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 Ionic Relations of Cells of Chara Australis VIII. Membrane Currents During a Voltage Clamp

1964 ◽  
Vol 17 (2) ◽  
pp. 388 ◽  
Author(s):  
GP Findlay
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Detailed Analysis ◽  
Voltage Clamp ◽  
Membrane Currents ◽  
Voltage Clamps ◽  
Transient Activity ◽  
Predetermined Level ◽  
Chara Australis ◽  
Ionic Relations

Experiments are described in which "voltage clamps" were applied to the "membrane" of O. australis cells comprising tonoplast and plasmalemma and also to the plasmalemma alone. The voltage-clamp system maintained the membrane potential at a predetermined level, and enabled a detailed analysis to be made of the transient electrical phenomena occurring during the action potential. A scarming technique is also described, by means of which the membrane currentpotential characteristics could be determined at any particular time during the transient activity of the membrane.

scholarly journals Current- and Voltage-Clamped Studies on Myxicola Giant Axons

1969 ◽  
Vol 54 (6) ◽  
pp. 730-740 ◽  
Author(s):  
L. Binstock ◽  
L. Goldman
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Action Potential ◽  
Voltage Clamp ◽  
Transient Current ◽  
Resting Membrane Potential ◽  
Action Potential Amplitude ◽  
Giant Axons ◽  
Potential Amplitude ◽  
Steady State Current

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm2 and 1.22 KΩ cm 2 respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.

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.

Effect of Temperature, Velocity Gradient and I.V. Heparin on in Vitro Blood Coagulation and Platelet Aggregation

1967 ◽  
Vol 17 (01/02) ◽  
pp. 112-119 ◽  
Author(s):  
L Dintenfass ◽  
M. C Rozenberg
Keyword(s):  
Blood Coagulation ◽  
Velocity Gradient ◽  
Elevated Temperatures ◽  
Morphological Changes ◽  
Effect Of Temperature ◽  
Clotting Time ◽  
Progressive Change ◽  
Aggregation Of Platelets ◽  
Microscopic Techniques

SummaryA study of blood coagulation was carried out by observing changes in the blood viscosity of blood coagulating in the cone-in-cone viscometer. The clots were investigated by microscopic techniques.Immediately after blood is obtained by venepuncture, viscosity of blood remains constant for a certain “latent” period. The duration of this period depends not only on the intrinsic properties of the blood sample, but also on temperature and rate of shear used during blood storage. An increase of temperature decreases the clotting time ; also, an increase in the rate of shear decreases the clotting time.It is confirmed that morphological changes take place in blood coagula as a function of the velocity gradient at which such coagulation takes place. There is a progressive change from the red clot to white thrombus as the rates of shear increase. Aggregation of platelets increases as the rate of shear increases.This pattern is maintained with changes of temperature, although aggregation of platelets appears to be increased at elevated temperatures.Intravenously added heparin affects the clotting time and the aggregation of platelets in in vitro coagulation.

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.

scholarly journals The effect of temperature on spontaneous action potential discharge of the isolated sinus venosus from winter and summer plaice (Pleuronectes platessa)

1995 ◽  
Vol 198 (1) ◽  
pp. 137-140 ◽  
Author(s):  
A A Harper ◽  
I P Newton ◽  
P W Watt
Keyword(s):  
Action Potential ◽  
Discharge Rate ◽  
Cardiac Pacemaker ◽  
Intrinsic Rate ◽  
Effect Of Temperature ◽  
Pacemaker Activity ◽  
Duration Of Action ◽  
Diastolic Depolarization ◽  
Significant Difference

The spontaneous cardiac pacemaker activity and conformation were recorded in vitro, using intracellular recording methods, from heart tissue of summer- and winter-caught plaice. The effects of changing temperature on the pacemaker rate, duration of action potential and diastolic depolarization were investigated by altering the temperature of the superfusing medium. The resting intrinsic rate of discharge was significantly greater in pacemaker cells from winter plaice (P=0.05), but there was no significant difference between winter and summer fish in the apparent Arrhenius activation energies for this process. However, there was a significant difference in the estimated intercept, indicating a thermal shift in the processes underlying the spontaneous pacemaker rhythm. There was no significant difference in the diastolic depolarization duration recorded from winter and summer fish over the temperature range 4&shy;22 &deg;C. The major effect of previous environmental temperature was on the duration of the action potential (P&lt;0.02), indicating that the observed changes in pacemaker discharge rate were not influenced by the processes that determine the duration of the pacemaker diastolic depolarisation but were modulated by the channel events that give rise to the action potential.

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 Sinusoidal voltage protocols for rapid characterisation of ion channel kinetics

2017 ◽  
Author(s):  
Kylie A. Beattie ◽  
Adam P. Hill ◽  
Rémi Bardenet ◽  
Yi Cui ◽  
Jamie I. Vandenberg ◽  
...  
Keyword(s):  
Ion Channel ◽  
Voltage Clamp ◽  
Ion Current ◽  
Ion Currents ◽  
Channel Kinetics ◽  
Sinusoidal Voltage ◽  
Square Wave ◽  
Voltage Clamps ◽  
Ion Channel Kinetics ◽  
Cell Cell

AbstractUnderstanding the roles of ion currents is crucial to predict the action of pharmaceuticals and mutations in different scenarios, and thereby to guide clinical interventions in the heart, brain and other electrophysiological systems. Our ability to predict how ion currents contribute to cellular electrophysiology is in turn critically dependent on our characterisation of ion channel kinetics — the voltage-dependent rates of transition between open, closed and inactivated channel states. We present a new method for rapidly exploring and characterising ion channel kinetics, applying it to the hERG potassium channel as an example, with the aim of generating a quantitatively predictive representation of the ion current. We fit a mathematical model to currents evoked by a novel 8 second sinusoidal voltage clamp in CHO cells over-expressing hERG1a. The model is then used to predict over 5 minutes of recordings in the same cell in response to further protocols: a series of traditional square step voltage clamps, and also a novel voltage clamp comprised of a collection of physiologically-relevant action potentials. We demonstrate that we can make predictive cell-specific models that outperform the use of averaged data from a number of different cells, and thereby examine which changes in gating are responsible for cell-cell variability in current kinetics. Our technique allows rapid collection of consistent and high quality data, from single cells, and produces more predictive mathematical ion channel models than traditional approaches.Table of Contents CategoryTechniques for Physiology1Key PointsIon current kinetics are commonly represented by current-voltage relationships, time-constant voltage relationships, and subsequently mathematical models fitted to these. These experiments take substantial time which means they are rarely performed in the same cell.Rather than traditional square-wave voltage clamps, we fit a model to the current evoked by a novel sum-of-sinusoids voltage clamp that is only 8 seconds long.Short protocols that can be performed multiple times within a single cell will offer many new opportunities to measure how ion current kinetics are affected by changing conditions.The new model predicts the current under traditional square-wave protocols well, with better predictions of underlying currents than literature models. The current under a novel physiologically-relevant series of action potential clamps is predicted extremely well.The short sinusoidal protocols allow a model to be fully fitted to individual cells, allowing us to examine cell-cell variability in current kinetics for the first time.

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