Studies of the cardiac-like action potential in crayfish giant axons induced by platinized tungsten metal electrodes

1987 ◽  
Vol 128 (1) ◽  
pp. 1-17
Author(s):  
L. A. Orr ◽  
E. M. Lieberman
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Giant Axon ◽  
Inward Rectification ◽  
Metal Electrodes ◽  
Dramatic Decrease ◽  
Functional Differences ◽  
Excitable Membranes ◽  
Delayed Rectification ◽  
Inward Currents

A lightly platinized tungsten (Pt-W) wire electrode, axially inserted into a crayfish giant axon, causes the development of cardiac-like action potentials with durations of up to 4 s. The plateau in membrane potential typically occurs within 10 min of the start of action potential elongation. The effect occurs without passing current through the Pt-W electrode and is temporally related to a dramatic decrease in intracellular pH (pHi). Such an effect cannot be induced by a decrease in pHi produced by equilibrating the axon with HCO3(−)-CO2 solution (pH6), and NH4Cl rebound or direct intracellular injection of PO4(3-) buffer (pH 4 X 5). Action potential elongation is accompanied by a block of delayed rectification and the possibility that inward rectification also develops cannot be ruled out. Plateau generation requires Na+ and Ca2+ inward currents as demonstrated by abolition of the plateau by [Na+]o or [Ca2+]o depletion or treatment with tetrodotoxin (TTX) or verapamil. The block of outward rectification by Pt-W requires external Na+ or Ca2+. Action potential elongation produced by 3,4-diaminopyridine is not sensitive to verapamil and the waveform is different from that produced by Pt-W. The data support the possibility that different classes of excitable membranes have similar channel populations and that the functional differences between them reside in the inhibitory or masking influences that are present in the microenvironments of the various membrane channels.

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.

Microelectrode Study of the Resting and Action Potentials of the Cockroach Giant Axon with Special Reference to the Role Played by the Nerve Sheath

1967 ◽  
Vol 47 (2) ◽  
pp. 357-373
Author(s):  
Y. PICHON ◽  
J. BOISTEL
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Maximum Rate ◽  
Diffusion Processes ◽  
Extracellular Fluid ◽  
Giant Axon ◽  
Resting Potential ◽  
Giant Axons ◽  
The Mean ◽  
Nerve Cords

1. The use of very fine-tipped and mechanically strong microelectrodes has allowed reliable recordings of resting and action potentials to be made in cockroach giant axons in sheathed and desheathed nerve cords. 2. When the microelectrode was withdrawn from a giant axon in an intact connective the first positive change in the potential from the resting level, was in most cases followed by a negative deflexion to the original zero level, the ‘sheath potential’. The values of this ‘sheath potential’ together with the resting potential, the action potential, the maximum rate of rise and maximum rate of fall of the action potential have been measured in three different salines. 3. In normal saline, resting potentials were lower in sheathed preparations (58·1 ± 55·4 mV.) than in desheathed ones (67·4 ± 6·2 mV.), whereas action potentials were higher in the former (103±5·9 mV.) than in the latter (85·9±4·6 mV.). 4. Elevation of K+ and Ca2+ concentrations in the saline to the haemolymph level resulted in a decrease of resting and action potentials in desheathed cords, to 57·3±5·3 mV. and 36·5±7·6 mV. respectively. No alterations in the membrane potentials were recorded in intact connectives bathed in this saline, the mean resting potential being 55·6±4·2 mV. and the mean action potential 107·9±6·0 mV. Local desheathing of the nerve cord led only to local disturbance of the resting and action potentials, thus indicating that diffusion processes along the extracellular spaces were very slow. 5. The use of a saline in which cation concentrations have been elevated to the extracellular level resulted in normal resting potentials (64·6±3·3 mV.) and action potentials (90·9±7·2 mV.) in desheathed cords, despite the relatively high potassium concentration (17·1 mM./l.). 6. Recordings of the maximum rates of rise and rates of fall showed that there was no significant modification in the shape of the action potential in these different experimental conditions. 7. The values of the ‘sheath potential’ were very variable from one impalement to another and it is suggested that this potential might be related to variations of the microelectrode tip potential bathed in different ionic solutions. 8. The low resting potentials and high action potentials of giant axons in intact nerve cords may result from an excess of inorganic cations in the extracellular fluid.

scholarly journals Calcium-activated conductance in skate electroreceptors: current clamp experiments.

