共查询到20条相似文献,搜索用时 15 毫秒
1.
M. W. Ahmed S. Choi K. Lyakhov U. Shaislamov R. K. Mongre D. K. Jeong R. Suresh H. J. Lee 《Plasma Physics Reports》2017,43(3):381-392
Plasma discharge is a novel disinfection and effectual inactivation approach to treat microorganisms in aqueous systems. Inactivation of Gram-negative Escherichia coli (E. coli) by generating high-frequency, high-voltage, oxygen (O2) injected and hydrogen peroxide (H2O2) added discharge in water was achieved. The effect of H2O2 dose and oxygen injection rate on electrical characteristics of discharge and E. coli disinfection has been reported. Microbial log reduction dependent on H2O2 addition with O2 injection was observed. The time variation of the inactivation efficiency quantified by the log reduction of the initial E. coli population on the basis of optical density measurement was reported. The analysis of emission spectrum recorded after discharge occurrence illustrated the formation of oxidant species (OH?, H, and O). Interestingly, the results demonstrated that O2 injected and H2O2 added, underwater plasma discharge had fabulous impact on the E. coli sterilization. The oxygen injection notably reduced the voltage needed for generating breakdown in flowing water and escalated the power of discharge pulses. No impact of hydrogen peroxide addition on breakdown voltage was observed. A significant role of oxidant species in bacterial inactivation also has been identified. Furthermore the E. coli survivability in plasma treated water with oxygen injection and hydrogen peroxide addition drastically reduced to zero. The time course study also showed that the retardant effect on E. coli colony multiplication in plasma treated water was favorable, observed after long time. High-frequency underwater plasma discharge based biological applications is technically relevant and would act as baseline data for the development of novel antibacterial processing strategies. 相似文献
2.
A mathematical model is developed and a numerical analysis is performed for an electric breakdown in a hydrogen-air mixture with a low concentration of H2. It is shown that, at sufficiently low pressures p<10?2 atm, a small molecular-hydrogen additive (η=5×10?5–5×10?3) decreases the reduced field of an electric breakdown in air by a factor of more than 2 because of the appearance of an additional detachment process associated with the chain hydrogen-oxidation reaction. Detailed calculations are performed for the mean number density of negative oxygen ions [O 2 ? ]=103 cm?3 and the hydrogen concentration in air [H2]=0.5, 0.05, and 0.005%. It is found that, for [H2]=0.005%, the breakdown can develop under the action of a geoelectric field of 1.3 V/cm at p?10?4 atm. 相似文献
3.
Oscar A. Candia 《Biophysical journal》1970,10(4):323-344
Excitability (action potential and refractory period) has been described by A. Finkelstein in the depolarizing region of the current-voltage (I-V) curve of the isolated frog skin. Recently Fishman and Macey interpreted this phenomenon as a consequence of a region with negative resistance that confers to the I-V curve an N shape. We have studied the I-V relation of the isolated frog skin in the hyperpolarizing region with a current-ramp system. It was found that in Na2SO4 Ringer's, the resistance continuously increases in the hyperpolarizing direction. When hyperpolarization reaches 300 mv an electrical breakdown occurs, occasionally followed by a region of negative resistance. In NaCl Ringer's the breakdown was also found although the I-V relation was reasonably linear. Unidirectional Na+ outflux was measured at different levels of voltage clamping across the skin and with different Na+ concentrations in the solutions. The Na+ outflux was found to be relatively independent of these parameters. Based on these results a Na+ rectifying structure is postulated. An electrical model for active Na+ transport including a diode and an oscillator is proposed. The effects of CO2, nitrogen, amiloride, and ouabain on the I-V relation are described. 相似文献
4.
