scholarly journals Sodium-Calcium Action Potential Associated with Contraction in the Heliozoan Actinocoryne Contractilis

1986 ◽  
Vol 122 (1) ◽  
pp. 177-192 ◽  
Author(s):  
COLETTE FEBVRE-CHEVALIER ◽  
ANDRÉ BILBAUT ◽  
QUENTIN BONE ◽  
JEAN FEBVRE
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Receptor Potential ◽  
Resting Membrane Potential ◽  
Mechanical Stimuli ◽  
Free Solution ◽  
Sodium Calcium ◽  
Rapid Action ◽  
A Minor ◽  
Calcium Action Potential

The electrophysiology of the contractile protozoan Actinocoryne contractilis was studied with conventional intracellular recording techniques. Resting membrane potential (−78 mV, s.d. = 8, N = 18) was dependent upon external K+. Rapid action potentials (overshoot up to 50 mV) were evoked either by mechanical stimulation or by current injection. Graded membrane depolarizations induced by graded mechanical stimuli correspond to receptor potentials. The receptor potential was mainly Na+-dependent; the action potential was also mainly Na+-dependent, but involved a minor Ca2+-dependence. The two components of the action potential could be separated in Ca2+-free solution containing EGTA (1 mmol l−1), in low-Na+ solutions or by the addition of Co2+. The repolarizing phase of the action potential was sensitive to TEA ions and to 4-aminopyridine (4-AP). Action potentials were followed in 10–20 ms by a rapid all-or-none contraction of the axopods and stalk. Contraction was blocked in Ca2+-free solution containing EGTA and by Co2+, which suggests a requirement of external Ca2+ for this event. Contraction was also abolished by 4-AP.

scholarly journals Receptor Response in Venus's Fly-Trap

1965 ◽  
Vol 49 (1) ◽  
pp. 117-129 ◽  
Author(s):  
Stuart L. Jacobson
Keyword(s):  
Action Potential ◽  
Mechanical Stimulation ◽  
Action Potentials ◽  
Natural Extension ◽  
Receptor Potential ◽  
Mechanical Stimuli ◽  
Dionaea Muscipula ◽  
Receptor Response ◽  
Current Measuring ◽  
Stimulation Of

The insect-trapping movement of the plant Dionaea muscipula (Venus's fly-trap) is mediated by the stimulation of mechanosensory hairs located on the surface of the trap. It is known that stimulation of the hairs is followed by action potentials which are propagated over the surface of the trap. It has been reported that action potentials always precede trap closure. The occurrence of non-propagated receptor potentials is reported here. Receptor potentials always precede the action potentials. The receptor potential appears to couple the mechanical stimulation step to the action potential step of the preying sequence. Receptor potentials elicited by mechanical stimulation of a sensory hair were measured by using the hair as an integral part of the current-measuring path. The tip of the hair was cut off exposing the medullary tissue; this provided a natural extension of the measuring electrode into the receptor region at the base of the hair. A measuring pipette electrode was slipped over the cut tip of the hair. Positive and negative receptor potentials were measured. Evidence is presented which supports the hypothesis that the positive and negative receptor potentials originate from independent sources. An analysis is made of (a) the relation of the parameters of mechanical stimuli to the magnitude of the receptor potential, and (b) the relation of the receptor potentials to the action potential. The hypothesis that the positive receptor potential is the generator of the action potential is consistent with these data.

