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61.
1. The conditions are described which are necessary for the comparison of certain types of electrokinetic potentials. An experimental comparison is made of (a) electrophoresis of quartz particles covered with egg albumin; and (b) similar experiments by Briggs on streaming potentials. A slight, consistent, difference is found between the electrophoretic potential and the streaming potential. This difference is probably due to the difference in the protein preparations used rather than to real difference in the electrophoretic and streaming potentials.
2. Data are given which facilitate the measurements and enhance the precision of the estimation of electrical mobilities of microscopic particles. 相似文献
62.
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64.
Elif ERTÜRK Ferda ARI Ouzhan AKGÜN Engin ULUKAYA Cem smail KÜÜKAL Ümit ZEYBEK 《Turkish Journal of Biology》2021,45(5):613
Understanding of the functions of microRNAs in breast cancer and breast cancer stem cells have been a hope for the development of new molecular targeted therapies. Here, it is aimed to investigate the differences in the expression levels of let-7a, miR-10b, miR-21, miR-125b, miR-145, miR-155, miR-200c, miR-221, miR-222 and miR-335, which associated with gene and proteins in MCF-7 (parental) and MCF-7s (Mammosphere/stem cell-enriched population/CD44+/CD24-cells) cells treated with paclitaxel. MCF-7s were obtained from parental MCF-7 cells. Cytotoxic activity of paclitaxel was determined by ATP assay. Total RNA isolation and cDNA conversion were performed from the samples. Changes in expression levels of miRNAs were examined by RT-qPCR. Identified target genes and proteins of miRNAs were analyzed with RT-qPCR and western blot analysis, respectively. miR-125b was significantly expressed (2.0946-fold; p = 0.021) in MCF-7s cells compared to control after treatment with paclitaxel. Downregulation of SMO, STAT3, NANOG, OCT4, SOX2, ERBB2 and ERBB3 and upregulation of TP53 genes were significant after 48 h treatment in MCF-7s cells. Protein expressions of SOX2, OCT4, SMAD4, SOX2 and OCT4 also decreased. Paclitaxel induces miR-125b expression in MCF-7s cells. Upregulation of miR-125b may be used as a biomarker for the prediction of response to paclitaxel treatment in breast cancer. 相似文献
65.
Robert M. Clancy Steven B. Abramson Chuck Kohne John Rediske 《Journal of cellular physiology》1997,172(2):183-191
Nitric oxide (NO) has been implicated in both cartilage degradation and cell survival. Importantly, NO has been shown, in a cell-type-dependent manner, to directly cause cell death or indirectly promote cell death by compromising the ability of cells to detoxify intra- or extracellular oxidants. In this study we examined the role of NO in the survival of bovine chondrocytes exposed to catabolic cytokines (interleukin-1 (IL-1); tumor necrosis factor [TNF]) with or without the addition of an exogenous oxidant stress (e.g., H2O2, HOOCl, etc.). The exposure of chondrocytes to a mixture of IL-1 and TNF (IL-1/TNF) results in the release of NO but did not alter cell viability. However, there was evidence of NO-dependent oxidative responses in the IL-1/TNF group, as we observed an increased level of intracellular oxidants as well as the appearance of a 55 kD nitrated protein which reflects the formation of peroxynitrite. We next analyzed viability with H2O2. The LD50 for IL-1/TNF-treated cells was 0.1 mM (vs. 1 mM for control). The enhanced sensitivity was completely reversed when cells were incubated with the NO synthase inhibitor 1-n5-1-iminoethylornithine (NIO). To test whether cell death was caused by compromising the ability of cells to detoxify extracellular oxidants, we examined the hexose monophosphate shunt (HMPS) response in cells given H2O2. Treatment of control cells with H2O2 resulted in a fourfold increase in HMPS activity. In contrast, IL-1/TNF cells exhibited no increase in HMPS activity. The attenuation of stimulated HMPS activity was reversed by the coaddition of NIO. Thus, these data indicate that (1) endogenous NO mediates cytokine-dependent susceptibility to oxidant injury and (2) this effect is in part due to impaired activation of the HMPS. In inflamed joints replete with cytokines and oxidants, NO may contribute to chondrocyte death and progressive joint destruction. J. Cell. Physiol. 172:183–191, 1997. © 1997 Wiley-Liss, Inc. 相似文献
66.