1977 ◽  
Vol 69 (2) ◽  
pp. 121-143 ◽  
Author(s):  
W T Clusin ◽  
M V Bennett
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Calcium Current ◽  
Driving Force ◽  
Stimulus Strength ◽  
Current Clamp ◽  
Peak Voltage ◽  
Receptor Cells ◽  
Delayed Rectification ◽  
Calcium Permeability

When current clamped, skate electroreceptor epithelium produces large action potentials in response to stimuli that depolarize the lumenal faces of the receptor cells. With increasing stimulus strength these action potentials become prolonged. When the peak voltage exceeds about 140 mV the repolarizing phase is blocked until the end of the stimulus. Perfusion experiments show that the rising phase of the action potential results from an increase in calcium permeability in the lumenal membranes. Perfusion of the lumen with cobalt or with a zero calcium solution containing EGTA blocks the action potential. Perfusion of the lumen with a solution containing 10 mM Ca and 20 mM EGTA initially slows the repolarizing process at all voltages and lowers the potential at which it is blocked. With prolonged perfusion, repolarization is blocked at all voltages. When excitability is abolished by perfusion with cobalt, or with a zero calcium solution containing EGTA, no delayed rectification occurs. We suggest that repolarization during the action potential depends on an influx of calcium into the cytoplasm, and that the rate of repolarization depends on the magnitude of the inward calcium current. Increasingly large stimuli reduce the rate of repolarization by reducing the driving force for calcium, and then block repolarization by causing the lumenal membrane potential to exceed ECa. Changes in extracellular calcium affect repolarization in a manner consistent with the resulting change in ECa.

scholarly journals Some Effects of Calcium Ions on the Action Potential of Single Nodes of Ranvier

1964 ◽  
Vol 48 (1) ◽  
pp. 113-127 ◽  
Author(s):  
Werner Ulbricht
Keyword(s):  
Action Potential ◽  
Calcium Ions ◽  
Refractory Period ◽  
Qualitative Agreement ◽  
Action Potentials ◽  
Outward Current ◽  
Nerve Fibers ◽  
Current Pulses ◽  
Delayed Rectification ◽  
Voltage Clamp Analysis

Action potentials of single frog nerve fibers were recorded with the air-gap method in "low Ca" (0.26 mM) and "high Ca" (4.2 mM) solutions and compared to spikes in normal Ringer's (1.05 mM Ca). On increasing (Ca)o the action potentials became shorter, the "knee" during the falling phase as well as the threshold for abolition moved to internal potentials more positive, and the spike recovery during the relative refractory period was faster. Outward current pulses applied during an action potential affected its configuration more in low Ca than in high Ca. The onset of the delayed rectification (in the absence of Na) was found faster in high Ga. After-potentials during anelectrotonus declined more rapidly in high Ca than in low Ca. The results are compared primarily with the voltage-clamp analysis of Ca effects on squid axons and satisfactory qualitative agreement is reached.

Properties of Action Potentials from Insect Motor Nerve Fibres

1970 ◽  
Vol 53 (2) ◽  
pp. 299-316 ◽  
Author(s):  
K. G. PEARSON ◽  
R. B. STEIN ◽  
S. K. MALHOTRA
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Motor Nerve ◽  
Fibre Diameter ◽  
Extracellular Recording ◽  
Membrane Properties ◽  
Nerve Fibres ◽  
Functional Differences ◽  
Root Relation ◽  
Motor Nerves

1. The properties of nerve action potentials in small insect motor nerves were studied using extracellular recording electrodes. 2. A length of nerve was lifted out of solution and recordings were made with respect to the solution either from an intact nerve (triphasic recording) or from near a cut end of the nerve (monophasic recording). 3. In a cockroach nerve, the number of spontaneously active fibres was small enough that corresponding nerve fibres could be identified in each preparation by their action potential amplitude and their pattern of activity. Under controlled conditions, the absolute amplitudes of either monophasic or triphasic records were reproducible and could be used to calculate fibre diameter. The calculations were confirmed from histological sections of the nerve. 4. Conduction velocity varied approximately as the 0.78 power of fibre diameter in a cockroach nerve and as 0.7 power of fibre diameter in a locust nerve. These values are considerably larger than the square root relation predicted if membrane properties are independent of fibre diameter. 5. Membrane properties probably vary with fibre diameter since the action potential duration increases dramatically for fibres below 5 µ in diameter. 6. For the cockroach nerve systematic structural differences between fibres of different sizes are also seen with the electron microscope and the relation of these to the functional differences is considered.