Contribution of Nav1.8 Sodium Channels to Action Potential Electrogenesis in DRG Neurons

2001 ◽  
Vol 86 (2) ◽  
pp. 629-640 ◽  
Author(s):  
Muthukrishnan Renganathan ◽  
Theodore R. Cummins ◽  
Stephen G. Waxman
Keyword(s):  
Action Potential ◽  
Sodium Channels ◽  
Action Potentials ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Drg Neurons ◽  
Significant Difference ◽  
Steady State Inactivation ◽  
Current Threshold

C-type dorsal root ganglion (DRG) neurons can generate tetrodotoxin-resistant (TTX-R) sodium-dependent action potentials. However, multiple sodium channels are expressed in these neurons, and the molecular identity of the TTX-R sodium channels that contribute to action potential production in these neurons has not been established. In this study, we used current-clamp recordings to compare action potential electrogenesis in Nav1.8 (+/+) and (−/−) small DRG neurons maintained for 2–8 h in vitro to examine the role of sodium channel Nav1.8 (α-SNS) in action potential electrogenesis. Although there was no significant difference in resting membrane potential, input resistance, current threshold, or voltage threshold in Nav1.8 (+/+) and (−/−) DRG neurons, there were significant differences in action potential electrogenesis. Most Nav1.8 (+/+) neurons generate all-or-none action potentials, whereas most of Nav1.8 (−/−) neurons produce smaller graded responses. The peak of the response was significantly reduced in Nav1.8 (−/−) neurons [31.5 ± 2.2 (SE) mV] compared with Nav1.8 (+/+) neurons (55.0 ± 4.3 mV). The maximum rise slope was 84.7 ± 11.2 mV/ms in Nav1.8 (+/+) neurons, significantly faster than in Nav1.8 (−/−) neurons where it was 47.2 ± 1.3 mV/ms. Calculations based on the action potential overshoot in Nav1.8 (+/+) and (−/−) neurons, following blockade of Ca2+ currents, indicate that Nav1.8 contributes a substantial fraction (80–90%) of the inward membrane current that flows during the rising phase of the action potential. We found that fast TTX-sensitive Na+ channels can produce all-or-none action potentials in some Nav1.8 (−/−) neurons but, presumably as a result of steady-state inactivation of these channels, electrogenesis in Nav1.8 (−/−) neurons is more sensitive to membrane depolarization than in Nav1.8 (+/+) neurons, and, in the absence of Nav1.8, is attenuated with even modest depolarization. These observations indicate that Nav1.8 contributes substantially to action potential electrogenesis in C-type DRG neurons.

Isolated Giant Smooth Muscle Fibres in Beroe Ovata: Ionic Dependence of Action Potentials Reveals Two Distinct Types of Fibre

1988 ◽  
Vol 135 (1) ◽  
pp. 343-362 ◽  
Author(s):  
ANDRÉ BILBAUT ◽  
ROBERT W. MEECH ◽  
MARI-LUZ HERNANDEZ-NICAISE
Keyword(s):  
Smooth Muscle ◽  
Action Potential ◽  
Action Potentials ◽  
Marine Invertebrate ◽  
The Body ◽  
Fibre Types ◽  
Resting Membrane Potential ◽  
Muscle Fibres ◽  
Beroe Ovata ◽  
Radial Muscle

1. The ionic dependence of action potentials evoked in giant smooth muscle fibres isolated by enzymatic digestion from the body wall of the marine invertebrate Beroe ovata (Ctenophora) has been investigated using conventional electrophysiological techniques. 2. Differences were observed in the two fibre types studied. The resting membrane potential was −60 ± 1.35 mV (N = 25) in longitudinal muscle fibres and −66 ±1.37 mV (N=32) in radial fibres. Action potentials had a short plateau in longitudinal fibres but not in radial fibres. 3. The action potential overshoot of both fibre types was decreased in Ca2+-free artificial sea water (ASW). In Na+-deficient ASW, action potentials could not be generated in radial fibres and showed a reduced overshoot in longitudinal fibres. 4. Tetrodotoxin (10−5moll−5) added to ASW or Ca2+-free ASW did not affect the action potentials of either type of fibre. 5. Action potentials of both fibres were partially blocked by Co2+ (20–50 mmoll−1) or Cd2+ (l-2mmoll−1). Action potentials of longitudinal fibres in Na+-deficient ASW were abolished by Co2+ (20mmoll−1). In Ca2+-free ASW, the ction potential overshoots of both sets of fibres were restored following the addition of Sr2+ or Ba2+. In longitudinal fibres, Sr2+ increased the duration of the action potential plateau. In both longitudinal and radial muscle fibres, Ba2+ prolonged the action potential. 6. In longitudinal fibres exposed to tetraethylammonium chloride (TEAC1) or 4-aminopyridine (4AP), the action potential was slightly prolonged. In these fibres, TEA+ or 4AP added to Ca2+-free ASW induced only a long-lasting depolarizing plateau. In radial fibres, the action potential duration was slightly increased in the presence of TEA+; it was unaffected by 4AP. In Ca2+-free ASW, TEA+ and 4AP induced an oscillating membrane response which appeared to be dependent on the intensity of the injected current pulse. 7. It is concluded that (a) there are significant differences between the action potentials of longitudinal and radial muscle fibres but that both are dependent on Na+ and Ca2+, (b) in longitudinal fibres, a Ca2+-activated K+ conductance and a TEA+-sensitive voltage-activated K+ conductance contribute to the repolarizing phase of the action potential, the former being predominant, (c) in radial fibres, the repolarizing phase of action potentials probably involves different membrane K+ conductances among which is a TEA+-sensitive K+ conductance.

