Mkn 463 field observed by BeppoSAX

In this work we present the observation of the Mkn 463 field performed with the MECS instrument on-board BeppoSAX in the 1.8-10.5 keV band. The Mkn 463 field is an example of an extragalactic field crowded with absorbed X-ray sources: apart from the Seyfert 2 galaxy Mkn 463 and the well known QSO PG 1352+183 (the only object showing no absorption), two other objects are detected with a column density in excess to the galactic value. The first 1SAX J1353.9+1820 is a red QSO from the BeppoSAX High Energy Large Area Survey (HELLAS). The second 1SAX J1355.4+1815 is optically unidentified, but its X-ray spectral characteristics indicate that it too is an AGN hidden behind a large column density.Comment: 5 pages, 3 PostScript figures, LaTeX manuscript, new A&A file style included, accepted for publication on Astronomy and Astrophysic

Inhibition of the sarcoplasmic reticulum Ca2+ pump with thapsigargin to estimate the contribution of Na+-Ca2+ exchange to ventricular myocyte relaxation

FAPESP – FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULORelaxation in the mammalian ventricle is initiated by Ca2+ removal from the cytosol, which is performed by three main transport systems: sarcoplasmic reticulum Ca2+-ATPase (SR-A), Na+-Ca2+ exchanger (NCX) and the so-called slow mechanisms (sarcolemmal Ca2+-ATPase and mitochondrial Ca2+ uptake). To estimate the relative contribution of each system to twitch relaxation, SR Ca2+ accumulation must be selectively inhibited, usually by the application of high caffeine concentrations. However, caffeine has been reported to often cause changes in membrane potential due to NCX-generated inward current, which compromises the reliability of its use. In the present study, we estimated integrated Ca2+ fluxes carried by SR-A, NCX and slow mechanisms during twitch relaxation, and compared the results when using caffeine application (Cf-NT) and an electrically evoked twitch after inhibition of SR-A with thapsigargin (TG-TW). Ca2+ transients were measured in 20 isolated adult rat ventricular myocytes with indo-1. For transients in which one or more transporters were inhibited, Ca2+ fluxes were estimated from the measured free Ca2+ concentration and myocardial Ca2+ buffering characteristics. NCX-mediated integrated Ca2+ flux was significantly higher with TG-TW than with Cf-NT (12 vs 7 µM), whereas SR-dependent flux was lower with TG-TW (77 vs 81 µM). The relative participations of NCX (12.5 vs 8% with TG-TW and Cf-NT, respectively) and SR-A (85 vs 89.5% with TG-TW and Cf-NT, respectively) in total relaxation-associated Ca2+ flux were also significantly different. We thus propose TG-TW as a reliable alternative to estimate NCX contribution to twitch relaxation in this kind of analysis.Relaxation in the mammalian ventricle is initiated by Ca2+ removal from the cytosol, which is performed by three main transport systems: sarcoplasmic reticulum Ca2+-ATPase (SR-A), Na+-Ca2+ exchanger (NCX) and the so-called slow mechanisms (sarcolemmal Ca2+-ATPase and mitochondrial Ca2+ uptake). To estimate the relative contribution of each system to twitch relaxation, SR Ca2+ accumulation must be selectively inhibited, usually by the application of high caffeine concentrations. However, caffeine has been reported to often cause changes in membrane potential due to NCX-generated inward current, which compromises the reliability of its use. In the present study, we estimated integrated Ca2+ fluxes carried by SR-A, NCX and slow mechanisms during twitch relaxation, and compared the results when using caffeine application (Cf-NT) and an electrically evoked twitch after inhibition of SR-A with thapsigargin (TG-TW). Ca2+ transients were measured in 20 isolated adult rat ventricular myocytes with indo-1. For transients in which one or more transporters were inhibited, Ca2+ fluxes were estimated from the measured free Ca2+ concentration and myocardial Ca2+ buffering characteristics. NCX-mediated integrated Ca2+ flux was significantly higher with TG-TW than with Cf-NT (12 vs 7 µM), whereas SR-dependent flux was lower with TG-TW (77 vs 81 µM). The relative participations of NCX (12.5 vs 8% with TG-TW and Cf-NT, respectively) and SR-A (85 vs 89.5% with TG-TW and Cf-NT, respectively) in total relaxation-associated Ca2+ flux were also significantly different. We thus propose TG-TW as a reliable alternative to estimate NCX contribution to twitch relaxation in this kind of analysis361217171723FAPESP – FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP – FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO95/0355-

