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1.
V. A. Maltsev H. N. Sabbah M. Tanimura M. Lesch S. Goldstein A. I. Undrovinas 《Cellular and molecular life sciences : CMLS》1998,54(6):597-605
Abnormalities of contractile function have been identified in cardiomyocytes isolated from failed human hearts and from hearts
of animals with experimentally induced heart failure (HF). The mechanism(s) responsible for these functional abnormalities
are not fully understood. In the present study, we examined the relationship between action potential duration, pattern of
contraction and relaxation, and associated intracellular Ca2+ transients in single cardiomyocytes isolated from the left ventricle (LV) of dogs (n = 7) with HF produced by multiple sequential intracoronary microembolizations. Comparisons were made with LV cardiomyocytes
isolated from normal dogs. Action potentials were measured in isolated LV cardiomyocytes by perforated patch clamp, Ca2+ transients by fluo 3 probe fluorescence, and cardiomyocyte contraction and relaxation by edge movement detector. HF cardiomyocytes
exhibited an abnormal pattern of contraction and relaxation characterized by an attenuated initial twitch (spike) followed
by a sustained contracture ('dome') of 1 to 8 s in duration and subsequent delayed relaxation. This pattern was more prominent
at low stimulation rates (58% at 0.2 Hz, n = 211, 21% at 0.5 Hz, n = 185). Measurements of Ca2+ transients in HF cardiomyocytes at 0.2 Hz manifested a similar spike and dome configuration. The dome phase of both the contraction/relaxation
pattern and Ca2+ transients seen in HF cardiomyocytes coincided with a sustained plateau of the action potential. Shortening of the action
potential duration by administration of saxitoxin (100 nM) or lidocaine (30 μM) reduced the duration of the dome phase of
both the contraction/relaxation profile as well as that of the Ca2+ transient profile. An increase of stimulation rate up to 1 Hz caused shortening of the action potential and disappearance
of the spike-dome profile in the majority of HF cardiomyocytes. In HF cardiomyocytes, the action potential and Ca2+ transient duration were not significantly different from those measured in normal cells. However, the contraction-relaxation
cycle was significantly longer in HF cells (314 ± 67 ms, n = 21, vs. 221 ± 38 ms, n = 46, mean ± SD), indicating impaired excitation-contraction uncou pling in HF cardiomyocytes. The results show that, in
cardiomyocytes isolated from dogs with HF, contractile abnormalities and abnormalities of intracellular Ca2+ transients at low stimulation rates are characterized by a spike-dome configuration. This abnormal pattern appears to result
from prolongation of the action potential.
Received 22 January 1998; received after revision 16 March 1998; accepted 27 March 1998 相似文献
2.
C. M. Vázquez R. Coleto R. Zanetti V. Ruiz-Gutierrez 《Cellular and molecular life sciences : CMLS》1997,53(5):442-446
In the present study, we have examined the intestinal Na+ transport, through the Na+-H+ exchanger, in ileal brush-border membrane vesicles (BBMV) isolated from spontaneously hypertensive rats (SHR), and normotensive
Wistar Kyoto (WKY) rats as a control group. Na+ uptake into ileal BBMV was stimulated in the presence of a proton gradient (pH 5.5 inside/pH 7.5 outside) in SHR and WKY
rats, resulting in a transient accumulation (overshoot) in both groups of rats. No overshoot was observed in the absence of
a pH gradient. The magnitude of the accumulation was significantly higher in SHR than in WKY rats. Uptake of Na+ at equilibrium was identical in the presence and the absence of a proton gradient and was not changed in SHR. The use of
amiloride inhibited pH gradient-driven Na+ uptake in a dose-dependent manner with a Ki of 90 μM and 100 μM for SHR and WKY rats, respectively. The relationship between
proton gradient-driven Na+ uptake and external Na+ concentration was saturable and conformed to Michaelis-Menten kinetics in both SHR and WKY rats. Lineweaver-Burk analysis
of the pH gradient-driven Na+ uptake indicated values of Vmax that were significantly increased in SHR compared to WKY rats (11.4±0.55 nmol/mg/8 s vs. 4.96±0.78 nmol/mg/8 s for SHR and
WKY rats, respectively). In contrast, similar Km values for Na+ were found between SHR and WKY rats (4.0±0.2 mM vs. 4.9±0.6 mM for SHR and WKY rats, respectively). These studies show derangement
in ileal BBMV Na+ transport of SHR, which is characterized by increased Na+-H+ exchanger activity.
