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.

Ionic Relations of Cells of Chara Australis IX. Analysis of Transient Membrane Currents

1964 ◽  
Vol 17 (2) ◽  
pp. 400 ◽  
Author(s):  
GP Findlay ◽  
AB Hope
Keyword(s):  
Voltage Clamp ◽  
Divalent Cations ◽  
Chloride Ion ◽  
Membrane Currents ◽  
Transient Current ◽  
Ion Concentration ◽  
Chara Australis ◽  
Strontium Ions ◽  
Ionic Relations ◽  
High Chloride

The effect of divalent cations and of high chloride ion concentration on voltage-clamp currents in the plasmalemma of O. australis was investigated. Either calcium or strontium ions were necessary in the medium for a transient current to appear during a voltage clamp_ The transient current with strontium was about 20% of that with calcium present. Barium. cadmium, magnesium, manganous, or nickelous ions were unable to replace calcium in. this function.

cAMP-independent effects of 8-(4-parachlorophenylthio)-cyclic AMP on spike duration and membrane currents in pleural sensory neurons of Aplysia

1994 ◽  
Vol 72 (3) ◽  
pp. 1250-1259 ◽  
Author(s):  
S. Sugita ◽  
D. A. Baxter ◽  
J. H. Byrne
Keyword(s):  
Protein Kinase ◽  
Action Potential ◽  
Voltage Clamp ◽  
Sensory Neurons ◽  
Membrane Current ◽  
Membrane Currents ◽  
Cyclic Monophosphate ◽  
Subsequent Application ◽  
Independent Effects

1. The serotonergic modulation of pleural sensory neurons in Aplysia is mediated via two second messenger systems: the adenosine cyclic monophosphate/protein kinase A (cAMP/PKA) and diacylglycerol/protein kinase C systems. Often membrane permeable derivatives of cAMP, such as 8-(4-parachlorophenylthio)-cAMP (pcpt-cAMP), have been used to investigate the role of cAMP/PKA in modulating sensory neurons. In light of recent findings that pcpt-cAMP may have cAMP-independent actions, we have reexamined the effects of pcpt-cAMP on the action potential and membrane currents of the sensory neurons. 2. Although pcpt-cAMP (500 microM to 1 mM) and serotonin (5-HT; 10 microM) induced comparable measures of spike broadening (an average increase above baseline of 29 and 40%, respectively), the broadening produced by the two was qualitatively different. Serotonin-induced broadening developed slowly over 9-12 min, was most prominent during later phases of the spike repolarization, and reduced the spike afterhyperpolarization. In contrast, pcpt-cAMP-induced broadening developed rapidly, was rather uniform throughout the repolarization phase of the spike, delayed the peak of the action potential, and increased the afterhyperpolarization. 3. Preexposure of sensory neurons to 5-HT did not occlude further spike broaden by subsequent application of pcpt-cAMP. Indeed the effects of the two were additive. In addition, the effects of pcpt-cAMP were not mimicked by another analogue of cAMP, 8-bromo-cAMP. Interestingly, most of the effects of pcpt-cAMP on the action potential were mimicked by 8-(4-parachlorophenyl-thio)-guanosine cyclic monophosphate (pcpt-cGMP), but not by 8-bromo-cGMP. 4. During voltage-clamp pulses to 20 mV, pcpt-cAMP reduced the membrane current throughout the voltage-clamp pulse, which was qualitatively different from the modulation of the membrane current by 5-HT. In addition, the pcpt-cAMP-induced reduction in the membrane current at the beginning of the pulse was much greater than that induced by 5-HT. Moreover, preexposure of sensory neurons to 5-HT did not occlude further reduction in the membrane current by subsequent application of pcpt-cAMP. 5. These results suggest that pcpt-cAMP has some mechanisms of action that are not shared by 5-HT or cAMP but are shared by pcpt-cGMP. In addition, these findings provide further evidence that results obtained with this compound should be interpreted with caution.

