Carbachol and bradykinin elevate cyclic AMP and rapidly deplete ATP in cultured rat sympathetic neurons

The agonists carbachol (CCh) and bradykinin (BK) and 54 mM KCl (high K+) were among the most potent stimulants of cyclic AMP (cAMP) production in cultured rat sympathetic neurons, measured with the use of a high-fidelity assay developed for small samples. The rise in cAMP evoked by CCh (through muscarinic receptors), BK, and high K+ was inhibited in Ca2(+)-depleted medium (1.3 mM Ca2+ and 2 mM BAPTA or EGTA), which also prevented the sustained rise in [Ca2+]i evoked by each of these stimuli, showing that elevation of cAMP requires extracellular Ca2+ and, possibly, Ca2+ influx. Preliminary results obtained with the novel calmodulin inhibitor CGS 9343B, which blocked the elevation of cAMP, and with the cyclogenase inhibitor indomethacin, which partially blocked the actions of the agonists but not those of high K+, suggest that calmodulin and arachidonate metabolites may be two components of the signaling pathway. In addition to their effects on cAMP metabolism, CCh, muscarine, and BK, but not nicotine, caused a 30-40% decrease in ATP levels. This effect was much greater than that evoked by high K+ and was largely inhibited by CGS 9343B but slightly enhanced in the Ca(+)-depleted medium, showing that agonists are still active in the absence of [Ca2+]o. Thus, agonists that activate phosphoinositide metabolism can also increase cAMP production and substantially deplete cells of ATP. These novel actions may have to be taken into account when the mechanisms by which such agonists regulate cell function are being considered

Seeing Laure: Race and Modernity from Manet's Olympia to Matisse, Bearden and Beyond

During the 1860s in Paris, Edouard Manet and his circle transformed the style and content of art to reflect an emerging modernity in the social, political and economic life of the city. Manet's Olympia (1863) was foundational to the new manner of painting that captured the changing realities of modern life in Paris. One readily observable development of the period was the emergence of a small but highly visible population of free blacks in the city, just fifteen years after the second and final French abolition of territorial slavery in 1848. The discourse around Olympia has centered almost exclusively on one of the two figures depicted: the eponymous prostitute whose portrayal constitutes a radical revision of conventional images of the courtesan. This dissertation will attempt to provide a sustained art-historical treatment of the second figure, the prostitute's black maid, posed by a model whose name, as recorded by Manet, was Laure. It will first seek to establish that the maid figure of Olympia, in the context of precedent and Manet's other images of Laure, can be seen as a focal point of interest, and as a representation of the complex racial dimension of modern life in post-abolition Paris. It will then examine the continuing resonance and influence of Manet's Laure across successive generations of artists from Manet's own time to the present moment. The dissertation thereby suggests a continuing iconographic lineage for Manet's Laure, as manifested in iteratively modernizing depictions of the black female figure from 1870 to the present. Artworks discussed include a clarifying homage to Manet by his acolyte Frédéric Bazille; the countertypical portrayal by early modernist Henri Matisse of two principal black models as personifications of cosmopolitan modernity; the presentation by collagist Romare Bearden of a black odalisque defined by cultural, rather than sexual, attributes metaphoric of the cultural hybridity of African American culture; and direct engagement with Manet's depiction of Laure by selected contemporary artists, including Maud Sulter and Mickalene Thomas, often with imagery, materials and processes also influenced by Matisse or Bearden. In each case, the fitfully evolving modernity of the black female figure will be seen to emerge from each artist's fidelity to his or her transformative creative vision regardless of the representational norms of the day. The question of what, if anything, is represented by Manet's idiosyncratic depiction of the prostitute's black maid has seldom been comprehensively addressed by the histories of modern art. The small body of published commentary about Manet's Laure, with a few notable exceptions, generally dismisses the figure as meaning, essentially, nothing -- except as an ancillary intensifier of the connotations of immorality attributed to the prostitute. Manet's earlier portrait of Laure, rich in significations relevant to her portrayal in Olympia, is even more rarely discussed, and typically seen as a study for Olympia, rather than as a stand-alone portrait as this analysis suggests. The image of Laure as Olympia's maid is frequently oversimplified as a racist stereotype, a perspective that belies the metonymic implications of a figure that is simultaneously centered and obscured. It is in the extensive body of response to Laure's Olympia pose by artists, more than by historians, that the full complexity and enduring influence of the figure's problematic nuance can be seen. This dissertation, like the artists, takes its cues from the formal qualities of Manet's images of Laure, in the context of precedent images and the fraught racial interface within Manet's social and artistic milieu, to suggest new and revisionary narratives. It suggests that Manet's Laure can be seen as an early depiction of an evolving cultural hybridity among black Parisians- visible in Laure's placement, affect and attire--that took shape during the early years of the newly built northern areas of Paris that are today home to some of the largest black populations in central Paris. Within this context, an iconographic legacy of ambivalent yet innovative modernity can be asserted for the Laure figure -extending from Delacroix to Matisse, Bearden and beyond. This lineage can be seen as parallel to the long-established pictorial lineage for Manet's figuring of the prostitute Olympia. What is at stake is an art-historical discourse posed as an intervention with the prevailing historical silence about the representation and legacy of Manet's Laure, and by derivation about the significance of the black female muse to the formation of modernism. This analysis suggests that the black female figure is foundational to the evolving aesthetics of modern art. It suggests that Olympia's standing as a progenitor of modern painting can only be enhanced by breaking through the marginalization of Laure's representational legacy. It asserts that it is only when the bi-figural significance of Manet's Olympia is recognized that the extent and influence of Manet's radical modernity can be most fully understood

