共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Tippe 《生物化学与生物物理学报:生物膜》1980,598(1):200-205
Stationary current voltage characteristics and the action potential of single myelinated nerve fibres were measured to examine the effect of (methanol to octanol) on the electrophysiological function of the axon membrane. K+-depolarized membranes show alkanol-dependent shifts of , the membrane transition voltage, whereas in veratridine-depolarized membranes such are not observed. In the latter case, reduce both the stationary Na+ current and the conductivity step between the high- and low-ohmic conductivity state of the membrane. Action potential amplitude, however, is less affected by the alkanols as is the stationary Na+ current. The results are compared with the alkanol-dependent changes of the thermotropic phase transition in phospholipid bilayers. 相似文献
2.
Chlordiazepoxide has been found to be antiarrhythmic . The purpose of the present investigation is to identify the mechanism(s) of such antiarrhythmic activity. In canine heart, chlordiazepoxide effectively depressed the enhanced repetitive discharges in subendocardial Purkinje fibers surviving acute myocardial infarction. Chlordiazepoxide altered the action potential characteristics of Purkinje fiber by shortening the APD50, APD100 and effective refractory period with little effect on the resting membrane potential. The maximal rate of upstroke (dv/dt) was significantly reduced only at 1 × 10?4M and above in Purkinje fibers and the membrane response curve was consistently shifted to the right by chlordiazepoxide. The ventricular muscle was little affected by chlordiazepoxide except for the shortened APD50 and reduced dv/dt. Chlordiazepoxide exerted nerve blocking potency comparable to lidocaine in the crayfish giant axon. Voltage-clamp experiments in squid axon showed that chlordiazepoxide suppressed both components of membrane current, the transient inward sodium current being diminished far greater than the steady-state potassium current. These results demonstrate a direct action on cardiac and axonal membranes which may be partially responsible for the antiarrhythmic activity of this agent. 相似文献
3.
The permeability of the neutral form of tertiary amine local anesthetics across squid axon membranes was studied by utilizing three different experimental methods: (1) narcotic action of axon excitability was measured by monitoring the time derivative of action potential and the results were analyzed in terms of a diffusion reaction equation of local anesthetics to obtain their permeabilities; (2) the influx of local anesthetic into the axon was measured by use of the radioisotope tracer technique; and (3) the desorption rates of the neutral form of local anesthetics from lipid monolayers were measured and the desorption rate was correlated with permeability.The relative permeabilities obtained for procaine, lidocaine and tetracaine by the above three methods were comparable. The order of relative permeabilities was , and had an inverse correlation with the partition coefficients of anesthetics at oil/water phases. Some discussion concerning the concept of permeability is made when the partition coefficient of a permeant molecule is high. 相似文献
4.
D2O-alanine exchange reactions catalyzed by alanine racemase and glutamic pyruvic transminase 总被引:1,自引:0,他引:1
NMR studies in D2O (>90%) reveal that Alanine Racemase (5.1.1.1.) from catalyzes the exchange of the α hydrogen of - and -alanine with D2O. Glutamic Pyruvic Transaminase (2.6.1.2.) and Glutamic Oxaloacetic Transaminase (2.6.1.1.) catalyze the exchange of α and β hydrogens of -alanine. The rates of exchange of α and β hydrogens appear to be of the same order of magnitude. The transaminase catalyzed exchange is enhanced by catalytic amounts of pyruvate. The side chain of -alanine is held more rigidly at the active site of transaminase so that the planar conjugated system can be extended to include the α and β carbons. A generalized mechanism is proposed for the action of pyridoxal phosphate dependent transaminases which extends Braunstein and Snell mechanism to include the structures which contribute to the labilization of β hydrogens of amino acids by the transaminases that have been studied. 相似文献
5.
The mean sodium current, , and the variance of sodium current fluctuations, var, were measured in myelinated nerve during a depolarization to applied from the resting potential () or from a hyperpolarizing holding potential . From and var the relative variations in the number and the conductance γ of sodium channels following changes of the holding potential were calculated. Hyperpolarizing the membrane from to ?28 mV increased by a factor of 3.7, whereas γ decreased by a factor of 0.53. These actions of holding potential on sodium channels develop slowly since 500 ms prepulses to 0 or ?28 mV do not alter the values of and γ. 相似文献
6.