A. I. Shishpanov Yu. Z. Ionikh A. V. Meshchanov N. A. Dyatko 《Plasma Physics Reports》2014,40(6):467-480
Results are presented from experimental studies of breakdown and the initial stage of a discharge in a long tube (with an interelectrode distance of 40 cm and a diameter of 2.8 cm) at a pressure of ~1 Torr and pulse discharge current of ~10 mA. Breakdown was produced by positive voltage pulses with a linearly growing leading edge with a steepness of dU/dt ~ 106–108 V/s. The time interval between pulses was varied from τ = 0.5 ms to 1 s, the pulse duration being 10 ms. The work was aimed at studying the memory effect of the discharge gap, namely, the influence of the previous pulse on the breakdown characteristics of the next one. In the experiments, the breakdown voltage was measured at different values of dU/dt and τ. It was found that the memory effect was absent at τ ~ 1 s. At the same time, an increase in the breakdown voltage with increasing dU/dt was observed. In the range of τ ≈ 50–200 ms, the breakdown voltage also did not depend on τ, but the memory effect took place. The memory effect in this case consisted in that the breakdown voltage decreased with increasing dU/dt, so that, at dU/dt ~ 107 V/s, the breakdown voltage was two times lower than in the case of τ ~ 1 s. For τ ~ 1–10 ms, the memory effect manifested itself in that the breakdown voltage depended on τ: it could either decrease (the “normal” effect) or increase (the “anomalous” effect) with increasing τ. Breakdown of the discharge gap was preceded by the propagation of an ionization wave, except for the case of small τ values in the domain of existence of the anomalous effect. Estimates allowing one to qualitatively explain the experimental results are made. 相似文献
5.
Hui Zhang Yan Shang Xuan Wang Hong Zhao Baozhong Han Zesheng Li 《Journal of molecular modeling》2013,19(12):5429-5438
A theoretical investigation is accomplished on the mechanisms of electrical breakdown strength increment of polyethylene at the atomic and molecular levels. It is found that the addition of aromatic carbonyl compounds as voltage stabilizers is one of the important factors for increasing electrical breakdown strength of polyethylene, as the additives can trap hot electrons, obtain energy of hot electrons, and transform the aliphatic cation to relatively stable aromatic cation to prevent the degradation of the polyethylene matrix. The HOMO-LUMO energy gaps (E g), the ionization potentials (IPs), and electron affinities (EAs) at the ground states of a series of aromatic carbonyl compounds are obtained at the B3LYP/6-311+G(d,p) level. The theoretical results are in good agreement with the available experimental findings, show that 2,4-dioctyloxybenzophenone (Bzo) and 4,4'-didodecyloxybenzil (Bd) molecules can effectively increase the electrical breakdown strength when they are doped into polyethylene because of their much smaller E g values than all the other studied aromatic carbonyl molecules and excellent compatibility with polymers matrix. 相似文献
6.
The initiation and characteristics of a low-pressure glow discharge in air in large-diameter discharge tubes are studied. A deviation from the Paschen law is observed: the breakdown curves U dc(pL) shift toward the higher values of U dc and pL as the interelectrode distance L increases. It is shown that the normal regime of a glow discharge is accompanied by gas ionization in the anode sheath. This takes place only for pL values lying to the right of the inflection point in the breakdown curve. The cathode-sheath characteristics in the normal and abnormal regimes of an air discharge for a duralumin cathode are determined. The axial profiles of the ion density, electron temperature, and plasma potential, as well as the anode voltage drop, are measured at various air pressures. 相似文献
7.
The behaviour of lipid bilayer membranes, made of oxidized cholesterol, and UO22+-modified azolectin membranes in a high electric field has been investigated using the voltage clamp method. When a voltage pulse is applied to the membrane of these compositions, the mechanical rupture of the membranes is preceded by a gradual conductance increase which remains quite reversible till a certain moment. The voltage drop at this reversible stage of breakdown leads to a very rapid (characteristic time of less than 5 μs) decrease in the membrane conductance. At repeated voltage pulses of the same amplitude with sufficient intervals between them (approx. 10 s), the current oscillograms reflecting the reversible resistance decrease are well reproduced on the same membrane. The time of attainment of the predetermined level of the membrane conductance is strongly dependent on voltage. At different stages of breakdown we have investigated changes in the conductance of UO22+-modified membrane after the application of two-step voltage pulses, the kinetics of development of the reversible decrease in the membrane resistance in solutions of univalent and divalent ions, and also the influence of sucrose and hemoglobin on the current evolution. The relationship between the reversible conductance increase, the reversible electrical breakdown [15] and the rupture of membrane in an electric field is discussed. We propose the general interpretation of these phenomena, based on the representation of the potential-dependent appearance in the membrane of pores, the development of which is promoted by an electric field. 相似文献
8.
