The Action Potential in Chara corallina IV.* Activation Enthalpies of the Hodgkin-Huxley Gates

1979 ◽  
Vol 6 (3) ◽  
pp. 355
Author(s):  
M.J Beilby ◽  
H.G.L Coster
Keyword(s):  
Membrane Potential ◽  
Resting State ◽  
Activation Enthalpy ◽  
Chara Corallina ◽  
Effect Of Temperature ◽  
Ca Channels ◽  
Precursor State ◽  
Time Constants ◽  
Increasing Temperature ◽  
Current Transients

Voltage-clamp experiments were made to determine the effect of temperature on the Hodgkin-Huxley parameters describing the excitation of the plasmalemma of C. covallina. In these cells two activated and inactivated transients in addition to a potential-dependent leak conductance occur during excitation. The activation and inactivation time constants for both the Cl- and X (� Ca�+?) channels decreased with increasing temperature. The relative changes with temperature, however, were the same at all potentials. That is, the thermodynamic activation enthalpies for activation and inactivation were independent of membrane potential. This suggests that these parts of the gating processes do not involve movement, normal to the membrane, of charged moieties (other than the ions carrying the clamp currents). For clamps beyond the threshold, both gated current transients occur only after a delay, the latter being strongly dependent on the clamp potential. The delays �*Cl and �*x in the Cl- transient and X (� Ca�+?) transients, respectively, both decreased with increasing temperature, having values �*Cl � 0.8 s and �*x � 2.5 s at - 110 mV and 20�C. Apparently activation/inactivation commenced only after the resting-state channels had been transformed into some precursor state for excitation. The activation enthalpy for this transformation varied linearly with membrane clamp potential at a rate of ~ - 390 kJ per mol per volt and ~ -960 kJ per mol per volt for the CI- and X (� Ca�+?) channels respectively. The transformation to the precursor state therefore required the same energy as the separation (positive charges outwards, negative charges inwards), normal to the plasmalemma, of ~4 and ~10 charges per molecule for the Cl- and X channels, respectively.

The Action Potential in Chara corallina: Effect of Temperature

1976 ◽  
Vol 3 (3) ◽  
pp. 275 ◽  
Author(s):  
MJ Beilby ◽  
HGJ Coster
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Chara Corallina ◽  
Transient Current ◽  
Effect Of Temperature ◽  
Progressive Change ◽  
Low Frequencies ◽  
Voltage Clamps ◽  
Conductance Changes ◽  
Increasing Temperature

An investigation has been made of the effect of temperature on excitation in cells of C. corallina. It was found that the duration both of the action potential and of the transient current during excitation under voltage clamp increased with decreasing temperature, from ~1 s at 40°C to ~30 s at 3.5°C. The form of the transient response, however, was independent of temperature. While the peak potential during an action potential was largely independent of temperature, the peak transient current during a voltage clamp increased with increasing temperature up to ~30°C. Beyond this temperature, the peak current decreased again with increasing temperature. The activation enthalphy (ΔH*) calculated from Arrhenius plots of the duration of the action potential or of the transient current under voltage clamp varied continuously with temperature, having the values of ~7 kJ/mol for T > 20°C and ~350 kJ/mol for T < 7°C. The peak of the transient conductance changes (during voltage clamp at -45 mV) increased progressively with increasing temperatures; for T < 7°C there was almost no transient change in conductance. °H* for peak transient conductance change was ~7 kJ/mol for T > 20°C and ~145 kJ/mol for T < 7°C. At low temperatures (<7°C), ΔH* for the excitation channels was similar to that for the dehydration of K+, Na+ or Cl- ions. At high temperatures (>35°C), ΔH* for both the passive and excitation channels was about the same as that for diffusion in a free solution. This suggests a progressive change in the degree of dehydration required for ion permeation in the channels. In the light of the known frequency dependence of the membrane capacitance of this species (at low frequencies), considerations are also given to the implications of the similarity in their temperature dependence, of the duration of the action potential and the duration of the transient currents during voltage clamps.

scholarly journals Theoretical Effect of Temperature on Threshold in the Hodgkin-Huxley Nerve Model

1966 ◽  
Vol 49 (5) ◽  
pp. 989-1005 ◽  
Author(s):  
Richard Fitzhugh
Keyword(s):  
Relaxation Time ◽  
Relaxation Times ◽  
Giant Axon ◽  
Temperature Curve ◽  
Effect Of Temperature ◽  
Threshold Temperature ◽  
Ionic Conductances ◽  
And Shifts ◽  
The Right ◽  
Increasing Temperature