Received 18 December 1996; received after revision 3 February 1997; accepted 7 February 1997 相似文献
3.
Repolarization abnormalities in cardiomyocytes of dogs with chronic heart failure: role of sustained inward current 总被引:8,自引:0,他引:8
We previously showed that a canine model of chronic heart failure (HF) produced by multiple coronary microembolizations manifests ventricular arrhythmias similar to those observed in patients with chronic HF. In the present study, we used single canine cardiomyocytes isolated from the left ventricle (LV) of normal dogs (n = 13) and dogs with HF (n = 15) to examine the cellular substrate of these arrhythmias. Action potentials (APs) and ion currents were measured by perforated and whole cell patch clamp, respectively. We found prolonged APs and alterations of AP duration resulting in early afterdepolarizations (EADs) at the low pacing rates of 0.5 Hz and 0.2 Hz. Na+ channel blockers saxitoxin (STX, 100 nM) and lidocaine (90 microM) reduced AP duration dispersion and abolished EADs in HF cardiomyocytes. The steady-state current (Iss)-voltage relation, in the voltage range from -25 mV to 25 mV analogous to the AP plateau level, was significantly shifted inward in HF cardiomyocytes. STX and lidocaine shifted the Iss-voltage relationship in an outward direction. The shifts produced by both drugs was significantly greater in cardiomyocytes of dogs with HF, indicating an increase in inward current. In the experimental configuration in which K+ currents were blocked, the density of the steady-state Ca2+ current (ICa) was found to decrease in HF cardiomyocytes by approximately 33%. In contrast, the density of the steady-state Na+ current (INa) significantly (P < 0.01) increased in HF cardiomyocytes (0.17 +/- 0.06 pA/pF) compared with normal cells (0.08 +/- 0.02 pA/pF). The relative contribution of INa to the net inward current was greater in HF cardiomyocytes, as evident from the increased ratio of INa/ICa (from 0.22 to 0.68). These observation support a hypothesis that anomalous repolarization of HF cardiomyocytes is due, at least in part, to an increased steady-state inward Na+ current. 相似文献
4.
A. Zhang T. P.-O. Cheng X. Y. Wu B. T. Altura B. M. Altura 《Cellular and molecular life sciences : CMLS》1997,53(1):69-72
Effects of extracellular magnesium ions ([Mg2+]o ) on intracellular free Mg2+ ([Mg2+]i ) and its subcellular distribution in single fission yeast cells, Schizosaccharomyces pombe, were studied with digital-imaging microscopy and an Mg2+ fluorescent probe (mag-fura-2). Using 0.44 mM [Mg2+]o , [Mg2+]i in yeast cells was 0.91±0.08 mM. Elevation of [Mg2+]o to 1.97 mM induced rapid (within 5 min) increments in [Mg2+]i (2.18±0.11 mM). Lowering [Mg2+]o to 0.06 mM, however, exerted no significant effects on [Mg2+]i (0.93±0.14 mM), at least for periods of up to 30 min. Irrespective of the [Mg2+]o used, the subcellular distribution of [Mg2+]i remained hetero
geneous, i.e. where the sub-plasma membrane region >cytoplasm >nucleus. [Mg2+] in all three subcellular compartments increased significantly, two- to threefold, concomitant with [Mg2+]i when placed in 1.97 mM [Mg2+]o . We conclude that [Mg2+]i in fission yeast is maintained at a physiologic level when [Mg2+]o is low, but intracellular free Mg2+ rapidly rises when [Mg2+]o is elevated. Like most eukaryotic cells, yeast may have a Mg2+ transport system(s) which functions to maintain gradients of Mg2+ from the outside to inside the cell and among its subcellular compartments.
