neurons from rat intracardiac ganglia. Application of norepinephrine (NE, 25-100 microM) to the soma of isolated neurons reversibly reduced both the amplitude and duration of the Ca(2+)-dependent action potential evoked by injection of depolarizing current when Na+ and K+ currents were blocked pharmacologically. 2. In the whole-cell voltage-clamp mode, application of NE reversibly reduced the amplitude and rate of activation of Ca2+ current (ICa). The amplitude inhibition was greater at the peak of the current (55%) than at the end of a 700-ms pulse (20%). Maximal doses of NE produced only approximately 60% inhibition of peak ICa amplitude. 3. Inactivation of ICa was best fit by the sum of two exponential functions in the absence of NE, but was described by a single exponential function in the presence of NE. These results suggest that NE preferentially inhibited a fast inactivating component of the Ca2+ current in these parasympathetic neurons. 4. NE reversibly reduced the amplitude of Ba2+ tail currents through open Ca channels at all voltages from -40 to +150 mV with a slight shift in the activation curve determined from the current-voltage (I-V) relationship for the tail currents. NE did not change the voltage dependence of the steady-state inactivation of the calcium channels. 5. NE inhibited Ca2+ current either in the absence or presence of nifedipine but to a lesser extent in the presence of omega-conotoxin (omega-CGTX), suggesting that the Ca channels inhibited by NE are predominantly omega-CGTX sensitive. 6. The inhibition of ICa by NE was mimicked by the alpha 1-adrenergic agonists methoxamine and phenylephrine and potentiated in the presence of the alpha 2-adrenoceptor antagonist yohimbine (10 microM). NE inhibition of ICa was antagonized by bath application of the alpha-adrenergic antagonist phentolamine (1 microM), but not by prazosin (1-10 microM), yohimbine, or the beta-adrenergic antagonist propranolol (1 microM). Taken together, these results suggest that NE inhibition of Ca2+ current in rat parasympathetic cardiac neurons is mediated by an alpha-adrenergic receptor with properties that may differ from alpha 1- and alpha 2-adrenoceptors. 7. In approximately 35% of neurons studied, NE not only reduced depolarization-activated inward Ca2+ current but also increased an outward current, with a shift of the I-V curve and reversal potential to more negative voltages.(ABSTRACT TRUNCATED AT 400 WORDS)

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Stimulation of amino acid uptake and Na+,K+-ATPase activity by norepinephrine in superior cervical sympathetic ganglia excised from adult rats.

Active uptake of a labelled nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB), into isolated superior cervical sympathetic ganglia (SCG) excised from adult rats was considerably stimulated by the addition of either norepinephrine (NE, 50 microM) or 3,4-dihydroxyphenylethylamine (dopamine, DA, 100 microM) to the medium during aerobic incubation for 2 h at 37 degrees C. The NE-induced increase in AIB uptake was significantly antagonized by the addition of an alpha 1-adrenoceptor antagonist (prazosin, 10 microM) in SCG axotomized 1 week prior to the examination, in which most of the ganglionic neurons had degenerated and reactive proliferation of the satellite glial components was in progress. The addition of neither acetylcholine (ACh, 1 mM) plus eserine (0.1 mM) nor cyclic nucleotides (1 mM) changed the AIB uptake by the SCG. In the axotomized SCG, the NE-evoked increase in AIB uptake was much more pronounced than that of intact or denervated SCG. A kinetic study of the active AIB uptake in the SCG showed that NE produced a decrease of the Km value and an increase in the Vmax, especially in the axotomized SCG. Ganglionic Na+, K+-ATPase activity was greatly stimulated in the presence of NE, but not by ACh. These results strongly suggest that the NE-induced enhancement of active AIB uptake in the isolated SCG is occurring in glial cells rather than in neuronal cells, with a possible alteration of membrane properties for amino acid uptake and with an apparent regulation by the stimulated transport enzyme Na+, K+-ATPase.

Magnetic field dependence of the spin relaxation rate in optically oriented mercury vapour

The magnetic field dependence of the relaxation rate of 199Hg has been investigated at low fields in the presence of Ne or N 2. It is shown that there is a correlation time, in the interaction of the Hg nuclear spin with the walls, that is equal to the time between wall collisions. The diffusion coefficients of Hg into N 2 and Ne are evaluated, and the possibility of investigating other correlation times is discussed.

Aggregation of platelets of normal and Bordetella pertussis vaccinated mice by ATP, ADP, AND sodium fluoride.

The results of the present studies have shown that platelets obtained from &lt;i&gt;B. pertussis&lt;/i&gt; vaccinated mice were more sensitive to the aggregative action of ATP, ADP, and sodium fluoride than were their normal counterparts. Aggregation initiated by any of these substances was suppressed by exogenous cAMP but was enhanced in the presence of NE. These data suggested a role of adenyl cyclase and adrenergic receptors in the mouse platelet aggregation with the exaggerated responsiveness of ‘pertussis’ components due to either hyperreactive α-type or blockade of the &lt;i&gt;β&lt;/i&gt;-type receptors.