The genesis and transmission of action potentials in epidermal cells of the newt (Cynops pyrrhogaster) embryo were investigated with special reference to cellular differentiation during development. Typical action potentials can be recorded from any of the epidermal cells at Stage 31. These potentials consist of a fast spike (18 msec) followed by a slow component (164 msec). The potential is graded with current intensity, and only the slow component initiates action potentials in adjacent cells and induces a transmission to other cells. The fast spike was found in all epidermal cells throughout the embryonic stages examined (Stages 26–47). The slow potential, however, appears at Stage 28, persists until Stage just before hatching and then disappears at Stage . Electrical recordings from traumatic embryos (embryos without neural crest cells) or from cultured epidermal cell masses isolated from the pregastrula or the ventral region of the neurula, were compared with the intact embryo. No differences were observed in either the form of the action potential or its transmission. Thus these action potentials appear to be derived from epidermal cells, and are not of nervous origin. Evidence suggests that the transient establishment of excitable membranes in epidermal cells during differentiation is closely related to neural cell differentiation. 相似文献
7.
Carlos E. Argaraña Carlos A. Arce Hector S. Barra Ranwel Caputto 《Archives of biochemistry and biophysics》1977,180(2):264-268
In vitro incorporation of [14C]tyrosine into the C-terminal position of the α subunit of tubulin was not affected by 4 mm cycloheximide. This inhibitor of protein synthesis was used for in vivo experiments. The in vivo incorporation of [14C]tyrosine into soluble brain protein of cycloheximide-treated rats was 10% of that of untreated rats. Treatment with vinblastine sulfate of the soluble brain protein showed that the incorporation of [14C]tyrosine into tubulin was higher in cycloheximide-treated than in untreated rats with respect to the incorporation into the total soluble protein. In the case of cycloheximide-treated rats, about 60% of the radioactivity incorporated into protein was released by the action of carboxypeptidase A, whereas 10% was liberated from the protein of untreated rats. The radioactive compound released by the action of carboxypeptidase A was identified as [14C]tyrosine. The α and β subunits of tubulin from animals that received [14C]tyrosine were separated by polyacrylamide gel electrophoresis. The radiosactivity ratio of subunits of tubulin from cycloheximide-treated rats was threefold higher than that of untreated rats. When a mixture of [14C]amino acids was injected, the radioactivity ratio of subunits of tubulin was similar for cycloheximide-treated and untreated rats. The results reported are consistent with the assumption that the α subunit of tubulin can be tyrosinated in vivo. 相似文献
8.
M Okuda 《Journal of theoretical biology》1974,48(1):51-73
The field of the randomly connected neural network is approximately formulated by Griffith's equation, regarding the network as being continuous. An integral representation of Griffith's equation is derived. If a relative refractory period can be ignored, it is where X(x, t) corresponds to the firing rate and θ means the threshold of the neural firing, τ the absolute refractory period and v the velocity for the spike potential travelling down the axon. The above equation is formally analogous to Caianiello's equation, but the former describes the more macroscopic behaviour of the neural network than the latter. With the aid of computer simulation, appropriate solutions are successfully obtained.In regions where X = 1, neurones are firing at a high constant rate of (active regions). In regions where X = 0, there is no firing of neurones (resting regions). In the neural net for which , the net is generally a mixture of the active regions and of the resting regions. In the case that a large active region is in contact with a large resting region, the propagation velocity of boundary between the two regions tends to the velocity u given by . This expression of velocity u was deduced from the fact that there exists a solution of the type X(x, t) = 1 (ut ? x) for equation (A). In the case of , the active region grows and in the case of , the resting region grows. A fatigue effect is introduced, for which it is hard for neurones to maintain firing states. In this case an active region of definite width L propagates with constant velocity u′. The dependence of L and u′ on characteristics of neural network and on the fatigue effect is investigated. 相似文献
9.
V Sarantoglou P Imbault J H Weil 《Biochemical and biophysical research communications》1980,93(1):134-140
Two distinct monomers, α and β participate in the structures of diffe ent oligomers of glutamine synthetase (EC 6. 3. 1. 2). In ammonium-limited cultures a tetrameric form composed mainly of α monomers was found. In excess of nitrogen an octameric form composed mainly from β monomers is the predominant oligomeric state. The presence of both monomers was observed in intermediate oligomeric forms. 相似文献
10.