Received 18 April 1996; received after revision 4 July 1996; accepted 26 July 1996 相似文献
5.
Johansson S Gullbo J Lindholm P Ek B Thunberg E Samuelsson G Larsson R Bohlin L Claeson P 《Cellular and molecular life sciences : CMLS》2003,60(1):165-175
Four novel proteins (phoratoxins C–F) have been isolated from the North American mistletoe Phoradendron tomentosum. The amino acid sequences of these phoratoxins were determined unambiguously using a combination of Edman degradation and
trypsin enzymatic digestion, and by electrospray ionization tandem mass spectrometry sequencing. Phoratoxins C, E and F consist
of 46 amino acid residues; and phoratoxin D of 41. All proteins had six cysteines, similar to the earlier described phoratoxins
A and B, which are thionins. The cytotoxicity of each protein was evaluated in a human cell line panel that represented several
cytotoxic drug-resistance mechanisms. For the half-maximal inhibitory concentrations (IC50 values) of the different cell lines in the panel, correlation with those of standard drugs was low. The most potent cytotoxic
phoratoxin C was further tested on primary cultures of human tumor cells from patients. The solid tumor samples from breast
cancer cells were 18 times more sensitive to phoratoxin C than the tested hematological tumor samples.
Received 30 September 2002; received after revision 28 October 2002; accepted 7 November 2002
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6.
G. Meyer G. Bottà G. Fedele D. Cremaschi 《Cellular and molecular life sciences : CMLS》1995,51(11):1045-1051
In intact tissue, [d-Ala2,MePhe4, Gly-ol5] enkephalin (10–5 M;-ligand), diminsihed short-circuit current (Isc) and increased water, Na+ and Cl– net fluxes in vitro under open circuit conditions; it also inhibitedL-valine absorption andL-valine-dependent variations of short-circuit current (Isc, val). Naloxone (10–6 M) antagonized these effects. In the absence of the muscularis and myenteric plexus this enkephalin or morphine (-ligand) reduced Isc and Isc, val. These enkephalin effects occurred at different times. Different concentrations of enkephalin were tested for their effects on Isc, val. [d-Ala2,d-Leu5] enkephalin (mainly a -ligand) significantly decreased Isc but not Isc, val. The reduction ofL-valine absorption does not depend on the effects on basal ion transport. Interaction of opioids with-receptors located in the submucosal plexus and/or in the epithelial cell accounts for this reduction. This enkephalin effect seems to be at least partially under the control of the myenteric plexus. 相似文献
7.
Summary Prostaglandins (PGs) E2, F2, and I2 were examined for their effects on the electrical and mechanical activities of isolated rat, rabbit and guinea-pig hearts. All PGs produced dysrhythmias in rat hearts at low concentrations only, while higher concentrations were antiarrhythmic. Guinea-pig hearts were less responsive while rabbit hearts were completely resistant.We thank the Manitoba Heart Foundation for financial support and Dr J. Pike (Upjohn, Kalamazoo, MI, USA) for gifts of prostaglandins. Dr M. Karmazyn is a Fellow of the Canadian Heart Foundation. 相似文献
8.
We studied the Na+/K+ pump, Na+/K+ ATPase activity, and oxygen consumption (QO2) in hepatocytes isolated from the periportal (PH) and pericentral (CH) regions of the liver lobule, to provide an insight into the functional properties of these cells. Na+/K+ pump activity was determined using86Rb+ (a functional analog of K+) and ouabain, a specific inhibitor of this transport system. Our results indicate the the Na+/K+, pump and Na+/K+ ATPase activity are significantly lower in CH than in PH, although basal ouabain-sensitive (OS) QO2 was negligible in both of these cell preparations. However, OSQO2 was significantly lower in CH than in PH when the Na+/K+ pump was activated using the ionophore nystatin in a Na+-containing medium. These results indicate that the differences in membrane ion transport exist between hepatocytes from different locations of the liver lobule. 相似文献
9.