Excitable Membrane Properties of Neurons

2020 ◽  
Author(s):  
Leonard K. Kaczmarek
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Cell Biology ◽  
Neuronal Firing ◽  
Membrane Properties ◽  
Potassium Ions ◽  
Single Action ◽  
Sodium Calcium ◽  
Different Types ◽  
Order Of Magnitude

The intrinsic electrical properties of neurons are extremely varied. For example, the width of action potentials in different neurons varies by more than an order of magnitude. In response to prolonged stimulation, some neurons generate repeated action potential hundreds of times a second, while others fire only a single action potential or adapt very rapidly. These differences result from the expression of different types of ion channels in the plasma membrane. The dominant channels that shape neuronal firing patterns are those that are selective for sodium, calcium, and potassium ions. This chapter provides a brief overview of the biophysical properties of each of these classes of channel, their role in shaping the electrical personality of a neuron, and how interactions of these channels with cytoplasmic factors shape the overall cell biology of a neuron.

scholarly journals The Effect of Aconitine on the Giant Axon of the Squid

1964 ◽  
Vol 47 (4) ◽  
pp. 719-733 ◽  
Author(s):  
W. H. Herzog ◽  
R. M. Feibel ◽  
S. H. Bryant
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Action Potentials ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Repetitive Stimulation ◽  
Resting Membrane Potential ◽  
Sustained Activity ◽  
Frequency Of Stimulation ◽  
Sodium And Potassium

In the giant axon of Loligo pealii, "aconitine potent" Merck added to the bath (10-7 to 1.25 x 10-6 gm/ml) (a) had no effect on resting membrane potential, membrane resistance and rectification, membrane response to subthreshold currents, critical depolarization, or action potential, but (b) on repetitive stimulation produced oscillations of membrane potential after the spike, depolarization, and decrease of membrane resistance. The effect sums with successive action potentials; it increases with concentration of aconitine, time of exposure, and frequency of stimulation. When the oscillations are large enough and the membrane potential is 51.6 ± SD 1.5 mv a burst of self-sustained activity begins; it usually lasts 20 to 70 sec. and at its end the membrane potential is 41.5 ± SD 1.9 mv. Repolarization occurs with a time constant of 2.5 to 11.1 min. Substitution of choline for external sodium after a burst hyperpolarizes the membrane to -70 mv, and return to normal external sodium depolarizes again beyond the resting membrane potential. The effect of aconitine on the membrane is attributed to an increase of sodium and potassium or chloride conductances following the action potential.