The uptake and efflux of 22Na and 42K were studied in denuded Rana pipiens oocytes following progesterone induction of the resumption of meiotic maturation. Coincident with the breakdown of the large nucleus, or germinal vesicle, there is a virtual disappearance of K+ permeability of the oocyte plasma membrane. Only about 1–2% of the total [K+]i is exchanged by completion of nuclear breakdown (8–10 hr) and accounts for the finding that there is no detectable change in total [K+]i during the first meiotic division (20–24 hr). In the case of Na+, influx, exchange, and efflux kinetics were unchanged during the first meiotic division, with 20 and 35% of the total oocyte Na+ exchanging by the completion of nuclear breakdown and first meiotic division, respectively. Removal of Na+ from the incubation medium produced and earlier nuclear breakdown, whereas a K-free medium delayed breakdown. There was no effect of 10 μm/ml tetrodotoxin or 10?5M strophanthidin on the time course of nuclear breakdown. Thus one action of progesterone appears to be a selective turning off of “K channels” in the oocyte plasma membrane. The disappearance of K selectivity of the oocyte plasma membrane coincides with plasma membrane depolarization, as well as nuclear swelling and breakdown. 相似文献
9.
The kinetics of the glucose oxidase-catalyzed reaction of glucose with O2, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O2 depletion or production. The O2 concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 ± 0.7) ×104 M−1s−1 at 37°C. For catalase-catalyzed H2O2 breakdown, the reaction order in [H2O2] was somewhat greater than unity at 37°C and well above unity at 25°C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O2], and subsequent addition of catalase caused [O2] to rise and then decrease to zero. The best fit of [O2] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s−1 and 0.090 s−1 respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O2 consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain. 相似文献
10.
A. N. Vasil’eva K. S. Klopovskii A. S. Kovalev D. V. Lopaev Yu. A. Mankelevich N. A. Popov A. T. Rakhimov T. V. Rakhimova 《Plasma Physics Reports》2005,31(4):325-337
The production of O2(a1Δg) singlet oxygen in non-self-sustained discharges in pure oxygen and mixtures of oxygen with noble gases (Ar or He) was studied experimentally. It is shown that the energy efficiency of O2(a1Δg production can be optimized with respect to the reduced electric field E/N. It is shown that the optimal E/N values correspond to electron temperatures of 1.2–1.4 eV. At these E/N values, a decrease in the oxygen percentage in the mixture leads to an increase in the excitation rate of singlet oxygen because of the increase in the specific energy deposition per O2 molecule. The onset of discharge instabilities not only greatly reduces the energy efficiency of singlet oxygen production but also makes it impossible to achieve high energy deposition in a non-self-sustained discharge. A model of a non-self-sustained discharge in pure oxygen is developed. It is shown that good agreement between the experimental and computed results for a discharge in oxygen over a wide range of reduced electric fields can be achieved only by taking into account the ion component of the discharge current. The cross section for the electron-impact excitation of O2(a1Δg and the kinetic scheme of the discharge processes with the participation of singlet oxygen are verified by comparing the experimental and computed data on the energy efficiency of the production of O2(a1Δg and the dynamics of its concentration. It is shown that, in the dynamics of O2(a1Δg molecules in the discharge afterglow, an important role is played by their deexcitation in a three-body reaction with the participation of O(3P) atoms. At high energy depositions in a non-self-sustained discharge, this reaction can reduce the maximal attainable concentration of singlet oxygen. The effect of a hydrogen additive to an Ar: O2 mixture is analyzed based on the results obtained using the model developed. It is shown that, for actual electron beam current densities, a significant energy deposition in a non-self-sustained discharge in the mixtures under study can be achieved due to the high rate of electron detachment from negative ions. In this case, however, significant heating of the mixture can lead to a rapid quenching of O2(a1Δg molecules by atomic hydrogen. 相似文献
11.