Briers Y Lavigne R Plessers P Hertveldt K Hanssens I Engelborghs Y Volckaert G 《Cellular and molecular life sciences : CMLS》2006,63(16):1899-1905
The kinetic, thermodynamic and structural stability of gp36C, the virion-associated peptidoglycan hydrolase domain of bacteriophage
ϕKMV, is analyzed. Recombinant gp36C is highly thermoresistant (k = 0.595 h−1 at 95°C), but not thermostable (Tm = 50.2°C, ΔHcal = 6.86 × 104 cal mol−1). However, aggregation influences kinetic stability in an unusual manner since aggregation is more pronounced at 55°C than
at higher temperatures. Furthermore, gp36C reversibly unfolds in a two-state endothermic transition, and circular dichroism
analysis shows that gp36C almost completely refolds after a 3-h heat treatment at 85°C. These properties are in agreement
with gp36C being part of the extensible tail which is ejected in an unfolded state during phage infection.
Received 24 April 2006; received after revision 26 May 2006; accepted 10 June 2006 相似文献
10.
Proteins of thermophilic organisms are adapted to remain well structured and functional at elevated temperatures. Nevertheless
like their 'cousins' that reside at medium temperatures, they require the assistance of molecular chaperones to fold properly
and prevent aggregation. This review compares structural and functional properties of the DnaK/ClpB systems of Thermus thermophilus and, mainly, Escherichia coli (DnakTth and DnakEco). Many elemental properties of these systems remain conserved. However, in addition to a general increase of the thermal
stability of its components, the DnakTth system shows profound differences in its regulation, and genetic as well as oligomeric organization. Whether these differences
are unique or represent general strategies of adaptation to life at elevated temperatures remains to be clarified.
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11.
Watanabe H Nakashima K Saito H Slaytor M 《Cellular and molecular life sciences : CMLS》2002,59(11):1983-1992
An endo-β-1,4-glucanase (EG) was purified from the hindgut of an Australian mound-building termite, Coptotermes lacteus. The hindgut extract had a peak separate from those for extracts obtained from the salivary glands and the midgut based on
sephacryl S-200 gel chromatography, and also demonstrated an origin different from the endogenous EGs of the termite itself.
The recovery was further purified by SDS-PAGE, and its N-terminal amino acid sequence analyzed. This showed high homology
to EGs from glycoside hydrolase family (GHF) 7. PCR-based cloning methods were applied to the hindgut contents of C. lacteus and individual protozoan symbionts from C. formosanus. cDNAs encoding putative EGs homologous to GHF7 members were then identified. The functionality of one of the putative proteins
was confirmed by its expression in Escherichia coli.
Received 18 September 2002; accepted 20 September 2002
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12.
Sampaio MS Bezerra IP Peçanha FL Fonseca PH Capella MA Lopes AG 《Cellular and molecular life sciences : CMLS》2008,65(19):3093-3099
The lack of Na+,K+-ATPase expression in intercalated cells (IC) is an intriguing condition due to its fundamental role in cellular homeostasis.
In order to better understand this question we compared the activities of Na+,K+-ATPase and Na+-ATPase in two MDCK cell clones: the C11, with IC characteristics, and the C7, with principal cells (PC) characteristics.
The Na+,K+-ATPase activity found in C11 cells is far lower than in C7 cells and the expression of its β-subunit is similar in both cells.
On the other hand, a subset of C11 without α-subunit expression has been found. In C11 cells the Na+-ATPase activity is higher than that of the Na+,K+-ATPase, and it is increased by medium alkalinization, suggesting that it could account for the cellular Na+-homeostasis. Although further studies are necessary for a better understanding of these findings, the presence of Na+-ATPase may explain the adequate survival of cells that lack Na+,K+-ATPase.
Received 09 July 2008; received after revision 03 August 2008; accepted 12 August 2008 相似文献
13.