Transmembrane potential and force of contraction of the normal and potassium-deficient human atrial tissue in vitro

1969 ◽  
Vol 47 (12) ◽  
pp. 1015-1024 ◽  
Author(s):  
Kailash Prasad
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Terminal Phase ◽  
Free Solution ◽  
Force Of Contraction ◽  
Pacemaker Cells ◽  
Atrial Tissue ◽  
Action Potential Plateau ◽  
Potential Plateau

The characteristics of the simultaneously recorded action potential (AP) and contraction of isolated atrial tissue of human heart were studied in normal and in potassium-free solutions. Two types of action potentials associated with characteristic contractions were observed. Pacemaker types of action potentials with two humps in the plateau were observed in spontaneously beating atria and they were associated with triple contractions. A non-pacemaker type of action potential was found in quiescent fibers when the preparation was driven electrically; this resulted in single peak contraction. The sizes of the resting and action potentials of pacemaker cells were lower, while those of action potential duration in all types of cells were higher than those reported in other mammals. When spontaneously beating atrial pieces were exposed to a potassium-free solution there was a shortening of the action potential plateau and lengthening of the terminal phase of repolarization associated with the development of the first hump into a slow spike. The shortening of the action potential plateau associated with an increase in the force of contraction was also observed in electrically stimulated muscles in KCl-free solution.

scholarly journals Dynamic Current Clamp Experiments Define the Functional Roles of IK1 and Ito,f in Human Induced Pluripotent Stem Cell Derived Cardiomyocytes

2017 ◽  
Author(s):  
Scott B. Marrus ◽  
Steven Springer ◽  
Eric Johnson ◽  
Rita J. Martinez ◽  
Edward J. Dranoff ◽  
...  
Keyword(s):  
Stem Cell ◽  
Action Potential ◽  
Action Potentials ◽  
Pluripotent Stem Cell ◽  
Phase 1 ◽  
Induced Pluripotent Stem Cell ◽  
Resting Membrane Potential ◽  
Current Clamp ◽  
Human Cardiomyocytes ◽  
Induced Pluripotent

AbstractThe transient outward potassium current (Ito) plays a key, albeit incompletely defined, role in cardiomyocyte physiology and pathophysiology. In light of the technical challenges of studying adult human cardiomyocytes, this study examines the use of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) as a system which potentially preserves the native cellular milieu of human cardiomyocytes. ISPC-CMs express a robust Ito with slow recovery kinetics and fail to express the rapidly recovering Ito,f which is implicated in human disease. Overexpression of the accessory subunit KChIP2 (which is not expressed in iPSC-CMs) resulted in restoration of a rapid component of recovery. To define the functional role of Ito, dynamic current clamp was used to introduce computationally modeled currents into iPSC-CMs while recording action potentials. However, iPSC-CMs exhibit action potentials with multiple immature physiological properties, including slow upstroke velocity, heterogeneous action potential waveforms, and the absence of a phase 1 notch, thus potentially limiting the utility of these cells as a model of adult cardiomyocytes. Importantly, the introduction of modeled inwardly rectified current (IK1) ameliorated these immature properties by restoring a hyperpolarized resting membrane potential. In this context of normalized action potential morphologies, dynamic current clamp experiments introducing Ito,f demonstrated that there is significant cell-to-cell heterogeneity and that the functional effect of Ito,f is highly sensitive to the action potential plateau voltage in each cell.

scholarly journals The mechanosensitive ion channel TRAAK is localized to the mammalian node of Ranvier

2019 ◽  
Author(s):  
Stephen G. Brohawn ◽  
Weiwei Wang ◽  
Jürgen R. Schwarz ◽  
Annie Handler ◽  
Ernest B. Campbell ◽  
...  
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Polyclonal Antibodies ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Resting Membrane Potential ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers ◽  
Behavioral Studies ◽  
Mechanosensitive Ion Channel