Limits on the Doppler factor in relativistic jets by means of gamma-ray observations

A new, simple and potentially useful method for constraining the kinematical parameters of relativistic jets based on gamma ray spectral measurements of Active Galaxies is presented. The application of this method to the Quasar 3C273 leads to a value of the Doppler factor of 3 to 4. This corresponds to jet parameters of mu 2 and theta 15 deg in good agreement with the values estimated independently from radio observations of superluminal motion. For the particular case of 3C273, the results are also compared to those given by a similar technique based on the comparison of the X-ray observational data with the synchrotron self Compton prediction from radio measurements. The application of the proposed technique to a significant sample of active galaxies as a result of future gamma ray surveys of the sky is briefly discussed, particularly with respect to possible ways to constrain the cosmological constants H sub o and q sub o

Inhibition Of The Sarcoplasmic Reticulum Ca2+ Pump With Thapsigargin Estimate The Contribution Of Na+-ca2+ Exchange To Ventricular Myocyte Relaxation

Relaxation in the mammalian ventricle is initiated by Ca2+ removal from the cytosol, which is performed by three main transport systems: sarcoplasmic reticulum Ca2+-ATPase (SR-A), Na+-Ca2+ exchanger (NCX) and the so-called slow mechanisms (sarcolemmal Ca2+-ATPase and mitochondrial Ca2+ uptake). To estimate the relative contribution of each system to twitch relaxation, SR Ca2+ accumulation must be selectively inhibited, usually by the application of high caffeine concentrations. However, caffeine has been reported to often cause changes in membrane potential due to NCX-generated inward current, which compromises the reliability of its use. In the present study, we estimated integrated Ca2+ fluxes carried by SR-A, NCX and slow mechanisms during twitch relaxation, and compared the results when using caffeine application (Cf-NT) and an electrically evoked twitch after inhibition of SR-A with thapsigargin (TG-TW). Ca2+ transients were measured in 20 isolated adult rat ventricular myocytes with indo-1. For transients in which one or more transporters were inhibited, Ca2+ fluxes were estimated from the measured free Ca2+ concentration and myocardial Ca2+ buffering characteristics. NCX-mediated integrated Ca2+ flux was significantly higher with TG-TW than with Cf-NT (12 vs 7 μM), whereas SR-dependent flux was lower with TG-TW (77 vs 81 μM). The relative participations of NCX (12.5 vs 8% with TG-TW and Cf-NT, respectively) and SR-A (85 vs 89.5% with TG-TW and Cf-NT, respectively) in total relaxation-associated Ca2+ flux were also significantly different. We thus propose TG-TW as a reliable alternative to estimate NCX contribution to twitch relaxation in this kind of analysis.361217171723Bers, D.M., Bassani, J.W.M., Bassani, R.A., Na/Ca exchange and Ca fluxes during contraction and relaxation in mammalian ventricular muscle (1996) Annals of the New York Academy of Sciences, 779, pp. 430-442Bers, D.M., (2001) Excitation-Contraction Coupling and Cardiac Contractile Force, , 2nd edn. Kluwer Press, Dordrecht, The NetherlandsBassani, J.W.M., Bassani, R.A., Bers, D.M., Relaxation in rabbit and rat cardiac cells: Species-dependent differences in cellular mechanisms (1994) Journal of Physiology, 