P. Y. D. Wong W. M. Lee A. Y. F. Tsang 《Cellular and molecular life sciences : CMLS》1981,37(1):69-71
Summary The forward motility of the rat caudal epididymal spermatozoa has been studied in different Na+ concentrations. When spermatozoa were suspended in a completely Na+-free solution, the forward motility suffered a progressive fall and after 3 h was completely suppressed. This effect was fully reversible on resuspending the spermatozoa in a solution containing Na+. Amiloride caused a fall in motility and the effect was similar to that of Na+ removal. The inhibition by amiloride of the motility was concentration dependent and the dose response curve showed an IC50-value of about 5×10–5 M. The role of Na+ influx in the maintenance of sperm motility was discussed.This work was supported by the World Health Organization.The technical assistance of Mr C.M. Li and the gift of amiloride from Merck, Sharp and Dohme are gratefully acknowledged. 相似文献
14.
Molecular mechanisms of thrombin function 总被引:9,自引:0,他引:9
The discovery of thrombin as a Na+-dependent allosteric enzyme has revealed a novel strategy for regulating protease activity and specificity. The allosteric
nature of this enzyme influences all its physiologically important interactions and rationalizes a large body of structural
and functional information. For the first time, a coherent mechanistic framework is available for understanding how thrombin
interacts with fibrinogen, thrombomodulin and protein C, and how Na+ binding influences the specificity sites of the enzyme. This information can be used for engineering thrombin mutants with
selective specificity towards protein C and for the rational design of potent active site inhibitors. Thrombin also serves
as a paradigm for allosteric proteases. Elucidation of the molecular basis of the Na+-dependent allosteric regulation of catalytic activity, based on the residue present at position 225, provides unprecedented
insights into the function and evolution of serine proteases. This mechanism represents one of the simplest and most important
structure-function correlations ever reported for enzymes in general. All vitamin K-dependent proteases and some complement
factors are subject to the Na+-dependent regulation discovered for thrombin. Na+ is therefore a key factor in the activation of zymogens in the coagulation and complement systems. 相似文献
15.
Marko Kreft Miha Lukšič Tomaž M. Zorec Mateja Prebil Robert Zorec 《Cellular and molecular life sciences : CMLS》2013,70(8):1483-1492
Astrocytes interact with neurons and endothelial cells and may mediate exchange of metabolites between capillaries and nerve terminals. In the present study, we investigated intracellular glucose diffusion in purified astrocytes after local glucose uptake. We used a fluorescence resonance energy transfer (FRET)-based nano sensor to monitor the time dependence of the intracellular glucose concentration at specific positions within the cell. We observed a delay in onset and kinetics in regions away from the glucose uptake compared with the region where we locally super-fused astrocytes with the d-glucose-rich solution. We propose a mathematical model of glucose diffusion in astrocytes. The analysis showed that after gradual uptake of glucose, the locally increased intracellular glucose concentration is rapidly spread throughout the cytosol with an apparent diffusion coefficient (D app) of (2.38 ± 0.41) × 10?10 m2 s?1 (at 22–24 °C). Considering that the diffusion coefficient of d-glucose in water is D = 6.7 × 10?10 m2 s?1 (at 24 °C), D app determined in astrocytes indicates that the cytosolic tortuosity, which hinders glucose molecules, is approximately three times higher than in aqueous solution. We conclude that the value of D app for glucose measured in purified rat astrocytes is consistent with the view that cytosolic diffusion may allow glucose and glucose metabolites to traverse from the endothelial cells at the blood–brain barrier to neurons and neighboring astrocytes. 相似文献
16.
C. Caravaggi 《Cellular and molecular life sciences : CMLS》1971,27(4):369-371
Riassunto Nessuna influenza sull'attività respiratoria di cellule di fegati e reni di topi è stata notata quando gli animali sono stati trattati con somministrazioni acute o croniche di Na2SeO3. La diminuzione della produzione di14CO2, quando i tessuti degli animali trattati con Na2SeO3 sono stati incubati con14C glucosio, suggerisce la possibilità di un aumento dell'attività catabolica dei lipidi. 相似文献
17.
Summary The quantitative acidimetric investigation (Bjerrum's method) of CuI coordination reactions in homogeneous aqueous medium is feasible by application of the easily accessible, well crystallized stable complex Cu(CH3CN)4ClO4 in 0.1 to 1 molar CH3CN aq., the stability of particles present in the system CuI, CH3CN, H2O being previously established polarographically. The advantage of the new acidimetric method lies in the possibility of investigating CuI in absence of CuII. 相似文献
18.