Inner voltage clamping. A method for studying interactions among hydrophobic ions in a lipid bilayer
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Ketterer, et al. (1971) have suggested that a combination of electrostatic and chemical interactions may cause hydrophobic ions absorbed within a bilayer lipid membrane to reside in two potential wells, each close to a membrane surface. The resulting two planes of charges would define three regions of membrane dielectric: two identical outer regions each between a plane of absorbed charges and the plane of closest approach of ions in the aqueous phase; and the inner region between the two planes of adsorbed charges. The theory describing charge translocation across the inner region is based on a simple three-capacitor model. A significant theoretical conclusion is that the difference between the voltage across the inner region, Vi, and the voltage across the entire membrane, Vm, is directly proportional to the amount of charge that has flowed in a voltage clamp experiment. We demonstrate that we can construct an “inner voltage clamp” that can maintain, with positive feedback, a constant inner voltage, Vi. The manifestation of proper feedback is that the clamp current (after a voltage step) will exhibit pure (i.e., single time-constant) exponential decay, because the voltage dependent rate constants governing translocation will be independent of time. The “pureness” of the exponential is maximized when the standard deviation of the least-square fit of the appropriate exponential equation to the experimental data is minimized. The concomitant feedback is directly related to the capacitances of the inner and outer membrane regions, Ci and Co.
Experimental results with tetraphenylborate ion adsorbed in bacterial phosphatidylethanolamine/n-decane bilayers indicate Ci ~ 5 · 10-7F/cm2 and Co ≈ 5 · 10-5F/cm2.
相似文献12.
N. U. Barinov S. A. Budkov G. I. Dolgachev D. D. Maslennikov I. A. Khodeev 《Plasma Physics Reports》2002,28(3):177-182
The influence of an external magnetic field on the performance of a high-impedance plasma opening switch is studied experimentally. A 1.5-fold increase in the output voltage of a plasma opening switch operating in the erosion mode is achieved by applying an external magnetic field. The magnetic field strength and the parameters of the plasma opening switch at which the maximum output voltage is attained are determined. It is shown experimentally that the predicted dependence of the maximum output voltage on the Marx generator voltage, U POS [MV]=3.6 (U MG [MV])4/7, is confirmed experimentally. 相似文献
13.
J Murari 《Archives of biochemistry and biophysics》1977,181(1):1-4
Oxygen equilibrium determinations with “unsymmetrical” MetHb/Hb hybrids derived from human hemoglobins A and S are reported. All four of the possible hybrids have higher oxygen affinity than the parent hemoglobins. The α2Metβ2S hybrid has a lower oxygen affinity than that of α2Metβ2S. However, both the βMet hybrids have similar oxygen affinity. The Bohr value of α2Metβ2S is more negative than that of α2Metβ2A while the βMet hybrids appear to have almost identical Bohr values. These findings favor the view that α and β chains in hemoglobin A have different conformations and indicate that hemoglobin S has a β-chain conformation different from that of β-chain of hemoglobin A. This difference is probably carried into the oxygenation properties of the α-chain in such a way as to be reflected only when the β chain is oxidized. 相似文献
14.
I. V. Schweigert A. L. Alexandrov P. A. Bokhan Dm. E. Zakrevskiy 《Plasma Physics Reports》2016,42(7):666-677
Investigations of high-voltage open discharge in helium have shown a possibility of generation of current pulses with subnanosecond front rise, due to ultra-fast breakdown development. The open discharge is ignited between two planar cathodes with mesh anode in the middle between them. For gas pressure 6 Torr and 20 kV applied voltage, the rate of current rise reaches 500 A/(cm2 ns) for current density 200 A/cm2 and more. The time of breakdown development was measured for different helium pressures and a kinetic model of breakdown in open discharge is presented, based on elementary reactions for electrons, ions and fast atoms. The model also includes various cathode emission processes due to cathode bombardment by ions, fast atoms, electrons and photons of resonant radiation with Doppler shift of frequency. It is shown, that the dominating emission processes depend on the evolution of the discharge voltage during the breakdown. In the simulations, two cases of voltage behavior were considered: (i) the voltage is kept constant during the breakdown; (ii) the voltage is reduced with the growth of current. For the first case, the exponentially growing current is maintained due to photoemission by the resonant photons with Doppler-shifted frequency. For the second case, the dominating factor of current growth is the secondary electron emission. In both cases, the subnanosecond rise of discharge current was obtained. Also the effect of gas pressure on breakdown development was considered. It was found that for 20 Torr gas pressure the time of current rise decreases to 0.1 ns, which is in agreement with experimental data. 相似文献
15.