Fourier analysis of sequences along edges of the type I collagen molecule constructed from two α1(I) and one α2 chains shows that the molecule is two-sided if the supercoil pitch of the α chains along the molecular axis, P, is 39 residues (, where D = 234 residues or 67 nm). One side has alternating charged and hydrophobic regions with spacings of , while the other side has an excess of hydrophobic residues with a spacing of . These characteristics arise from sequence regularities in the α chains and the geometric relationship between the chains. The pattern is marginally strongest with α2 as chain 1. The sides could form the inside of a helical microfibril where contacts between molecules would fall P apart along the α chains. The sides could form the outside of the microfibril where contacts between microfibrils would be spaced apart by the α chain supercoil along the microfibril axis, P′. If the microfibril is a 54 helix of D-staggered collagen molecules with a left-handed supercoil of pitch , P′ is close to (43 residues). subsets in the α chains give rise to the spacing along the molecule. The microfibril has 41 screw symmetry satisfying X-ray diffraction evidence that microfibrils pack in a tetragonal unit cell.This model is the same as proposed previously by us (Trus & Piez, 1976: Piez & Trus, 1977) except that P = 39 rather than 30 residues. Contrary to our earlier assumption, P = 39 residues is within the range allowed by X-ray diffraction measurements. The present results favor P = 39 since it relates regularities in the α chain sequences to helical parameters in a direct way. Furthermore, model studies show that geometric arguments which support P = 30 are equally strong at P = 39 residues. 相似文献
11.
Peter Gräber 《Biochemical and biophysical research communications》1980,96(3):1232-1239
The accelerated decay of the transmembrane electric field under phosphorylating conditions as well as the concomitant generation of [32P]-ATP after excitation with flash groups has been measured. An acceleration of the decay and a corresponding synthesis of ATP is found on addition of ADP and 1,N6-etheno-ADP (?-ADP). Both effects are smaller in the presence of optimal concentrations of ?-ADP than in the presence of an optimal ADP concentration. A quantitative evaluation of ratio under comparable conditions gives values of 3.3 for ADP and 3.5 for ?-ADP. The results are consistent with the interpretation that the accelerated decay of the transmembrane field is caused directly by a proton flux via the ATPase. 相似文献
12.
Quadrupolar echo deuterium magnetic resonance spectroscopy is used to study the hydrocarbon chain disorder in a 70% potassium palmitate-30% water mixture. The C-D bond order parameters are measured as a function of temperature and position along the chain. In the liquid crystalline, Lα, phase the C-D bond order parameters of the methylene segments near the polar head group are found to increase with increasing temperature to a maximum at about 100°C and then decrease on further increasing the temperature. The order parameters for the remaining methylenes and the methyl group decrease monotonically with increasing temperature. The C–D bond order parameter for the α position undergoes a discontinuous change at and, in fact, for a 10°C range two resolvable splittings are observed for the α posittion. The low temperature, coagel, phase gives a well resolved spectrum where all methylenes are equivalent yielding a value of 168 kHz for e2qQ/h, the quadrupole coupling constant. 相似文献
13.
S D Dunn 《Biochemical and biophysical research communications》1978,82(2):596-602
ATPase activity was restored to the inactive coupling factor, F1ATPase, of strain AN120 () by reconstitution of the dissociated complex with an excess of wild-type α subunit. Large excesses of α gave the highest levels of activity. The other subunits which are required for the reconstitution of ATPase activity, β and γ, did not complement the mutant enzyme. These results indicate that the α polypeptide of the AN120 ATPase is defective. 相似文献
14.
Cathinone and d-norpseudoephedrine are closely related phenylalkylamines isolated from (khat), a plant much abused for its stimulant properties. We have compared the potency of these two compounds on an operant behavioral procedure in rats. Both suppress fixed ratio 20 responding for food in a dose related manner. Cathinone was 7–10 times more potent and had a more rapid onset of action than d-norpseudoephedrine, although the duration of action of cathinone was shorter. The ability of these two compounds to produce amphetamine-like stereotyped movements was in concordance with this same relative potency and difference in duration of action. Comparison of the behavioral effects in rats with the pattern of stimulation reported for khat use by man suggests that cathinone may be the major CNS active component of . 相似文献
15.
Peter J. Natale Carrie Ireland John M. Buchanan 《Biochemical and biophysical research communications》1975,66(4):1287-1293
Messenger RNA for two T4 specific enzymes, deoxynucleotide kinase and α glucosyltransferase, have been sized by sedimentation on sucrose density gradients. The sedimentation constants of transferase and kinase mRNAs formed were 21.5S and 14.5S respectively, regardless of the duration of incubation up to 20 min. Although the kinase mRNA isolated from cells infected with T4 phage for 10 min was the same size as found (14.5S), the transferase mRNA was found in a segment approximating the size of the kinase mRNA (14.5S). The experiments indicate that α glucosyltransferase mRNA is formed first as a polycistronic message and is then processed to the smaller unit. 相似文献
16.
