Penrose limits and Green-Schwarz strings

We discuss the Green-Schwarz action for type IIB strings in general plane-wave backgrounds obtained as Penrose limits from any IIB supergravity solutions with vanishing background fermions. Using the normal-coordinate expansion in superspace, we prove that the light-cone action is necessarily quadratic in the fermionic coordinates. This proof is valid for more general pp-wave backgrounds under certain conditions. We also write down the complete quadratic action for general bosonic on-shell backgrounds in a form in which its geometrical meaning is manifest both in the Einstein and string frames. When the dilaton and 1-form field strength are vanishing, and the other field strengths are constant, our string-frame action reduces, up to conventions, to the one which has been written down using the supercovariant derivative.Comment: 18 pages, latex, no figures; (v2) relation to ref.14 clarified; (v3) typos corrected, minor change

Localized bioconvection of Euglena caused by phototaxis in the lateral direction

Euglena, a swimming micro-organism, exhibited a characteristic bioconvection that was localized at the center of a sealed chamber under bright illumination to induce negative phototaxis. This localized pattern consisted of high-density spots, in which convection was found. These observations were reproduced by a mathematical model that was based on the phototaxis of individual cells in both the vertical and lateral directions. Our results indicate that this convection is maintained by upward swimming, as with general bioconvection, and the localization originates from lateral phototaxis

Different patterns of Ca2+ signals are induced by low compared to high concentrations of P2Y agonists in microglia

Brain-resident macrophages (microglia) are key cellular elements in the preservation of tissue integrity. On the other hand, they can also contribute to the development of pathological events by causing an extensive and inappropriate inflammatory response. A growing number of reports indicate the involvement of nucleotides in the control of microglial functions. With this study on P2Y receptors in rat microglia, we want to contribute to the definition of their expression profile and to the characterisation of their signalling mechanisms leading to Ca2+ movements. Endogenous nucleotides, when applied at a concentration of 100 μM, elicited robust Ca2+ transients, thanks to a panel of metabotropic receptors comprising mainly P2Y2, P2Y6 and P2Y12 subtypes. The involvement of P2Y12 receptors in Ca2+ responses induced by adenine nucleotides was confirmed by the pharmacological and pertussis toxin sensitivity of the response induced by adenosine diphosphate (ADP). Beside the G protein involved, Gi and Gq respectively, adenine and uracil nucleotides differed also for induction by the latter of a capacitative Ca2+ plateau. Moreover, when applied at low (sub-micromolar) concentrations with a long-lasting challenge, uracil nucleotides elicited oscillatory Ca2+ changes with low frequency of occurrence (≤ 1 min−), sometimes superimposed to an extracellular Ca2+-dependent sustained Ca2+ rise. We conclude that different patterns of Ca2+ transients are induced by low (i.e., oscillatory Ca2+ activity) compared to high (i.e., fast release followed by sustained raise) concentrations of nucleotides, which can suggest different roles played by receptor stimulation depending not only on the type but also on the concentration of nucleotides

Modification of neuropathic pain sensation through microglial ATP receptors

Neuropathic pain that typically develops when peripheral nerves are damaged through surgery, bone compression in cancer, diabetes, or infection is a major factor causing impaired quality of life in millions of people worldwide. Recently, there has been a rapidly growing body of evidence indicating that spinal glia play a critical role in the pathogenesis of neuropathic pain. Accumulating findings also indicate that nucleotides play an important role in neuron-glia communication through P2 purinoceptors. Damaged neurons release or leak nucleotides including ATP and UTP to stimulate microglia through P2 purinoceptors expressing on microglia. It was shown in an animal model of neuropathic pain that microglial P2X4 and P2X7 receptors are crucial in pain signaling after peripheral nerve lesion. In this review, we describe the modification of neuropathic pain sensation through microglial P2X4 and P2X7, with the possibility of P2Y6 and P2Y12 involvement

Hypertension Is Associated with Marked Alterations in Sphingolipid Biology: A Potential Role for Ceramide

Background Hypertension is, amongst others, characterized by endothelial dysfunction and vascular remodeling. As sphingolipids have been implicated in both the regulation of vascular contractility and growth, we investigated whether sphingolipid biology is altered in hypertension and whether this is reflected in altered vascular function. Methods and Findings In isolated carotid arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, shifting the ceramide/S1P ratio towards ceramide dominance by administration of a sphingosine kinase inhibitor (dimethylsphingosine) or exogenous application of sphingomyelinase, induced marked endothelium-dependent contractions in SHR vessels (DMS: 1.4±0.4 and SMase: 2.1±0.1 mN/mm; n = 10), that were virtually absent in WKY vessels (DMS: 0.0±0.0 and SMase: 0.6±0.1 mN/mm; n = 9, p Conclusions Hypertension is associated with marked alterations in vascular sphingolipid biology such as elevated ceramide levels and signaling, that contribute to increased vascular tone

Mucin Secretion Induced by Titanium Dioxide Nanoparticles

Nanoparticle (NP) exposure has been closely associated with the exacerbation and pathophysiology of many respiratory diseases such as Chronic Obstructive Pulmonary Disease (COPD) and asthma. Mucus hypersecretion and accumulation in the airway are major clinical manifestations commonly found in these diseases. Among a broad spectrum of NPs, titanium dioxide (TiO2), one of the PM10 components, is widely utilized in the nanoindustry for manufacturing and processing of various commercial products. Although TiO2 NPs have been shown to induce cellular nanotoxicity and emphysema-like symptoms, whether TiO2 NPs can directly induce mucus secretion from airway cells is currently unknown. Herein, we showed that TiO2 NPs (<75 nm) can directly stimulate mucin secretion from human bronchial ChaGo-K1 epithelial cells via a Ca2+ signaling mediated pathway. The amount of mucin secreted was quantified with enzyme-linked lectin assay (ELLA). The corresponding changes in cytosolic Ca2+ concentration were monitored with Rhod-2, a fluorescent Ca2+ dye. We found that TiO2 NP-evoked mucin secretion was a function of increasing intracellular Ca2+ concentration resulting from an extracellular Ca2+ influx via membrane Ca2+ channels and cytosolic ER Ca2+ release. The calcium-induced calcium release (CICR) mechanism played a major role in further amplifying the intracellular Ca2+ signal and in sustaining a cytosolic Ca2+ increase. This study provides a potential mechanistic link between airborne NPs and the pathoetiology of pulmonary diseases involving mucus hypersecretion