In the squid giant axon, Sjodin and Mullins (1958), using 1 msec duration pulses, found a decrease of threshold with increasing temperature, while Guttman (1962), using 100 msec pulses, found an increase. Both results are qualitatively predicted by the Hodgkin-Huxley model. The threshold vs. temperature curve varies so much with the assumptions made regarding the temperature-dependence of the membrane ionic conductances that quantitative comparison between theory and experiment is not yet possible. For very short pulses, increasing temperature has two effects. (1) At lower temperatures the decrease of relaxation time of Na activation (m) relative to the electrical (RC) relaxation time favors excitation and decreases threshold. (2) For higher temperatures, effect (1) saturates, but the decreasing relaxation times of Na inactivation (h) and K activation (n) factor accommodation and increased threshold. The result is a U-shaped threshold temperature curve. R. Guttman has obtained such U-shaped curves for 50 µsec pulses. Assuming higher ionic conductances decreases the electrical relaxation time and shifts the curve to the right along the temperature axis. Making the conductances increase with temperature flattens the curve. Using very long pulses favors effect (2) over (1) and makes threshold increase monotonically with temperature.

Influence of anomalous rectifier activation on afterhyperpolarizations of neurons from cat sensorimotor cortex in vitro

1988 ◽  
Vol 59 (2) ◽  
pp. 468-481 ◽  
Author(s):  
P. C. Schwindt ◽  
W. J. Spain ◽  
W. E. Crill
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Sensorimotor Cortex ◽  
Model Parameters ◽  
Fast Decay ◽  
Time Constants ◽  
Anomalous Rectifier ◽  
Betz Cells ◽  
K Currents

1. Large neurons from layer V of cat sensorimotor cortex (Betz cells) were studied to determine the influence of the anomalous rectifier current (IAR) on slow afterhyperpolarizations (AHPs). The neurons were examined using intracellular recording and single-microelectrode voltage clamp in an in vitro brain slice preparation. 2. A faster medium-duration AHP (mAHP) and slower AHP (sAHP) followed repetitive firing (22, 23). The amplitude of the mAHP often increased or remained constant during membrane potential hyperpolarization. The membrane potential trajectory resulting solely from IAR activation was similar to the mAHP. 3. Postrepetitive firing voltage clamp was used to measure directly slowly decaying K+ currents (IK) and IAR at different membrane potentials. IK exhibited both a fast and slow decay. The time constants of the fast decay of IK and IAR activation were similar. IAR increased with hyperpolarization or raised extracellular K+ concentration [( K+]o), whereas both the fast and slow components of IK reversed or nulled near -100 mV and behaved as pure K+ currents in response to raised [K+]o. 4. To determine the precise contribution of IK and IAR to the AHP waveform, theoretical AHPs were computed using a quantitative model based on voltage-clamp measurements. The calculated AHPs were qualitatively similar to measured AHPs. The amplitude of the mAHP showed little change with hyperpolarization because of the increasing dominance of IAR at more negative membrane potentials. The sAHP was little affected by IAR activation. 5. Several model parameters subject to biological variation among Betz cells were varied in the calculations to determine their importance in the AHP waveform. With IK parameters held constant, the amplitude and time course of the mAHP depended on resting potential, membrane time constant, the kinetics of the anomalous rectifier conductance (GAR), and the maximum value of GAR. IAR activation could result in a biphasic AHP even when the fast decay of IK was omitted from the calculations. 6. A wider variation of model parameters revealed behavior that may be relevant to other neurons. Certain values of membrane or IAR activation time constants resulted in a monophasic AHP even when the fast decay of IK was present. The decay of a biphasic AHP could reflect either the onset of IAR or the fast decay of IK, depending on the relative value of their time constants. Procedures are outlined to discriminate between these possibilities using current clamp methods.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals DFT calculation for the electronic properties and quantum capacitance of pure and doped Zr2CO2 as electrode of supercapacitors

2021 ◽  
Author(s):  
Shuo Xu ◽  
Shi-Jie Wang ◽  
Li Xiao-Hong ◽  
Hong-Ling Cui
Keyword(s):  
Electronic Properties ◽  
Electrode Materials ◽  
Chemical Properties ◽  
Effect Of Temperature ◽  
Quantum Capacitance ◽  
Substitutional Site ◽  
Level Shifts ◽  
Dirac Distribution ◽  
Increasing Temperature ◽  
Physical And Chemical