Bo Xu Shane Waters Caitlin S. Byrt Darren Plett Stephen D. Tyerman Mark Tester Rana Munns Maria Hrmova Matthew Gilliham 《Cellular and molecular life sciences : CMLS》2018,75(6):1133-1144
An important trait associated with the salt tolerance of wheat is the exclusion of sodium ions (Na+) from the shoot. We have previously shown that the sodium transporters TmHKT1;5-A and TaHKT1;5-D, from Triticum monoccocum (Tm) and Triticum aestivum (Ta), are encoded by genes underlying the major shoot Na+-exclusion loci Nax1 and Kna1, respectively. Here, using heterologous expression, we show that the affinity (K m) for the Na+ transport of TmHKT1;5-A, at 2.66 mM, is higher than that of TaHKT1;5-D at 7.50 mM. Through 3D structural modelling, we identify residues D471/a gap and D474/G473 that contribute to this property. We identify four additional mutations in amino acid residues that inhibit the transport activity of TmHKT1;5-A, which are predicted to be the result of an occlusion of the pore. We propose that the underlying transport properties of TmHKT1;5-A and TaHKT1;5-D contribute to their unique ability to improve Na+ exclusion in wheat that leads to an improved salinity tolerance in the field. 相似文献
19.
Microtubule associated protein tau binds to double-stranded but not single-stranded DNA 总被引:3,自引:0,他引:3
Hua Q He RQ Haque N Qu MH del Carmen Alonso A Grundke-Iqbal I Iqbal K 《Cellular and molecular life sciences : CMLS》2003,60(2):413-421
Tau, a major microtubule-associated protein of the neuron, which is known to promote the assembly of and to stabilize microtubules,
has also been seen associated with chromatin in neuronal cell lines, but its role in this subcellular compartment is still
unknown. In this study, the binding of tau to DNA was investigated using the electrophoretic mobility shift assay. Using polynucleotide
as probe, we found that tau bound to double-stranded but not to single-stranded DNA. Formation of tau-polynucleotide complex
was disrupted by alkaline pH and a high concentration of NaCl, but was not affected by dithiothreitol. Electron microscopy
revealed that the protein associated with the nucleic acid in a necklacelike manner. DNA-cellulose chromatography and radioimmunodot-blot
analyses showed that calf thymus histones VI-S, VII-S and VIII-S could replace both recombinant human brain tau352 (tau-23) and tau441 (tau-40) from DNA. Thus, tau appears to bind to DNA reversibly in the presence of histones.
Received 24 November 2002; received after revision 28 December 2002; accepted 30 December 2002
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20.
Adams V Lyras D Farrow KA Rood JI 《Cellular and molecular life sciences : CMLS》2002,59(12):2033-2043
Mobilisable transposons are transposable genetic elements that also encode mobilisation functions but are not in themselves
conjugative. They rely on coresident conjugative elements to facilitate their transfer to recipient cells. Clostridial mobilisable
transposons include Tn4451 and Tn4452 from Clostridium perfringens, and Tn4453a and Tn4453b from Clostridium difficile, all of which are closely related, and Tn5398 from C. difficile. The Tn4451 group of elements encodes resistance to chloramphenicol and is unusual in that transposition is dependent upon a large resolvase
protein rather than a more conventional transposase or integrase. This group of elements also encodes the mobilisation protein
TnpZ that, by acting at the RSA or oriT site located on the transposon, and in the presence of a coresident conjugative element, promotes the movement of the nonreplicating
circular intermediate and
of plasmids on which the transposon resides. The erythromycin resistance element Tn5398 is unique in that it encodes no readily identifiable transposition or mobilisation proteins. However, the element is still
capable of intraspecific transfer between C. difficile isolates, by an unknown mechanism. The detailed analysis of these mobilisable clostridial elements provides evidence that
the evolution and dissemination of antibiotic resistance genes is a complex process that may involve the interaction of genetic
elements with very different properties.
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