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141.
Genistein inhibits the inward rectifying potassium current in guinea pig ventricular myocytes 总被引:3,自引:0,他引:3
Genistein is an isoflavone with potent inhibitory activity on protein tyrosine kinase. Previous studies have shown that genistein has additional effects, among which the direct blocking effects on various ionic channels have recently been disclosed. Using whole-cell voltage clamp and current clamp techniques, we demonstrate that micromolar concentrations of genistein dose-dependently and reversibly inhibit the inward rectifying K(+) current, and depolarize the resting membrane potential, resulting in abnormal automaticity in guinea pig ventricular myocytes. Interestingly, another potent tyrosine kinase inhibitor, tyrphostin 51, did not produce the same inhibitory effect, while the inactive analogue of genistein, daidzein, had a similar blocking effect. We suggest that genistein directly blocks the inward rectifying K(+) current in ventricular myocytes, and one should be cautious of its pro-arrhythmic effect in clinical use. 相似文献
142.
DNA-based methods for the detection and the identification of phytoplasmas in insect vector extracts
DNA extraction and storage methods have been evaluated with laboratory-reared leafhoppers and/or field-collected leafhoppers
and psyllids. Detection of four different phytopathogenic phytoplasmas, belonging to three taxonomic groups, has been achieved
by several direct or nested polymerase chain reaction (PCR) methods with such DNA extracts. Reactions differed in both the
16/23S ribosomal primer pairs used and the specific assay and cycling conditions. Merits and possible hindrances of the various
primer pairs, in relation to insect DNA extracts, are discussed. However, identification of the phytoplasma(s) necessarily
relied on comparison of the polymorphism in length of the amplified DNA fragments obtained by restriction with appropriate
endonucleases. Endonuclease digestion is crucial for determining the identity (subgroup affiliation) of phytoplasmas of the
same groups that can be carried by an individual vector. 相似文献
143.
Turan B 《Biological trace element research》2003,94(1):49-59
The whole-cell voltage-clamp technique was applied to isolated ventricular myocytes to investigate the effects of extracellular
and intracellular zinc application on L-type Ca2+ channel currents (I
Ca). Extracellular zinc exposure at micromolar concentration induced a reversible (with washout of ZnCl2) reduction (30%) of I
Ca with no change in current-voltage relationship. On the other hand, an increase of intracellular free-zinc concentration,
[Zn2+]i, from normal (less than 1 nM) to approx 7 nM with 10 μM Zn-pyrithione exposure caused an inhibition of 33±6% in the peak of the I
Ca and altered the voltage dependency of L-type Ca2+ channels with a 10-mV left shift and a hump at around −40 mV in its current-voltage relation. In contrast, N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) strongly inhibited the I
Ca (42±2%), with only a small but detectable outward shift of the holding current measured at the end of the pulses. Zn-pyrithione
and TPEN caused a reproducible decrease of the I
Ca. Interestingly, TPEN application, without Zn-pyrithione pretreatment, inhibited the I
Ca (35±2%) with no change in voltage dependency. Taken together, the results suggest that both extracellular and intracellular
zinc increases under pathological conditions in cardiomyocytes can alter the I
Ca, but their effects are not in the same order and same manner. One should consider these possible side effects when it is
suggested to be vital to cardiovascular cell integrity and functions. 相似文献
144.
Residual dipolar couplings (RDCs) observed between nuclear spins in molecules in partially oriented media have become a valuable source of information for NMR spectroscopists seeking to structurally characterize biological macromolecules. Examination of the form of the direct (D) and indirect (J) nuclear spin-spin coupling Hamiltonians indicates that all observed RDCs contain an unknown contribution from the anisotropic part of J (J) in addition to the direct dipolar contribution, D
PQ. Here, we evaluate the influence of J on RDCs through a series of DFT calculations on model peptides. Very small corrections to one-bond RDCs measured between heavy atoms in peptides and proteins are recommended: +0.51% for N-C spin pairs, and +0.45% for C-C spin pairs. The corrections to RDCs involving at least one proton are negligible. This latter point is likely to be equally applicable to nucleic acids and oligosaccharides in addition to peptides and proteins. Finally, the orientations of the J(N, C) and J(C, C) tensors in the molecular framework are reported for glycylglycine. 相似文献
145.
AC voltammetric carbon paste-based enzyme immunosensors 总被引:10,自引:0,他引:10
Fernández-Sánchez C González-García MB Costa-García A 《Biosensors & bioelectronics》2000,14(12):917-924
Carbon paste electrodes, previously anodised in a basic media, are the basis for the development of a new voltammetric immunosensor device. Passive adsorption of the appropriate immunochemical reagent was performed onto the electrode surface. Alkaline Phosphatase labelled immunoglobulin was the tracer used in this work, 3-indoxyl phosphate being a very suitable enzymatic substrate for the electrochemical detection of the corresponding affinity reaction. The hydrolysis of this molecule generates indigo dimmer. This product was detected by alternating current voltammetry taking advantage of the adsorptive and inherent electrodic properties that it exhibits. The same electrochemical anodisation was used at the end of one assay to remove the entire protein layer attached to the carbon paste surface, allowing the formation of a new sensing phase and the use of the same support in several consecutive experiments. The methodology was applied to the design of two different immunoassays for the determination of human IgG. Good reproducibility of the electrodic signal and a limit of detection around 10−10 M were achieved. 相似文献
146.