The rod cells in frog taste discs display the outward current and maintain the negative resting potential in the condition where internal K+ is replaced with Cs+. We analyzed the properties of the Cs+-permeable conductance in the rod cells. The current–voltage (I/V) relationships obtained by a voltage ramp were bell-shaped under Cs+ internal solution. The steady state I/V relationships elicited by voltage steps also displayed the bell-shaped outward current. The activation of the current accelerated with the depolarization and the inactivation appeared at positive voltage. The gating for the current was maintained even at symmetric condition (Cs+ external and internal solutions). The wing cells did not show the properties. The permeability for K+ was a little larger than that for Cs+. Internal Na+ and NMDG+ could not induce the bell-shaped outward current. Carbenoxolone inhibited the bell-shaped outward Cs+ current dose dependently (IC50: 27 μM). Internal arachidonic acid (20 μM) did not induce the linear current–voltage (I–V) relationship which is observed in two-pore domain K+ channel (K2P). The results suggest that the resting membrane potentials in the rod cells are maintained by the voltage-gated K+ channels. 相似文献
16.
Martina Klejchova Fernanda A L Silva-Alvim Michael R Blatt Jonas Chaves Alvim 《Plant physiology》2021,185(4):1523
Membrane voltage arises from the transport of ions through ion-translocating ATPases, ion-coupled transport of solutes, and ion channels, and is an integral part of the bioenergetic “currency” of the membrane. The dynamics of membrane voltage—so-called action, systemic, and variation potentials—have also led to a recognition of their contributions to signal transduction, both within cells and across tissues. Here, we review the origins of our understanding of membrane voltage and its place as a central element in regulating transport and signal transmission. We stress the importance of understanding voltage as a common intermediate that acts both as a driving force for transport—an electrical “substrate”—and as a product of charge flux across the membrane, thereby interconnecting all charge-carrying transport across the membrane. The voltage interconnection is vital to signaling via second messengers that rely on ion flux, including cytosolic free Ca2+, H+, and the synthesis of reactive oxygen species generated by integral membrane, respiratory burst oxidases. These characteristics inform on the ways in which long-distance voltage signals and voltage oscillations give rise to unique gene expression patterns and influence physiological, developmental, and adaptive responses such as systemic acquired resistance to pathogens and to insect herbivory.Membrane voltage serves as a platform coordinating ion flux to transmit and transduce biological signals. Advances
- The biophysics of transport that determine membrane voltage are well-described with quantitative flux equations.
- In the models of the guard cell and the giant algae Chara and Nitella these charge-transporting processes accurately describe and predict physiological behavior, including the coupling of membrane voltage oscillations with ion flux, [Ca2+]i, pH, their consequences for cellular osmotic adjustments, and their spatial propagation.
- Unlike neuronal and other animal tissues, action potentials in plants are mediated by a temporal sequence of ion flux through Ca2+ and Cl- channels with voltage recovery driven by ion flux through K+ channels. The interplay of channel-mediated ion flux and changes in H+-ATPase activity are likely responsible for the slower propagation of variation and systemic potentials.
- In terrestrial plants, membrane voltage transients may propagate along vascular traces, both through the parenchymal cells lining the xylem and through the phloem. Propagation of such voltage transients is associated with glutamate receptor-like channels that may contribute to plasma membrane Ca2+ flux and [Ca2+]i elevations.
- Changes in [Ca2+]i, pH, and reactive oxygen species are key mediators that translate voltage signals into physiological, developmental, and adaptive responses in plant tissues.
17.
K. K. Trusov 《Plasma Physics Reports》2014,40(9):739-753
Experimental results and model concepts concerning the relation between the index K of the interelectrode gap filling with spark channels and the peak current I peak of a single-pulse submicrosecond multichannel complete sliding discharge on an alumina ceramic surface are discussed. The spatial structure of an incomplete discharge at the threshold for the surface spark breakdown of gas is considered. The experiments were performed with three gases, Ne, Ar, and Xe, at pressures of 30 and 100 kPa and opposite polarities of the discharge voltage, with two discharge chambers differing in the geometry of the discharge gap and the thickness of the ceramic plate. It is shown that, although the structure of the incomplete discharge at the threshold for spark breakdown varies from diffuse homogeneous to pronounced filamentary, the dependence \(K\left( {\sqrt[6]{{I_{peak} }}} \right)\) for a complete discharge is close to linear and can be qualitatively explained by the earlier proposed semiempirical model of the time evolution of the structure of a multichannel discharge. In particular, the estimated steepness of the dependence \(K\left( {\sqrt[6]{{I_{peak} }}} \right)\) agrees best with the experimental results when the local density of free electrons at the threshold for spark breakdown is 1016 cm?3 or higher. 相似文献
18.