C G Wilde S Boguslawski L L Houston 《Biochemical and biophysical research communications》1979,91(3):1082-1088
The protozoan was found to be resistant to the toxic action of ricin . Isolated ribosomes were strongly resistant to the A subunit of ricin when tested in a cell free protein synthesis system under different conditions and also lacked the ability to bind A chain stoichometrically. This suggests that is resistant because it contains a ribosome which is not susceptible to the toxic action of ricin. 相似文献
17.
Kazuo Yoshida Michio Hagiya Naohiko Yanagishima 《Biochemical and biophysical research communications》1976,71(4):1085-1094
The substance responsible for the sexual agglutinability was successfully solubilized by a newly established autoclaving method from the surface of mating type cells of and purified by DEAE cellulose chromatography, gel filtration, affinity chromatography and electrophoresis. The substance was found to consist of at least two different glycoprotein subunits. The molecular weight of the substance was estimated to be about 23,000 daltons by gel filtration. The substance was univalent in its biological activity and specifically masked the sexual agglutinability of the mating type α cells. The substance formed a complementary complex with the agglutination substance from α cells in vitro. 相似文献
18.
Ilkka Kouvonen 《生物化学与生物物理学报:生物膜》1981,646(2):268-274
The pig intestinal intrinsic factor receptor has been isolated and dissociated into its α and β subunits. The β subunit was found to be more hydrophobic than the α subunit. In a detergent solution only the α subunit was accessible to digestion with papain. The whole isolated receptor was introduced into artificial single bilayer liposomes where is apparently was randomly oriented. Liposomes containing the receptor were digested with papain and the polypeptide segments that stayed in the lipid fraction were extracted and analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Four species were found with values of 23 000, 45 000, 70 000 and 86 000. 相似文献
19.
Effects of different local anesthetics of sodium permeability were studied in single nerve fibres of frog by the method of voltage clamp. Inhibition of sodium current by externally applied tertiary anesthetics, procaine and trimecaine, was the sum of a potentially independent block (reduced ) and slow sodium inactivation with time constants ranging from tens to hundreds of ms depending on membrane potential (at room temperature). Externally applied uncharged benzocaine produced a potentially independent block only. According to dose-response curves both processes are one-to-one reactions. In the case of trimecaine equilibrium constant the reaction responsible for reduction of is about 0.3 mM, while that for slow inactivation is more than ten times less (0.02 mM). Increasing pH from 5.6 to 8.5 markedly accelerated the slow inactivation process at all potential values. Divalent cations Ca2+ and Ni2+ shifted the steady-state slow inactivation curve along the potential axis and simultaneously reduced slow inactivation at the saturation level. Permanently charged quaternary trimecaine was ineffective when applied externally. Internally applied tertiary anesthetics and quaternary trimecaine as well as externally applied quaternary derivative of lidocaine QX-572 produced a progressively irreversible block enhanced by depolarization and inhibition reversibly increased by repetitive short-term depolarization (frequency-dependent inhibition). Inhibition of sodium currents by repetitive stimulation observed also in the case of externally applied tertiary anesthetics is due mainly to slow inactivation. The data suggests the existence of several types of receptor sites through which local anesthetics exert their blocking action on sodium permeability. 相似文献
20.
F Couraud H Rochat S Lissitzky 《Biochemical and biophysical research communications》1978,83(4):1525-1530
The protein neurotoxin II from the venom of the scorpion Hector was labeled with 125I by the lactoperoxidase method to a specific radioactivity of about 100 μCi/μg without loss of biological activity. The labeled neurotoxin binds specifically to a single class of non intereacting binding sites of high affinity (KD = 0.3 – 0.6 nM) and low capacity (4000 – 8000 sites/cell) to electrically excitable neuroblastoma cells. Relation of these sites to the action potential Na+ channel is derived from identical concentration dependence of scorpion toxin binding and increase in duration and amplitude of action potential. The protein neurotoxin II from the sea anemone also affects the closing of the action potential Na+ ionophore in nerve axons. The unlabelled sea anemone toxin modifies 125I-labeled scorpion toxin II binding to neuroblastoma cells by increasing the apparent KD for labeled scorpion toxin without modification of the number of binding sites. It is concluded that both scorpion toxin II and sea anemone toxin II interact competitively with a regulatory component of the action potential Na+ channel. 相似文献