Dicyclohexylcarbodiimide (DCCD) is a carboxyl group modifier and it is an inhibitor of various ATPases. Present experiments,
using an in vitro preparation, were designed to study whether DCCD affected the transporters of the bullfrog cornea epithelium,
specifically, the Na+/K+ ATPase pump located in the basolateral membrane. For this purpose, corneas were impaled with microelectrodes and experiments
were done under short-circuit current (I
sc
) conditions. Addition of DCCD to a concentration of 10−4
m to the tear solution gave a marked decrease in I
sc
; a marked depolarization of the intracellular potential, V
o
; and a significant decrease in the apical membrane fractional resistance, fR
o
. There were small and variable although significant changes in the transepithelial conductance, g
t
. The effects may be explained by a decrease in the basolateral membrane K+ conductance, in combination with a partial inhibition of the Na+/K+-ATPase pump located in the basolateral membrane. There is also evidence for an increase in the apical membrane Cl− conductance.
Received: 12 August 1999/Revised: 16 November 1999 相似文献
147.
148.
冬小麦原生质体培养的胚状体直接发生 总被引:5,自引:0,他引:5
冬小麦品种“京花一号”胚性愈伤组织在改良的N6培养基(NBD培养基)上继代得到易碎型胚性愈伤组织,转入改良MS液体培养基(MSDL培养基)后得到胚性悬浮系,分离的原生质体在改良的MS培养基(MSDP培养基)上培养,再生细胞直接产生体细胞胚胎,并再生出完整植株。体细胞胚胎形成过程与小麦合子胚的形成过程十分相似。 相似文献
149.
A functional kinetic model is developed to describe the activation gating process of the Shaker potassium channel. The modeling in this paper is constrained by measurements described in the preceding two papers, including macroscopic ionic and gating currents and single channel ionic currents. These data were obtained from the normally activating wild-type channel as well as a mutant channel V2, in which the leucine at position 382 has been mutated to a valine. Different classes of models that incorporate Shaker''s symmetrical tetrameric structure are systematically examined. Many simple gating models are clearly inadequate, but a model that can account for all of the qualitative features of the data has the channel open after its four subunits undergo three transitions in sequence, and two final transitions that reflect the concerted action of the four subunits. In this model, which we call Scheme 3+2′, the channel can also close to several states that are not part of the activation path. Channel opening involves a large total charge movement (10.8 e0), which is distributed among a large number of small steps each with rather small charge movements (between 0.6 and 1.05 e0). The final two transitions are different from earlier steps by having slow backward rates. These steps confer a cooperative mechanism of channel opening at Shaker''s activation voltages. In the context of Scheme 3+2′, significant effects of the V2 mutation are limited to the backward rates of the final two transitions, implying that L382 plays an important role in the conformational stability of the final two states. 相似文献
150.
The outer hair cell (OHC) from the mammalian organ of Corti possesses a bell-shaped voltage-dependent capacitance function.
The nonlinear capacitance reflects the activity of membrane bound voltage sensors associated with membrane motors that control
OHC length. We have studied the effects of the lipophilic ions, tetraphenylborate (TPB−) and tetraphenylphosphonium (TPP+), on nonlinear capacitance and motility of isolated guinea-pig OHCs. Effects on supporting cells were also investigated.
TPB− produced an increase in the peak capacitance (Cm
pk
) and shifted the voltage at peak capacitance (V
pkCm
) to hyperpolarized levels. Washout reversed the effects. Perfusion of 0.4 μm TPB− caused an average increase in Cm
pk
of 16.3 pF and V
pkCm
shift of 13.6 mV. TPP+, on the other hand, only shifted V
pkCm
in the positive direction, with no change in Cm
pk
. The contributions from native OHC and TPB−-induced capacitance were dissected by a double Boltzmann fitting paradigm, and by blocking native OHC capacitance. While
mechanical response studies indicate little effect of TPB− on the motility of OHCs which were in normal condition or treated with salicylate or gadolinium, the voltage at maximum mechanical
gain (V
δ
Lmax
) was shifted in correspondence with native V
pkCm
, and both changed in a concentration-dependent manner. Both TPB−-induced changes in Cm
pk
and V
pkCm
were affected by voltage prepulses and intracellular turgor pressure. TPB− induced a voltage-dependent capacitance in supporting cells whose characteristics were similar to those of the OHC, but no
indication of mechanical responses was noted. Our results indicate that OHC mechanical responses are not simply related to
quantity of nonspecific nonlinear charge moved within the membrane, but to the effects of motility voltage-sensor charge movement
functionally coupled to a mechanical effector.
Received: 14 May 1998/Revised: 24 August 1998 相似文献