Continuous monitoring of phytoplankton dynamics in Lake Balaton (Hungary) using on-line delayed fluorescence excitation spectroscopy 总被引:5,自引:0,他引:5
VERA ISTVÁNOVICS MÁRK HONTI RÁS OSZTOICS HESHAM M. SHAFIK JUDIT PADISÁK YOSSEF YACOBI WERNER ECKERT 《Freshwater Biology》2005,50(12):1950-1970
1. This study introduces delayed fluorescence (DF) excitation spectroscopy as an on‐line tool for in situ monitoring of the composition and biomass of various colour classes of phytoplankton when they are photosynthetically active (cyanobacteria, chlorophytes, chromophytes and cryptophytes). The DF data are validated by comparison with those from conventional methods (weekly microscopic counts and the measurement of chlorophyll concentration). 2. The composition of phytoplankton as assessed by DF agreed reasonably well with the results from microscopic counts, particularly when differences in chlorophyll‐specific DF integrals of the various colour classes were taken into account. 3. Integrals of DF spectra were converted into concentration of chlorophyll a using empirical factors derived from field data. The value of the conversion factor was nearly twice as high when the relative abundance of cyanobacteria was low (<15%) than when it was high. The converted DF‐chl time series agreed well with chlorophyll measurements particularly when blooms were developing. As the DF method is inherently free of the interference caused by pigment degradation products, the discrepancy between the two data sets increased during the collapse of blooms and when sediment resuspension was intense. 4. Fourier spectrum analysis of the time series of DF‐chl indicated that samples must be taken, at a minimum, every 2–3 days to capture the dynamics of phytoplankton. As a consequence, the dynamics of various algal blooms, including their timing, duration and net growth rate, could be estimated with greater confidence than by using conventional methods alone. 5. On‐line DF spectroscopy is an advanced technique for monitoring daily the biomass and composition of the photosynthetically active phytoplankton in aquatic environments, including turbid shallow lakes. At present, the detection limit is around 1 mg DF‐chl a m?3 in terms of total biomass but confidence in estimates of phytoplankton composition declines sharply below about 5 mg chl a m?3. 6. On‐line DF spectroscopy represents a promising approach for monitoring phytoplankton. It will be useful in water management where it can act as an early‐warning system of declines in water quality. In basic ecological research it can supplement manual methods. While default calibration spectra may be acceptable for routine monitoring, we suggest a careful individual calibration of the DF spectrometer for basic research. The statistical methods developed here help to assess the adequacy of various calibration sets. 相似文献
67.
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69.
A Puri R Sethi B Singh SK Dwivedi VS Narain RK Saran VK Puri 《Indian pacing and electrophysiology journal》2009,9(3):186-189
A 25-year-old previously asymptomatic pregnant woman at 36 weeks'' gestation was noticed to have repetitive monomorphic ventricular tachycardia. A dilated left ventricle with moderately reduced systolic function was found on echocardiographic examination. This is a very rare presentation of peripartum cardiomyopathy (PPCMP) presenting with repetitive monomorphic ventricular tachycardia. 相似文献
70.
Vincent Chaptal Michela Ottolia Gabriel Mercado-Besserer Debora A. Nicoll Kenneth D. Philipson Jeff Abramson 《The Journal of biological chemistry》2009,284(22):14688-14692
The mammalian Na+/Ca2+ exchanger, NCX1.1, serves as
the main mechanism for Ca2+ efflux across the sarcolemma following
cardiac contraction. In addition to transporting Ca2+, NCX1.1
activity is also strongly regulated by Ca2+ binding to two
intracellular regulatory domains, CBD1 and CBD2. The structures of both of
these domains have been solved by NMR spectroscopy and x-ray crystallography,
greatly enhancing our understanding of Ca2+ regulation.
Nevertheless, the mechanisms by which Ca2+ regulates the exchanger
remain incompletely understood. The initial NMR study showed that the first
regulatory domain, CBD1, unfolds in the absence of regulatory Ca2+.