476, pp. 279-293Bassani, R.A., Bassani, J.W.M., Bers, D.M., Relaxation in ferret ventricular myocytes: Unusual interplay among calcium transport systems (1994) Journal of Physiology, 476, pp. 295-308Negretti, N., O'Neill, S.C., Eisner, D.A., The relative contributions of different intracellular and sarcolemmal systems to relaxation in rat ventricular myocytes (1993) Cardiovascular Research, 27, pp. 1826-1830Rousseau, E., Meissner, G., Single cardiac sarcoplasmic reticulum Ca2+-release channel: Activation by caffeine (1989) American Journal of Physiology, 256, pp. H328-H333Bassani, R.A., Bassani, J.W.M., Contribution of Ca2+ transporters to relaxation in intact ventricular myocytes from developing rats (2002) American Journal of Physiology, 282, pp. H2406-H2413Li, L., Chu, G., Kranias, E.G., Bers, D.M., Cardiac myocyte calcium transport in phospholamban knockout mouse: Relaxation and endogenous CaMKII (1998) American Journal of Physiology, 274, pp. H1335-H1347McCall, E., Ginsburg, K.S., Bassani, R.A., Shannon, T.S., Qi, M., Samarel, A.M., Bers, D.M., Ca flux, contractility, and excitation-contraction coupling in hypertrophic rat ventricular myocytes (1998) American Journal of Physiology, 274, pp. H1348-H1360Blaustein, M., Lederer, W.J., Sodium/calcium exchange: Its physiological implications (1999) Physiological Reviews, 79, pp. 763-854Zaniboni, M., Yao, A., Barry, W.H., Musso, E., Spitzer, K., Complications associated with rapid caffeine application to cardiac myocytes that are not voltage-clamped (1998) Journal of Molecular and Cellular Cardiology, 30, pp. 2229-2235Schlotthauer, K., Bers, D.M., Sarcoplasmic reticulum Ca2+ release causes myocyte depolarization: Underlying mechanism and threshold for triggered action potentials (2000) Circulation Research, 87, pp. 774-780Varro, A., Negretti, N., Hester, S.B., Eisner, D.A., An estimate of the calcium content of the sarcoplasmic reticulum in rat ventricular myocytes (1993) Pflügers Archives, 423, pp. 158-160Grynkiewicz, C., Poenie, M., Tsien, R.Y., A new generation of Ca2+ indicators with greatly improved fluorescence properties (1985) Journal of Biological Chemistry, 260, pp. 3440-3450Gomes, P.A.P., Bassani, R.A., Bassani, J.W.M., Measuring [Ca2+] with fluorescent indicators: Theoretical approach to the ratio method (1998) Cell Calcium, 24, pp. 17-26Bassani, J.W.M., Bassani, R.A., Bers, D.M., A method for calibration of indo-1 and resting [Ca]i in intact rabbit cardiac myocytes (1995) Biophysical Journal, 68, pp. 1453-1460Bassani, J.W.M., Bassani, R.A., Bers, D.M., Twitch-dependent SR Ca accumulation and release in rabbit ventricular myocytes (1993) American Journal of Physiology, 265, pp. C533-C540Kirby, M.S., Sagara, Y., Gaa, S., Inesi, G., Lederer, W.J., Rogers, T.B., Thapsigargin inhibits contraction and Ca transient in cardiac cells by specific inhibition of the sarcoplasmic reticulum calcium pump (1991) Journal of Biological Chemistry, 267, pp. 12545-12551Bassani, R.A., Shannon, T.S., Bers, D.M., Passive Ca2+ binding in ventricular myocardium of neonatal and adult rats (1998) Cell Calcium, 23, pp. 433-442Pogwizd, S.M., Qi, M., Yuan, W., Samarel, A.M., Bers, D.M., Upregulation of Na+/Ca2+ exchange expression and function in an arrhythmogenic rabbit model of heart failure (1999) Circulation Research, 85, pp. 1009-101

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles