Nitric oxide affects sarcoplasmic calcium release in skeletal myotubes.

Item does not contain fulltextIn the present study, we used real-time confocal microscopy to examine the effects of two nitric oxide (NO) donors on acetylcholine (ACh; 10 microM)- and caffeine (10 mM)-induced intracellular calcium concentration ([Ca2+]i) responses in C2C12 mouse skeletal myotubes. We hypothesized that NO reduces [Ca2+]i in activated skeletal myotubes through oxidation of thiols associated with the sarcoplasmic reticulum Ca2+-release channel. Exposure to diethylamine NONOate (DEA-NO) reversibly increased resting [Ca2+]i level and resulted in a dose-dependent reduction in the amplitude of ACh-induced [Ca2+]i responses (25 +/- 7% reduction with 10 microM DEA-NO and 78 +/- 14% reduction with 100 microM DEA-NO). These effects of DEA-NO were partly reversible after subsequent exposure to dithiothreitol (10 mM). Preexposure to DEA-NO (1, 10, and 50 microM) also reduced the amplitude of the caffeine-induced [Ca2+]i response. Similar data were obtained by using the chemically distinct NO donor S-nitroso-N-acetyl-penicillamine (100 microM). These results indicate that NO reduces sarcoplasmic reticulum Ca2+ release in skeletal myotubes, probably by a modification of hyperreactive thiols present on the ryanodine receptor channel

Cytosolic Ca2+ spikes evoked by the thiol reagent thimerosal in both intact and internally perfused single pancreatic acinar cells

Cytosolic calcium signals evoked by the sulphydryl-group-oxidising agent, thimerosal, have been investigated in acutely isolated pancreatic acinar cells. Two techniques were employed for the assessment of the cytosolic free-calcium concentration ([Ca2+]i): measurement of calcium-dependent chloride and non-specific cation currents (whole-cell patch-clamp recording) and microfluorimetry (fura-2). Thimerosal (0.5–100 mgrM) evoked repetitive spikes in both chloride and cation currents as seen by patch-clamp recording, and in [Ca2+]i as seen by microfluorimetry, with a latency of 1–3 min. The response increased in magnitude over time and was not reversed on removal of thimerosal. The thimerosal-induced spikes were reversibly blocked by 2 mM dithiothreitol and by 20 mM caffeine. Inclusion of heparin (200 mgrg/ml) in the pipette solution blocked the thimerosal-induced spikes. The calcium spikes continued after the removal of extracellular calcium; however, low concentrations of thimerosal (0.5–5 mgrM) were unable to initiate a current response in the absence of external calcium. High concentrations of thimerosal (50–100 mgrM) could initiate spikes without extracellular calcium. Thimerosal, at concentrations that failed to produce an independent effect, potentiated the acetylcholine-evoked oscillations in [Ca2+]i. We conclude that thimerosal is able to mobilise calcium from an intracellular store; the blockade by heparin may indicate that thimerosal exerts an action on the inositol trisphosphate pathway. The dependence on extracellular calcium for initiation, but not for continuation of the thimerosal-induced calcium spikes suggests that thimerosal may have the additional effect of inhibiting the plasma membrane calcium ATPase

"Shakespeare's Hypertextual Performances: Remediating The Tempest in Prospero's Books"

Against a multifaceted theoretical background which has investigated the changing cultural contexts of the performances of The Tempest, my paper primarily focuses on Prospero’s Books (1991) by Peter Greenaway. The film mostly raises the issue of the performability of the play in the light of the radical redefinition of the status of textuality, and of the notions of writing/reading and performing space, within the context of what Gunther Kress calls “the new media age” (Kress 2003). The books of Prospero’s library, whose pages are continuously read aloud, quoted and visualized in frames that appear on the screen, often embedded one into another, are not only interactive hypertexts which break the bounds of conventional writing and reading: they also explore the potentialities of a new ‘performing space’ which high-definition digital tools free from the constraints of any physical medium, thus allowing enhanced forms of interaction between word, image, sound and video. In this sense Greenaway addresses the major issue of the ‘performability’ of the text (McGann 1995) in the context of new modes of interaction of different media, which largely respond to Richard Grusin and David Bolter’s notion of ‘remediation’: “a medium is that which remediates. It is that which appropriates the techniques, forms and social significance of other media and attempts to rival or refashion them in the name of the real. A medium in our culture can never operate in isolation, because it must enter into relationships of respect and rivalry with other media. ” (Bolter-Grusin 1999, 98) Against this over-elaborate contamination of media, blending illusion and reality, Sir John Gielgud’s performance of Prospero acquires particular relevance. While enhancing the film’s deliberate cross-identification between Prospero and Shakespeare, the 87 year-old actor increasingly becomes a sort of “third figure in an indivisible trinity” (McMullan: 2008, 157) whose finely enunciated recitation and priest-like stage presence bear echoes of his four precedent performances of the same role for the theatre. Gielgud’s virtuosity as an experienced Shakespearean actor is thus deliberately used to break the cinematic illusion and to reinforce Greenaway’s weaving of codes, media and performing levels