Helping students to understand that outward currents depolarize cells.

1999 ◽  
Vol 276 (6) ◽  
pp. S62
Author(s):  
M Stewart
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Action Potentials ◽  
Building Blocks ◽  
Resting Potential ◽  
Potassium Ions ◽  
General Statement ◽  
Outward Currents ◽  
Excitable Membranes ◽  
A Cell

The physiology of excitable membranes is a fundamental topic in neuroscience and physiology courses at graduate and undergraduate levels. From the building blocks of ionic gradients and membrane channels whose permeability is selective and variable, we build the concepts of resting potential, action potential, and propagation in neurons and muscle fibers. Many students have an intuitive understanding of the movements of ions and the associated changes in membrane potential. For example, potassium ions leaving a cell through potassium-selective channels become unbalanced positive charges on the outside of the cell (and leave unbalanced negative charges on the inside), thus producing a potential across the membrane with the inside negative with respect to the outside. Later, when we discuss the local circuit currents that underlie propagation or the basis for extracellular stimulation, we make the general statement that "outward currents depolarize cells." Students respond with utter disbelief. Two simple additions to a discussion of membranes are suggested that permit the formulation of a consistent set of rules that apply to everything from the resting and action potentials of nerve and muscle through synaptic potentials and stimulation techniques.

scholarly journals Neurogenic substance P—influences on action potential production in afferent neurons of the kidney?

2021 ◽  
Vol 473 (4) ◽  
pp. 633-646
Author(s):  
Kristina Rodionova ◽  
Karl F. Hilgers ◽  
Peter Linz ◽  
Johannes Schätzl ◽  
Giulia Raschke ◽  
...  
Keyword(s):  
Substance P ◽  
Action Potential ◽  
Action Potentials ◽  
Current Injection ◽  
Renal Nerves ◽  
Drg Neurons ◽  
Potential Production ◽  
Current Clamp Mode ◽  
Inward Currents ◽  
Dependent Mechanism

AbstractWe recently showed that a substance P (SP)–dependent sympatho-inhibitory mechanism via afferent renal nerves is impaired in mesangioproliferative nephritis. Therefore, we tested the hypothesis that SP released from renal afferents inhibits the action potential (AP) production in their dorsal root ganglion (DRG) neurons. Cultured DRG neurons (Th11-L2) were investigated in current clamp mode to assess AP generation during both TRPV1 stimulation by protons (pH 6) and current injections with and without exposure to SP (0.5 µmol) or CGRP (0.5 µmol). Neurons were classified as tonic (sustained AP generation) or phasic (≤ 4 APs) upon current injection; voltage clamp experiments were performed for the investigation of TRPV1-mediated inward currents due to proton stimulation. Superfusion of renal neurons with protons and SP increased the number of action potentials in tonic neurons (9.6 ± 5 APs/10 s vs. 16.9 ± 6.1 APs/10 s, P < 0.05, mean ± SD, n = 7), while current injections with SP decreased it (15.2 ± 6 APs/600 ms vs. 10.2 ± 8 APs/600 ms, P < 0.05, mean ± SD, n = 29). Addition of SP significantly reduced acid-induced TRPV1-mediated currents in renal tonic neurons (− 518 ± 743 pA due to pH 6 superfusion vs. − 82 ± 50 pA due to pH 6 with SP superfusion). In conclusion, SP increased action potential production via a TRPV1-dependent mechanism in acid-sensitive renal neurons. On the other hand, current injection in the presence of SP led to decreased action potential production. Thus, the peptide SP modulates signaling pathways in renal neurons in an unexpected manner leading to both stimulation and inhibition of renal neuronal activity in different (e.g., acidic) environmental contexts.