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.

Excitable properties and voltage-sensitive ion conductances of horizontal cells isolated from catfish (Ictalurus punctatus) retina

1986 ◽  
Vol 56 (1) ◽  
pp. 32-49 ◽  
Author(s):  
R. Shingai ◽  
B. N. Christensen
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Action Potential ◽  
Voltage Clamp ◽  
Ictalurus Punctatus ◽  
Horizontal Cells ◽  
Resting Potential ◽  
Patch Type ◽  
Voltage Range ◽  
Plateau Potential

External horizontal cells were enzymatically dissociated from intact catfish (Ictalurus punctatus) retina and pipetted onto a small chamber attached to the stage of an inverted phase-contrast microscope. Individual horizontal cells were recognized by their large size and restricted dendritic arborization. Low-resistance (3-12 M omega) patch-type electrodes were used to record intracellular potentials and to pass current across the cell membrane under either current or voltage-clamp conditions. The average resting potential of isolated horizontal cells was -67 V + 6.9 mV (mean +/- SD, n = 40). At the resting potential, the cell membrane appears to be mainly permeable to K. A depolarizing current step evoked an action potential in the cell. The maximum rate of rise of the action potential (dV/dt) in normal physiological solution was 6.5 +/- 1.8 V/s (means +/- SD, n = 24) and was reduced to 1.2 +/- 0.39 V/s (means +/- SD, n = 9) in 1-10 micron tetrodotoxin (TTX) and 3.2 +/- 1.4 V/s (means +/- SD, n = 6) in Ca-free solution. The maximum dV/dt was reduced in 10 mM extracellular K concentration [K]o to about half of that seen in standard saline, and values in 30 or 80 mM [K]o were similar to that measured in TTX. Following an action potential, the membrane potential reached a plateau potential of + 17.4 +/- 8.1 mV (means +/- SD, n = 17) and remained depolarized for variable periods of time lasting from less than a second to a few minutes. When the plateau potential was long lasting, the cell repolarized slowly and upon reaching zero rapidly repolarized to the original resting potential. The duration of the plateau potential decreased or was absent in saline containing one of the following calcium channel antagonists: La, Cd, Co, or Ni. The voltage-clamp technique was used to identify the membrane currents responsible for the membrane potential changes seen under current clamp. Experiments were carried out using either a single or two individual electrodes. Fast and steady-state inward currents were recorded from isolated horizontal cells in the voltage range between -20 and +20 mV. These currents were a result of increased membrane conductance to both Na and Ca ions. The Na channels are inactivated at depolarized potentials and are TTX sensitive. Ca channels are partially inactivated at depolarized potentials. The Ca conductance is decreased by Cd, Co, Ni, and La. Ba can substitute for Ca in the channel.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

scholarly journals Passive properties and membrane currents of canine ventricular myocytes.

1987 ◽  
Vol 90 (5) ◽  
pp. 671-701 ◽  
Author(s):  
G N Tseng ◽  
R B Robinson ◽  
B F Hoffman
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Cardiac Cells ◽  
Membrane Currents ◽  
Membrane Properties ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Fast Kinetics

The membrane potential and membrane currents of single canine ventricular myocytes were studied using either single microelectrodes or suction pipettes. The myocytes displayed passive membrane properties and an action potential configuration similar to those described for multicellular dog ventricular tissue. As for other cardiac cells, in canine ventricular myocytes: (a) an inward rectifier current plays an important role in determining the resting membrane potential and repolarization rate; (b) a tetrodotoxin-sensitive Na current helps maintain the action potential plateau; and (c) the Ca current has fast kinetics and a large amplitude. Unexpected findings were the following: (a) in approximately half of the myocytes, there is a transient outward current composed of two components, one blocked by 4-aminopyridine and the other by Mn or caffeine; (b) there is clearly a time-dependent outward current (delayed rectifier current) that contributes to repolarization; and (c) the relationship of maximum upstroke velocity of phase 0 to membrane potential is more positive and steeper than that observed in cardiac tissues from Purkinje fibers.