Defect and doping are effective methods to modulate the physical and chemical properties of materials. In this report, we investigated the structural stability, electronic properties and quantum capacitance (Cdiff) of Zr2CO2 by changing the dopants of Si, Ge, Sn, N, B, S and F in the substitutional site. The doping of F, N, and S atoms makes the system undergo the semiconductor-to-conductor transition, while the doping of Si, Ge, and Sn maintains the semiconductor characteristics. The Cdiff of the doped systems are further explored. The B-doped system can be used as cathode materials, while the systems doped by S, F, N, Sn atoms are promising anode materials of asymmetric supercapacitors, especially for the S-doped system. The improved Cdiff mainly originates from Fermi-level shifts and Fermi-Dirac distribution by the introduction of the dopant. The effect of temperature on Cdiff is further explored. The result indicates that the maximum Cdiff of the studied systems gradually decreases with the increasing temperature. Our investigation can provide useful theoretical basis for designing and developing the ideal electrode materials for supercapacitors.

scholarly journals Effects of the Temperature and the pH on the Main Protease of SARS-CoV-2: A Molecular Dynamics Simulation Study

2021 ◽  
Vol 12 (6) ◽  
pp. 7239-7248
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Root Mean Square ◽  
Dynamics Simulation ◽  
Effect Of Temperature ◽  
Water Molecules ◽  
Mean Square ◽  
Main Protease ◽  
Decreasing Ph ◽  
Increasing Temperature

The novel coronavirus, recognized as COVID-19, is the cause of an infection outbreak in December 2019. The effect of temperature and pH changes on the main protease of SARS-CoV-2 were investigated using all-atom molecular dynamics simulation. The obtained results from the root mean square deviation (RMSD) and root mean square fluctuations (RMSF) analyses showed that at a constant temperature of 25℃ and pH=5, the conformational change of the main protease is more significant than that of pH=6 and 7. Also, by increasing temperature from 25℃ to 55℃ at constant pH=7, a remarkable change in protein structure was observed. The radial probability of water molecules around the main protease was decreased by increasing temperature and decreasing pH. The weakening of the binding energy between the main protease and water molecules due to the increasing temperature and decreasing pH has reduced the number of hydrogen bonds between the main protease and water molecules. Finding conditions that alter the conformation of the main protease could be fundamental because this change could affect the virus’s functionality and its ability to impose illness.

scholarly journals Partial purification and properties of the two common inherited forms of human erythrocyte adenylate kinase

1972 ◽  
Vol 130 (3) ◽  
pp. 797-803 ◽  
Author(s):  
C. Brownson ◽  
N. Spencer
Keyword(s):  
Adenylate Kinase ◽  
Effect Of Temperature ◽  
Partial Purification ◽  
Heat Denaturation ◽  
Gel Chromatography ◽  
Molecular Weights ◽  
Purification And Properties ◽  
Increasing Temperature

1. The partial purification of adenylate kinase, types 1 and 2, from human erythrocytes is described. 2. Gel chromatography of both forms of the enzyme gave estimates of the molecular weights in the range 20000–23000. 3. Studies on crude haemolysates at various pH values indicated that the type 2 enzyme was less stable than the type 1. Heat denaturation studies on the partially purified enzymes confirmed these findings. 4. Measurements of rates of inhibition by iodoacetate and iodoacetamide showed that the type 2 enzyme reacts more readily than the type 1 enzyme with both reagents. 5. The effect of temperature on the initial velocity of ADP formation was measured at a single concentration of both AMP and MgATP2-. The two forms of the enzyme responded differently to increasing temperature.

Standardized reaction times used to describe the mechanism of enzyme-induced gelation in whey protein systems

2000 ◽  
Vol 67 (3) ◽  
pp. 403-413 ◽  
Author(s):  
RICHARD IPSEN ◽  
JEANETTE OTTE ◽  
STIG B. LOMHOLT ◽  
KARSTEN B. QVIST
Keyword(s):  
Whey Protein ◽  
Reaction Times ◽  
Enzyme Concentration ◽  
Protein Isolate ◽  
Effect Of Temperature ◽  
Degree Of Hydrolysis ◽  
Thermally Induced ◽  
Constant Degree ◽  
Increasing Temperature ◽  
Rate Limiting