Axonal Adaptations to Osmotic and Ionic Stress in an Invertebrate Osmoconformer (Mercierella Enigmatica Fauvel): II. Effects of Ionic Dilution on the Resting and Action Potentials

1978 ◽  
Vol 76 (1) ◽  
pp. 205-219
Author(s):  
J. A. BENSON ◽  
J. E. TREHERNE
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Prolonged Exposure ◽  
Giant Axon ◽  
Sodium Concentration ◽  
Ionic Concentration ◽  
Osmotic Concentration ◽  
Bathing Medium ◽  
Axon Membrane ◽  
Wide Range

The giant axon of this extreme euryhaline osmoconformer possess an unusual ability to produce action potentials of large amplitude over a wide range of ionic dilution when constant osmotic concentration is maintained by the addition of mannitol to the bathing medium. Ionic dilution under these circumstances causes a decline in the overshoot of the action potential (resulting largely from reduction in [Na+]0) and an appreciable axonal hyperpolarization (primarily as a result of decrease in [K+]0). This hyperpolarization tends to compensate for the reduction in the extent of the overshoot and so maintains the amplitude of the sodium-mediated action potentials during isosmotic dilution of the bathing medium. The axonal hyperpolarization also appears to reduce sodium inactivation so as to maintain a rapid rate of rise of the action potential despite drastic reduction in the ionic concentration of the bathing medium. Prolonged exposure to reduced ionic concentrations appears to induce a ouabain sensitive reduction in intracellular sodium concentration which increases the sodium gradient across the axon membrane during isosmotic dilution of the external medium.

A comparison of propagated action potentials from tropical and temperate squid axons: different durations and conduction velocities correlate with ionic conductance levels

2002 ◽  
Vol 205 (12) ◽  
pp. 1819-1830 ◽  
Author(s):  
Joshua J. C. Rosenthal ◽  
Francisco Bezanilla
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Thermal Environment ◽  
Giant Axon ◽  
Temperature Adaptation ◽  
Membrane Action ◽  
Decay Times ◽  
Conduction Velocities ◽  
Loligo Pealei

SUMMARYTo determine which physiological properties contribute to temperature adaptation in the squid giant axon, action potentials were recorded from four species of squid whose habitats span a temperature range of 20°C. The environments of these species can be ranked from coldest to warmest as follows: Loligo opalescens&gt;Loligo pealei&gt;Loligo plei&gt;Sepioteuthis sepioidea. Action potential conduction velocities and rise times,recorded at many temperatures, were equivalent for all Loligospecies, but significantly slower in S. sepioidea. By contrast, the action potential's fall time differed among species and correlated well with the thermal environment of the species (`warmer' species had slower decay times). The biophysical underpinnings of these differences were examined in voltage-clamped axons. Surprisingly, no differences were found between the activation kinetics or voltage-dependence of Na+ and K+currents. Conductance levels, however, did vary. Maximum Na+conductance (gNa) in S. sepiodea was significantly less than in the Loligo species. K+ conductance (gK) was highest in L. pealei, intermediate in L. plei and smallest in S. sepiodea. The time course and magnitude of gK and gNa were measured directly during membrane action potentials. These data reveal clear species-dependent differences in the amount of gK and gNa recruited during an action potential.

Current-Voltage Relations in the Isolated Giant Axon of the Cockroach Under Voltage-Clamp Conditions

1967 ◽  
Vol 47 (2) ◽  
pp. 343-355
Author(s):  
Y. PICHON ◽  
J. BOISTEL
Keyword(s):  
Action Potentials ◽  
Outward Current ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Giant Axon ◽  
Inward Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Inward Currents ◽  
Na Ions

1. An experimental method of recording and controlling the membrane potential of a small area of the membrane of the cockroach giant axon is described. 2. The recorded action potentials were essentially similar to those previously recorded by other methods. 3. The membrane currents resemble those reported for the squid axon, the node of Ranvier in frog nerve and the lobster giant axon. 4. Small cathodal polarizations gave only small outward currents; larger depolarizations (10-100 mV.) gave an initial inward current which changed into a delayed outward current. 5. The initial inward current attained a maximum with depolarizing pulses of 40-50 mV. and showed a reversed, outward, flow of about 100 mV. 6. Delayed outward currents increased continuously with increasing impulse voltage. 7. The initial inward current was larger when the pulse was preceded by an hyperpolarizing prepulse. 8. It is concluded that, although the early inward currents were in all probability related to Na+ ions and the delayed outward currents to K+ ions, the possible participation of Ca2+ and Cl- ions to the ionic currents cannot be excluded.

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