ABSTRACTTRAAK is a membrane tension-activated K+ channel that has been associated through behavioral studies to mechanical nociception. We used specific monoclonal antibodies in mice to show that TRAAK is localized exclusively to nodes of Ranvier, the action potential propagating elements of myelinated nerve fibers. Approximately 80 percent of myelinated nerve fibers throughout the central and peripheral nervous system contain TRAAK in an all-nodes or no-nodes per axon fashion. TRAAK is not observed at the axon initial segment where action potentials are first generated. We used polyclonal antibodies, the TRAAK inhibitor RU2 and node clamp amplifiers to demonstrate the presence and functional properties of TRAAK in rat nerve fibers. TRAAK contributes to the ‘leak’ K+ current in mammalian nerve fiber conduction by hyperpolarizing the resting membrane potential, thereby increasing Na+ channel availability for action potential propagation. Mechanical gating in TRAAK might serve a neuroprotective role by counteracting mechanically-induced ectopic action potentials. Alternatively, TRAAK may open in response to mechanical forces in the nodal membrane associated with depolarization during saltatory conduction and thereby contribute to repolarization of the node for subsequent spikes.

Effects of temperature on cardiac transmembrane potentials in hibernation

1976 ◽  
Vol 230 (2) ◽  
pp. 403-409 ◽  
Author(s):  
HK Jacobs ◽  
FE South
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Papillary Muscle ◽  
Action Potentials ◽  
Resting Membrane Potential ◽  
Prolonged Action ◽  
Transmembrane Potentials ◽  
Effects Of Temperature ◽  
And Control ◽  
Potential Parameters

Resting and action potential parameters were measured from papillary muscle isolated from hibernating and control hamsters and from rats. The temperature range of the study was 12-38 degrees C. The decrease in resting membrane potential (Em) with decreasing temperature was significantly less in the hibernation preparations (HH), down to 20 degrees C, than in either the control hamsters or rats. Below 20 degrees C the declines in Em of all preparations were indistinguishable. Action potential magnitude was adequately maintained in HH to 12 degrees C while both control hamster and rat action potentials declined markedly as temperatures were reduced. Both types of hamster preparations showed greatly prolonged action potentials with reduced temperatures as contrasted to a limited prolongation of rat action potentials. The data are suggestive of a membrane modication in hibernation.

Augmentation and suppression of action potentials by estradiol in the myometrium of pregnant rat

1999 ◽  
Vol 77 (6) ◽  
pp. 447-453 ◽  
Author(s):  
Yoshihito Inoue ◽  
Koji Okabe ◽  
Hiroyuki Soeda
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Single Cells ◽  
Muscle Cells ◽  
Enzymatic Digestion ◽  
Resting Membrane Potential ◽  
Spike Generation ◽  
Pregnant Rat ◽  
Outward Currents ◽  
Spontaneous Action

The purpose of this study was to investigate the actions of estradiol on spontaneous and evoked action potentials in the isolated longitudinal smooth muscle cells of the pregnant rat. Single cells were obtained by enzymatic digestion from pregnant rat longitudinal myometrium. Action potentials and currents were recorded by whole-cell current-clamp and voltage-clamp methods, respectively. The acute effects of 17β-estradiol on action potentials and inward and outward currents were investigated. The following results were obtained. The average resting membrane potential of single myometrial cells was -54 mV (n = 40). In many cells, an electrical stimulation evoked a membrane depolarization, and action potentials were superimposed on the depolarization. In some cells, spontaneous action potentials were observed. Estradiol (30 µM) slightly depolarized the membrane (ca. 5 mV) and attenuated the generation of action potentials by reducing the frequency and amplitude of the spikes. Afterhyperpolarization was also attenuated by estradiol (30 µM). On the other hand, in 5 of 35 cells, estradiol increased the first spike amplitude and action potential duration, while frequency of the spike generation and afterhyperpolarization were inhibited. In voltage-clamped muscle cells, estradiol inhibited both inward and outward currents. Acute inhibition or augmentation of spike generation by estradiol is due to the balance of inhibition of inward and outward currents. Inhibition of both currents also prevented afterhyperpolarization, causing potential-dependent block of Ca spikes.Key words: estradiol, progesterone, rat myometrium, action potential, channel current.

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