Whey protein isolate (WPI), either untreated or pretreated at 80 °C for 30 min, was incubated with a proteinase from Bacillus licheniformis until a gel was formed. Standardized reaction times, directly linked to the degree of hydrolysis, were obtained from plots of the relative amount of peptides released v. reaction time obtained under different conditions (enzyme concentration, temperature, pH, NaCl addition). This provided a connection between the gelation profile and the degree of hydrolysis. In the case of untreated WPI, gelation occurred at lower degrees of proteolysis when the enzyme concentration was decreased, demonstrating that a rate-limiting aggregation process occurred at the same time as the proteolysis in a manner similar to the renneting of milk. This was not the case for preheated WPI, when gelation was found to take place at a constant degree of proteolysis, independent of the enzyme concentration. In this case, the mechanism could be described by assuming the thermally induced aggregates present in this substrate had progressively more stabilizing peptide segments shaved off, resulting in increased attraction between individual aggregates that ultimately led to gelation. Results obtained at 40–60 °C supported this, as we found no effect of temperature on the degree of proteolysis at gelation for the untreated WPI, whereas the degree of proteolysis decreased with increasing temperature when heated WPI was hydrolysed. The effect of pH and NaCl addition on the process was to reduce repulsion between the aggregating species so that gelation was induced at a decreased degree of proteolysis.

Cl - channels in Chara

1982 ◽  
Vol 299 (1097) ◽  
pp. 435-445 ◽  
Keyword(s):  
Mathematical Model ◽  
Action Potential ◽  
Voltage Dependence ◽  
Quantitative Description ◽  
Chara Corallina ◽  
Squid Axon ◽  
Impedance Measurements ◽  
Time Constants ◽  
Effects Of Ph ◽  
Cl Channels

The action potential in the cells of the freshwater alga Chara corallina is slower than that in the nerve by about 1000-fold. The depolarization phase is brought on by the outflow of the Cl - ions. Voltage-clamp studies show that this Cl - current can be described by the Hodgkin-Huxley equations for the Na+ transient in the squid axon. The only change necessary to the form of the Hodgkin-Huxley equations is an introduction of a time delay between the stimulus and the onset of excitation. This mathematical model of the Chara action potential facilitates a quantitative description of the effects of pH and temperature. While a pH shift alters various Hodgkin-Huxley parameters, temperature change influences mainly the activation and inactivation time constants but leaves the voltage-dependence of these parameters unaffected. The delays in excitation are both temperature and potential dependent. In future some corrections to the Hodgkin-Huxley picture of the Chara action potential may be necessary, as recent impedance measurements suggest a change in the membrane capacitance at the time of excitation.

Modeling and Numerical Simulation of the Effect of Temperature on the LCF Behaviour of a CuCrZr Alloy Specimen

2020 ◽  
Vol 50 ◽  
pp. 37-47
Author(s):  
M. Benhaddou ◽  
M. Ghammouri ◽  
Z. Hammouch ◽  
F. Latrache
Keyword(s):  
Test Piece ◽  
Low Cycle Fatigue ◽  
Effect Of Temperature ◽  
Cycle Fatigue ◽  
Alloy Specimen ◽  
Number Of Cycles ◽  
Increasing Temperature ◽  
Relationship Of ◽  
The Relationship ◽  
Cylindrical Test

The main originality of this work consists in investigating low cycle fatigue of cylindrical test piece with wings under imposed constraint and for the temperature 20°c, 200°c, 400°c. Based on a combination between the fatigue parameter of Jiang-Sehitoglu and the relationship of Coffin-Manson, a numerical model for the prediction of the number of cycles at break. It was found that the CuCrZr cylindrical test piece showed a reduction in fatigue life with increasing temperature.

scholarly journals Modulation of Astrocytes on Mode Selection of Neuron Firing Driven by Electromagnetic Induction

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Zhongquan Gao ◽  
Zhixuan Yuan ◽  
Zuo Wang ◽  
Peihua Feng
Keyword(s):  
Membrane Potential ◽  
Resting State ◽  
Electromagnetic Induction ◽  
Neuron Model ◽  
Mode Selection ◽  
Neuron Firing ◽  
Two Factors ◽  
Selection Of ◽  
Strong Ability

Both of astrocytes and electromagnetic induction are magnificent to modulate neuron firing by introducing feedback currents to membrane potential. An improved astro-neuron model considering both of the two factors is employed to investigate their different roles in modulation. The mixing mode, defined by combination of period bursting and depolarization blockage, characterizes the effect of astrocytes. Mixing mode and period bursting alternatively appear in parameter space with respect to the amplitude of feedback current on neuron from astrocyte modulation. However, magnetic flux obviously plays a role of neuron firing inhibition. It not only repels the mixing mode but also suppresses period bursting. The mixing mode becomes period bursting mode and even resting state when astrocytes are hyperexcitable. Abnormal activities of astrocytes are capable to induce depolarization blockage to compose the mixing mode together with bursting mode. But electromagnetic induction shows its strong ability of inhibition of neuron firing, which is also illustrated in the bifurcation diagram. Indeed, the combination of the two factors and appropriate choice of parameters show the great potential to control disorder of neuron firing like epilepsy.

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