A model of the action potential and underlying membrane currents in a rabbit atrial cell

1996 ◽  
Vol 271 (4) ◽  
pp. H1666-H1696 ◽  
Author(s):  
D. S. Lindblad ◽  
C. R. Murphey ◽  
J. W. Clark ◽  
W. R. Giles
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Membrane Currents ◽  
Whole Cell ◽  
Whole Cell Voltage Clamp ◽  
Voltage Dependent ◽  
Atrial Myocyte ◽  
Atrial Cell

We have developed a mathematical model of the rabbit atrial myocyte and have used it in an examination of the ionic basis of the atrial action potential. Available biophysical data have been incorporated into the model to quantify the specific ultrastructural morphology, intracellular ion buffering, and time- and voltage-dependent currents and transport mechanisms of the rabbit atrial cell. When possible, mathematical expressions describing ionic currents identified in rabbit atrium are based on whole cell voltage-clamp data from enzymatically isolated rabbit atrial myocytes. This membrane model is coupled to equations describing Na+, K+, and Ca2+ homeostasis, including the uptake and release of Ca2+ by the sarcoplasmic reticulum and Ca2+ buffering. The resulting formulation can accurately simulate the whole cell voltage-clamp data on which it is based and provides fits to a family of rabbit atrial cell action potentials obtained at 35 degrees C over a range of stimulus rates (0.2–3.0 Hz). The model is utilized to provide a qualitative prediction of the intracellular Ca2+ concentration transient during the action potential and to illustrate the interactions between membrane currents that underlie repolarization in the rabbit atrial myocyte.

A calcium-dependent transient outward current in Xenopus laevis oocytes

1982 ◽  
Vol 215 (1201) ◽  
pp. 491-497 ◽  
Keyword(s):  
Membrane Potential ◽  
Xenopus Laevis ◽  
Voltage Clamp ◽  
Outward Current ◽  
Membrane Currents ◽  
Transient Current ◽  
Transient Outward Current ◽  
Xenopus Laevis Oocytes ◽  
Calcium Dependent

Membrane currents were investigated in Xenopus laevis oocytes under voltage clamp. Depolarizing pulses, given from a holding potential of about –100 mV, elicited a transient outward current when the membrane potential was made more positive than about –20 mV. As the potential was made increasingly positive the transient outward current first increased and then decreased. The amplitude of the transient current increased when the external Ca 2+ concentration was raised; and the current was abolished by Mn 2+ . It appears that when the membrane is depolarized Ca 2+ ions enter the oocyte and trigger an outward current, possibly by opening Cl – channels.

Ionic pores, gates, and gating currents

1974 ◽  
Vol 7 (2) ◽  
pp. 179-209 ◽  
Author(s):  
Clay M. Armstrong
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Voltage Clamp ◽  
Complete Analysis ◽  
Current Phase ◽  
Ion Permeability ◽  
Gating Currents ◽  
Molecular Detail ◽  
Molecular Description ◽  
The Way

The current phase of axon physiology began with the invention of the voltage clamp by Cole (1949) and its use by Hodgkin & Huxley (1952d) to produce an astonishingly complete analysis of the ionic permeabilities that are responsible for the action potential. Their description did notcontain much in the way of molecular detail, and left open such questions as whether ions cross the membrane by way of pores or carriers, and the nature of the ‘gating‘ processes that increase ordecrease ion permeability in response to changes of the membrane potential. In the last few years our picture of the ionicchannels has grown considerably more tangible, though it still falls far short of a detailed molecular description. This article describes this sharpened picture and reviews the evidence for it. The viewpoint expressed is a very personal one, andno attempt has been made to review the literature of axonology comprehensively.

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