The kinetic and steady-state properties of macroscopic mslo Ca-activated K+ currents were studied in excised patches from Xenopus oocytes. In response to voltage steps, the timecourse of both activation and deactivation, but for a brief delay in activation, could be approximated by a single exponential function over a wide range of voltages and internal Ca2+ concentrations ([Ca]i). Activation rates increased with voltage and with [Ca]i, and approached saturation at high [Ca]i. Deactivation rates generally decreased with [Ca]i and voltage, and approached saturation at high [Ca]i. Plots of the macroscopic conductance as a function of voltage (G-V) and the time constant of activation and deactivation shifted leftward along the voltage axis with increasing [Ca]i. G-V relations could be approximated by a Boltzmann function with an equivalent gating charge which ranged between 1.1 and 1.8 e as [Ca]i varied between 0.84 and 1,000 μM. Hill analysis indicates that at least three Ca2+ binding sites can contribute to channel activation. Three lines of evidence indicate that there is at least one voltage-dependent unimolecular conformational change associated with mslo gating that is separate from Ca2+ binding. (a) The position of the mslo G-V relation does not vary logarithmically with [Ca]i. (b) The macroscopic rate constant of activation approaches saturation at high [Ca]i but remains voltage dependent. (c) With strong depolarizations mslo currents can be nearly maximally activated without binding Ca2+. These results can be understood in terms of a channel which must undergo a central voltage-dependent rate limiting conformational change in order to move from closed to open, with rapid Ca2+ binding to both open and closed states modulating this central step. 相似文献
19.
《Process Biochemistry》2010,45(4):467-474
The overall objective of this work was to investigate the modifications that occur in Bacillus subtilis lipid membrane during induced oxidative stress caused by reactive oxygen species (ROS), via an electrophysiological approach. Further, based on the results, we have developed and demonstrated a novel strategy to enhance specific enzyme production. Electrical parameters such as phase angle (θ), impedance (Z), capacitance (C) and breakdown voltage of reconstituted bilayer lipid membrane (BLM) composed of lipids extracted from non-stressed, mildly stressed (2.5 mM H2O2) and strongly stressed (2.5 mM H2O2 with 100 μM FeSO4) B. subtilis were compared. Strongly stressed BLM showed lower values of θ (10°), Z (0.4 Mohm), and breakdown voltage (100 mV) in comparison with those observed for non-stressed BLM, i.e., 30°, 0.5 Mohm and 250 mV, respectively. The capacitance of strongly stressed BLM, however, was higher (2.28 nF) compared to that of the non-stressed BLM (0.4 nF). These results suggest that under strongly stressed conditions, the lipids were loosely packed that resulted in a more permeable BLM. The higher permeability seems to result, unexpectedly, from a higher unsaturated fatty acid (UFA) synthesis and membrane incorporation (UFA fraction increased by 227%), and expectedly, from increased lipid peroxidation (increased by nearly 200%) in the BLM. A strategy that is based on increased membrane permeability due to induced ROS, enhanced specific amylase and protease production under oxidative stress by 62% and 137%, respectively. 相似文献
20.
Potassium Channels in Myelinated Nerve : Selective permeability to small cations 总被引:46,自引:23,他引:23
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Bertil Hille 《The Journal of general physiology》1973,61(6):669-686
The permeability of K channels to various cations is studied in myelinated nerve. Ionic currents under voltage clamp are measured in Ringer solution containing tetrodotoxin and a high concentration of the test ion. Reversal potentials for current in K channels are determined and used with the Goldman-Hodgkin-Katz equation to calculate relative permeabilities. The ratios PTl:PK:PRb:PNHNH4 are 2.3:1.00:0.92:0.13. No other ions are found to be measurably permeant including Li+, Na+, Cs+, methylamine, guanidine, hydrazine, or hydroxylamine. The ratio PNa/PK is less than 0.01. Potassium conductance is depressed at pH values below 5.0. Leakage conductance is higher in K, Rb, Cs, NH4, and Tl Ringer than in Na Ringer, but the selectivity sequence probably is not the same as for K channels. The hypothesis is offered that the narrowest part of the K channel is a circle of oxygen atoms about 3 Å in diameter with low electrostatic field strength. 相似文献