Draft Genome Sequences of Facultative Methylotrophs, Gemmobacter sp. Strain LW1 and Mesorhizobium sp. Strain 1M-11, Isolated from Movile Cave, Romania

Facultative methylotrophs belonging to the genera Gemmobacter and Mesorhizobium were isolated from microbial mat and cave water samples obtained from the Movile Cave ecosystem. Both bacteria can utilize methylated amines as their sole carbon and nitrogen source. Here, we report the draft genome sequences of Gemmobacter sp. strain LW1 and Mesorhizobium sp. strain IM1

Ca2+ transients are not required as signals for long-term neurite outgrowth from cultured sympathetic neurons

A method for clamping cytosolic free Ca2+ ([Ca2+]i) in cultures of rat sympathetic neurons at or below resting levels for several days was devised to determine whether Ca2+ signals are required for neurite outgrowth from neurons that depend on Nerve Growth Factor (NGF) for their growth and survival. To control [Ca2+]i, normal Ca2+ influx was eliminated by titration of extracellular Ca2+ with EGTA and reinstated through voltage-sensitive Ca2+ channels. The rate of neurite outgrowth and the number of neurites thus became dependent on the extent of depolarization by KCl, and withdrawal of KCl caused an immediate cessation of growth. Neurite outgrowth was completely blocked by the L type Ca2+ channel antagonists nifedipine, nitrendipine, D600, or diltiazem at sub- or micromolar concentrations. Measurement of [Ca2+]i in cell bodies using the fluorescent Ca2+ indicator fura-2 established that optimal growth, similar to that seen in normal medium, was obtained when [Ca2+]i was clamped at resting levels. These levels of [Ca2+]i were set by serum, which elevated [Ca2+]i by integral of 30 nM, whereas the addition of NGF had no effect on [Ca2+]i. The reduction of [Ca2+]o prevented neurite fasciculation but this had no effect on the rate of neurite elongation or on the number of extending neurites. These results show that neurite outgrowth from NGF-dependent neurons occurs over long periods in the complete absence of Ca2+ signals, suggesting that Ca2+ signals are not necessary for operating the basic machinery of neurite outgrowth

The stoichiometry of P2X2/6 receptor heteromers depends on relative subunit expression levels

Fast synaptic transmission involves the operation of ionotropic receptors, which are often composed of at least two types of subunit. We have developed a method, based on atomic force microscopy imaging to determine the stoichiometry and subunit arrangement within ionotropic receptors. We showed recently that the P2X(2) receptor for ATP is expressed as a trimer but that the P2X(6) subunit is unable to oligomerize. In this study we addressed the subunit stoichiometry of heteromers containing both P2X(2) and P2X(6) subunits. We transfected tsA 201 cells with both P2X(2) and P2X(6) subunits, bearing different epitope tags. We manipulated the transfection conditions so that either P2X(2) or P2X(6) was the predominant subunit expressed. By atomic force microscopy imaging of isolated receptors decorated with antiepitope antibodies, we demonstrate that when expression of the P2X(2) subunit predominates, the receptors contain primarily 2 x P2X(2) subunits and 1 x P2X(6) subunit. In contrast, when the P2X(6) subunit predominates, the subunit stoichiometry of the receptors is reversed. Our results show that the composition of P2X receptor heteromers is plastic and dependent on the relative subunit expression levels. We suggest that this property of receptor assembly might introduce an additional layer of subtlety into P2X receptor signaling

Interplay between substrate rigidity and tissue fluidity regulates cell monolayer spreading

Coordinated and cooperative motion of cells is essential for embryonic development, tissue morphogenesis, wound healing and cancer invasion. A predictive understanding of the emergent mechanical behaviors in collective cell motion is challenging due to the complex interplay between cell-cell interactions, cell-matrix adhesions and active cell behaviors. To overcome this challenge, we develop a predictive cellular vertex model that can delineate the relative roles of substrate rigidity, tissue mechanics and active cell properties on the movement of cell collectives. We apply the model to the specific case of collective motion in cell aggregates as they spread into a two-dimensional cell monolayer adherent to a soft elastic matrix. Consistent with recent experiments, we find that substrate stiffness regulates the driving forces for the spreading of cellular monolayer, which can be pressure-driven or crawling-based depending on substrate rigidity. On soft substrates, cell monolayer spreading is driven by an active pressure due to the influx of cells coming from the aggregate, whereas on stiff substrates, cell spreading is driven primarily by active crawling forces. Our model predicts that cooperation of cell crawling and tissue pressure drives faster spreading, while the spreading rate is sensitive to the mechanical properties of the tissue. We find that solid tissues spread faster on stiff substrates, with spreading rate increasing with tissue tension. By contrast, the spreading of fluid tissues is independent of substrate stiffness and is slower than solid tissues. We compare our theoretical results with experimental results on traction force generation and spreading kinetics of cell monolayers, and provide new predictions on the role of tissue fluidity and substrate rigidity on collective cell motion