It was further demonstrated that a mutation of an acidic residue involved in
Ca2+ binding, E454K, prevents this structural unfolding. A
contradictory result was recently obtained in a second NMR study in which
Ca2+ removal merely triggered local rearrangements of CBD1. To
address this issue, we solved the crystal structure of the E454K-CBD1 mutant
and performed electrophysiological analyses of the full-length exchanger with
mutations at position 454. We show that the lysine substitution replaces the
Ca2+ ion at position 1 of the CBD1 Ca2+ binding site and
participates in a charge compensation mechanism. Electrophysiological analyses
show that mutations of residue Glu-454 have no impact on Ca2+
regulation of NCX1.1. Together, structural and mutational analyses indicate
that only two of the four Ca2+ ions that bind to CBD1 are important
for regulating exchanger activity.Cardiac contraction/relaxation relies upon Ca2+ fluxes across
the plasma membrane (sarcolemma) of cardiomyocytes. Rapid Ca2+
influx (primarily through L-type Ca2+ channels) triggers the
release of additional Ca2+ from the sarcoplasmic reticulum
(SR),4 resulting in
cardiomyocyte contraction. Removal of cytosolic Ca2+ by reuptake
into the SR (through the SR Ca2+-ATPase) and expulsion from the
cell (primarily through the Na+/Ca2+ exchanger, NCX1.1)
results in relaxation (1).
Altered Ca2+ cycling is observed in a number of pathophysiological
situations including ischemia, hypertrophy, and heart failure
(2). Understanding the function
and regulation of NCX1.1 is thus of fundamental importance to understand
cardiac physiology.NCX1.1 utilizes the electrochemical potential of the Na+
gradient to extrude Ca2+ in a ratio of three Na+ ions to
one Ca2+ ion (3). In
addition to transporting both Na+ and Ca2+, NCX1.1 is
also strongly regulated by these two ions. Intracellular Na+ can
induce NCX1.1 to enter an inactivated state, whereas Ca2+ bound to
regulatory sites removes Na+-dependent inactivation and also
activates Na+/Ca2+ exchange
(3). These regulatory sites are
located on a large cytoplasmic loop (∼500 residues located between
transmembrane helices V and VI) containing two calcium binding domains (CBD1
and CBD2), which sense cytosolic Ca2+ levels. We have previously
shown that Ca2+ binding to the primary site in CBD2 is required for
full exchange regulation (4);
CBD1, however, is a site of higher affinity and appears to dominate the
activation of exchange activity by Ca2+.Both CBDs have an immunoglobulin fold formed from two antiparallel β
sheets generating a β sandwich with a differing number of Ca2+
ions coordinated at the tip of the domain
(4,
5). CBD1 binds four
Ca2+ ions, whereas CBD2 binds only two Ca2+ ions. An
initial NMR study revealed a local unfolding of the upper portion of CBD1 upon
release of Ca2+ (6).
In contrast, CBD2 did not display an unfolding response upon Ca2+
removal. A comparative analysis between CBDs revealed a difference in charge
at residues in equivalent positions near the Ca2+ coordination
site; Glu-454 in CBD1 is replaced by Lys-585 in CBD2. The unstructuring of
CBD1 upon Ca2+ removal was alleviated by reversing the charge of
the acidic residue (E454K) involved in Ca2+ coordination
(6). Previously, we solved the
structures of the Ca2+-bound and -free conformations of CBD2 and
revealed a charge compensation mechanism involving Lys-585
(4). The positively charged
lysine residue assumes the position of one of the Ca2+ ions upon
Ca2+ depletion, permitting CBD2 to retain its overall fold
(4). A similar phenomenon is
predicted to take place in E454K-CBD1 mutant. In addition, Hilge et
al. (6) showed that the
E454K mutation of CBD1 decreases Ca2+ affinity to a level similar
to that of CBD2 and suggested that the E454K mutation would cause the loss of
primary regulation of NCX1.1 by CBD1.The significance of some of these observations is unclear as a recent NMR
study (7) of CBD1 under more
physiologically relevant conditions revealed no significant alteration in
tertiary structure in the absence of Ca2+. It was hypothesized that
Ca2+ binding induces localized conformational and dynamic changes
involving several of the binding site residues. To clarify this issue, we
solved the crystal structure of the E454K-CBD1 mutant and examined the
functional effects of different CBD1 mutations in the full-length NCX1.1. The
results indicate that charge compensation is indeed provided by the residue
Lys-454 to replace one Ca2+, whereas the overall E454K-CBD1
structure is only slightly perturbed. The charge compensation, however, has no
impact on Ca2+ regulation of NCX1.1. 相似文献