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Factors shaping the confocal image of the calcium spark in cardiac muscle cells. 总被引:18,自引:0,他引:18 下载免费PDF全文
The interpretation of confocal line-scan images of local [Ca2+]i transients (such as Ca2+ sparks in cardiac muscle) is complicated by uncertainties in the position of the origin of the Ca2+ spark (relative to the scan line) and by the dynamics of Ca(2+)-dye interactions. An investigation of the effects of these complications modeled the release, diffusion, binding, and uptake of Ca2+ in cardiac cells (producing a theoretical Ca2+ spark) and image formation in a confocal microscope (after measurement of its point-spread function) and simulated line-scan images of a theoretical Ca2+ spark (when it was viewed from all possible positions relative to the scan line). In line-scan images, Ca2+ sparks that arose in a different optical section or with the site of origin displaced laterally from the scan line appeared attenuated, whereas their rise times slowed down only slightly. These results indicate that even if all Ca2+ sparks are perfectly identical events, except for their site of origin, there will be an apparent variation in the amplitude and other characteristics of Ca2+ sparks as measured from confocal line-scan images. The frequency distributions of the kinetic parameters (i.e., peak amplitude, rise time, fall time) of Ca2+ sparks were calculated for repetitive registration of stereotyped Ca2+ sparks in two experimental situations: 1) random position of the scan line relative to possible SR Ca(2+)-release sites and 2) fixed position of the scan line going through a set of possible SR Ca(2+)-release sites. The effects of noise were incorporated into the model, and a visibility function was proposed to account for the subjective factors that may be involved in the evaluation of Ca(2+)-spark image parameters from noisy experimental recordings. The mean value of the resulting amplitude distributions underestimates the brightness of in-focus Ca2+ sparks because large numbers of out-of-focus Ca2+ sparks are detected (as small Ca2+ sparks). The distribution of peak amplitudes may split into more than one subpopulation even when one is viewing stereotyped Ca2+ sparks because of the discrete locations of possible SR Ca(2+)-release sites in mammalian ventricular heart cells. 相似文献
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Polysomes from dark-grown and illuminated barley seedlings were translated in cell-free systems. The translation products reacting with the antibody against the light-harvesting chlorophyll a/b protein (LHCP) were analyzed by polyacrylamide gel electrophoresis. It was found that, in addition to the precursor protein of LHCP, a product was obtained that co-migrated with the mature protein. Furthermore, the results show that the light-induced proly(A)RNA for LHCP is integrated into the polysomal complex without delay, indicating that the integration of LHCP into the membrane is controlled at a higher level of gene expression. 相似文献
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Effects of diethylstilbestrol (DES) on ion fluxes in oat roots (Avena sativa L.) were investigated by measuring K+ and Cl− absorption and K+ efflux. DES rapidly decreased the absorption of K+ (86Rb) and 36Cl− by excised roots; 10−4 molar DES inhibited Cl− absorption in 1 minute and K+ absorption in 1 to 2 minutes. With a 10-minute incubation period, K+ and Cl− absorption were inhibited 50% by 1.1×10−5 molar and 8.4×10−6 molar DES, respectively. Treatment for 3 minutes with 10−4 molar DES caused irreversible inhibition of K+ absorption. Increasing concentrations of KCl in the absorption media decreased the DES inhibition. Experiments with the DES analogs, DES dipropionate, dienestrol and hexestrol, showed that the steric configuration and the hydroxyl group of the DES molecule are important in determining the inhibitory capacity of the compound. 相似文献
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The accuracy of pregnancy diagnosis in swine by rectal palpation and by ultrasound was compared using sows and gilts thirty days or more after breeding. A total of eighty-four pigs were included in this experiment and they were examined an average of thirty-nine days following breeding. Forty-nine animals were slaughtered within a few days of pregnancy examination and thirtyfive were allowed to farrow. Pregnancy status was correctly diagnosed by palpation per rectum in eighty-three of the eighty-four pigs (98.8%) and by ultrasound in eighty-one of the eighty-four pigs (96.6%) examined. The accuracy of the two methods was not significantly different. 相似文献
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ATPase activity of plasma membrane vesicles isolated from oat (Avena sativa L. cv. Goodfield) roots was examined in the presence of various concentrations of MgCl(2) and ATP. A Mg(2+): ATP ratio of about 1 was required for maximal activity regardless of the concentrations used; the optimum concentration for both Mg(2+) and ATP was 9 mm. Based on the ATPase activity at different concentrations of complexed Mg.ATP and free ATP, it is concluded that Mg.ATP is the true substrate of this enzyme.Under certain experimental conditions, high concentrations of MgCl(2) and ATP inhibited the plasma membrane ATPase. On the basis of the relative amounts of free and complexed ATP and Mg(2+), it was found that the different moieties caused different amounts of inhibition. Free ATP inhibited the ATPase at concentrations in excess of 2 mm. Mg.ATP concentrations above 11 mm inhibited the enzyme. Free Mg(2+) caused only a slight inhibition of the ATPase.The Km for Mg.ATP was found to vary from 0.64 to 1.24 mm depending on the experimental conditions. This variation is thought to be due to variable amounts of Mg.ATP, which serves as an inhibitor as well as the substrate, and free ATP, which also inhibits the enzyme. 相似文献
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Jeremy Come Yu Xie Michael Naguib Stephen Jesse Sergei V. Kalinin Yury Gogotsi Paul R. C. Kent Nina Balke 《Liver Transplantation》2016,6(9)
Designing sustainable electrodes for next generation energy storage devices relies on the understanding of their fundamental properties at the nanoscale, including the comprehension of ions insertion into the electrode and their interactions with the active material. One consequence of ion storage is the change in the electrode volume resulting in mechanical strain and stress that can strongly affect the cycle life. Therefore, it is important to understand the changes of dimensions and mechanical properties occurring during electrochemical reactions. While the characterization of mechanical properties via macroscopic measurements is well documented, in situ characterization of their evolution has never been achieved at the nanoscale. It is reported here with in situ imaging, combined with density functional theory of the elastic changes of a 2D titanium carbide (Ti3C2Tx) based electrode in direction normal to the basal plane (electrode surface) during alkaline cation intercalation/extraction. 2D carbides, known as MXenes, are promising new materials for supercapacitors and various kinds of batteries, and understanding the coupling between their mechanical and electrochemical properties is therefore necessary. The results show a strong correlation between the cations content and the out‐of‐plane elastic modulus. This strategy enables identifying the preferential intercalation pathways within a single particle, which is important for understanding ionic transport in these materials. 相似文献