Partitioning of K, U, and Th between sulfide and silicate liquids: Implications for radioactive heating of planetary cores

The possibility of heating of planetary cores by K radioactivity has been extensively discussed, as well as the possibility that K partitioning into the terrestrial core is the reason for the difference between the terrestrial and chondritic K/U. We had previously suggested that U and Th partitioning into FeFeS liquids was more important than K. Laboratory FeFeS liquid, silicate liquid partition coefficient measurements (D) for K, U, and Th were made to test this suggestion. For a basaltic liquid at 1450°C and 1.5 GPa, D_U is 0.013 and D_K is 0.0026; thus U partitioning into FeFeS liquids is 5 times greater than K partitioning under these conditions. There are problems with 1-atm experiments in that they do not appear to equilibrate or reverse. However, measurable U and Th partitioning into sulfide was nearly always observed, but K partitioning was normally not observed (D_K ≲ 10^(−4)). A typical value for D_U from a granitic silicate liquid at one atmosphere, 1150°C, and low f0_2 is about 0.02; D_(Th) is similar. At low f0_2 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with D_U > 1. D_(Th) is less strongly affected. Because of the consistently low D_K/D_U, pressure effects near the core-mantle boundary would need to increase D_U by factors of ∼10^3 with much smaller increases in DU in order to have the terrestrial K and U abundances at chondritic levels. In addition, if radioactive heating is important for planetary cores, U and Th will be more important than K unless the lower mantle has K/U greater than 10 times chondritic or large changes in partition coefficients with conditions reverse the relative importance of K versus U and Th from our measurements

Extreme Pu-U and Possible Pu-REE Fractionation in Unequilibrated Chondrites

The purpose of this study is to understand actinide chemistry in chondrites and to evaluate unequilibrated chondrites for either Pu/U or Pu/Nd chronology. Using fission track radiography for Nadiabondi (H5/(Murrell and Burnett, 1982), Dhajala (H3,4), Bremervorde (H3), Sharps (H3), and Tieschitz (H3), we find that U is primarily located in chondrule glass (50-500 ppb, average of ~ 100 ppb). Apatite from the unequilibrated chondrites contains 150-200 ppb U while whitlockite contains < 17 ppb [low compared to type-6 chondrites which have 1-6 ppm U in apatite and ~ 200 ppb in whitlockite (Pellas and Storzer, 1975)]. Nadiabondi phosphates are intermediate (Murrell and Burnett, 1982). These observations suggest that the phosphate U content increases with petrologic type (Pellas and Storzer, 1975), with U obtained from chondrule glass during metamorphism

Antiferromagnetic Exchange Interaction between Electrons on Degenerate LUMOs in Benzene Dianion

We discuss the ground state of Benzene dianion (Bz$^{2-}$) on the basis of the numerical diagonalization method of an effective model of $\pi$ orbitals. It is found that the ground state can be the spin singlet state, and the exchange coupling between LUMOs can be antiferromagnetic.Comment: Accepted for publication in J. Phys. Soc. Jpn., 2 pages, 3 figure

High Cyanobacterial Abundance in Three Northeastern Gulf of Mexico Estuaries

Aquatic phytoplankton comprise a wide variety of taxa spanning more than 2 orders of magnitude in size, yet studies of estuarine phytoplankton often overlook the picoplankton, particularly chroococcoid cyanobacteria (cf. Synechococcus). Three Gulf of Mexico estuaries (Apalachicola Bay, FL; Pensacola Bay, FL; Weeks Bay, AL) were sampled during summer and fall 2001 to quantify cyanobacterial abundance, to examine how cyanobacterial abundance varied with hydrographic and nutrient distributions, and to estimate the contribution of cyanobacteria to the bulk phytoplankton community. Cyanobacterial abundances in all 3 estuaries were high, averaging 0.59 ± 0.76 X 109 L–1 in Apalachicola Bay, 1.7 ± 1.2 X 109 L–1 in Pensacola Bay and 2.4 ± 1.9 X 109 L–1 in Weeks Bay (mean ± standard deviation). Peak abundances typically occurred in the oligohaline zone (low salinity estuarine zone) during the summer. Freshwater sites had nearly undetectable abundances, and marine sites had abundances several-fold lower than the oligohaline zone. When converted to equivalent chlorophyll a concentrations, cyanobacteria comprised a large fraction of the total phytoplankton biomass, at times approaching 100% in all 3 systems. These observations clearly indicate a cyanobacterial community of estuarine origin that can make up a large proportion of phytoplankton biomass