scholarly journals ELECTRIC IMPEDANCE OF NITELLA DURING ACTIVITY

1938 ◽  
Vol 22 (1) ◽  
pp. 37-64 ◽  
Author(s):  
Kenneth S. Cole ◽  
Howard J. Curtis
Keyword(s):  
Action Potential ◽  
Current Flow ◽  
Short Circuit ◽  
Complex Impedance ◽  
Wheatstone Bridge ◽  
Membrane Resistance ◽  
Cell Axis ◽  
Excitation Wave ◽  
Water Plant ◽  
Membrane Changes

The changes in the alternating current impedance which occur during activity of cells of the fresh water plant Nitella have been measured with the current flow normal to the cell axis, at eight frequencies from 0.05 to 20 kilocycles per second, and with simultaneous records of the action potential under the impedance electrodes. At each frequency the resting cell was balanced in a Wheatstone bridge with a cathode ray oscillograph, and after electrical stimulation at one end of the cell, the changes in the complex impedance were determined from the bridge unbalance recorded by motion pictures of the oscillograph figure. An extension of the previous technique of interpretation of the transverse impedance shows that the normal membrane capacity of 0.9 µf./cm.2 decreases about 15 per cent without change of phase angle, while the membrane resistance decreases from 105 ohm cm.2 to about 500 ohm cm.2 during the passage of the excitation wave. This membrane change occurs during the latter part of the rising phase of the action potential, and it is shown that the membrane electromotive force remains unchanged until nearly the same time. The part of the action potential preceding these membrane changes is probably a passive fall of potential ahead of a partial short circuit.

scholarly journals Membrane Characteristics of the Canine Papillary Muscle Fiber

1969 ◽  
Vol 54 (6) ◽  
pp. 765-781 ◽  
Author(s):  
Yasuzi Sakamoto
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Time Constant ◽  
Papillary Muscle ◽  
Time Course ◽  
Current Flow ◽  
Membrane Resistance ◽  
Muscle Membrane ◽  
Spatial Decay ◽  
Similar Time

Passive and active responses to intracellular and extracellular stimulation were studied in the canine papillary muscle. The electrotonic potential produced by extracellular polarization with the partition chamber method fitted the time course and the spatial decay expected from the cable theory (the time constant, 3.3 msec; the space constant, 1.2 mm). Contrariwise, spatial decay of the electrotonic potentials produced by intracellular polarization was very short and did not fit the decay curve expected for a simple cable, although only a small difference of time course in the electrotonic potentials produced by intracellular and extracellular polarizations was observed. A similar time course might result from the fact that when current flow results from intracellular polarization, the input resistance is less dependent on the membrane resistance. The foot of the propagated action potential rose exponentially with a time constant of 1.1 msec and a conduction velocity of 0.68 m/sec. The membrane capacity was calculated from the time constant of the foot potential and the conduction velocity to be 0.76 µF/cm2. The responses of the papillary muscle membrane to intracellular stimulation differed from those to extracellular stimulation applied with the partition method in the following ways: higher threshold potential, shorter latency for the active response, linearity of the current-voltage relationship, and no reduction in the membrane resistance at the crest of the action potential during current flow.

An electrically mediated inhibition in goldfish medulla

1975 ◽  
Vol 38 (2) ◽  
pp. 452-471 ◽  
Author(s):  
H. Korn ◽  
D. S. Faber
Keyword(s):  
Action Potential ◽  
Time Course ◽  
Current Flow ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Neuronal Population ◽  
M Cell ◽  
Neuronal Membranes ◽  
Cathodal Current ◽  
Medullary Neurons

1. Passive hyperpolarizing potentials (PHPs) have been recorded intracellularly from goldfish medullary neurons in the vicinity of the Mauthner cell (M-cell). They are evoked when this cell is activated antidromically by stimulation of the spinal cord, and orthodromically via the ipsilateral eighth nerve; when appropriately timed they block or delay spikes induced both directly and transsynaptically. 2. Since the PHPs and the M-cell spike have the same latency, time course, and all-or-none character, they cannot be generated by chemically mediated synaptic transmission. This conclusion is further supported by the evidence that PHP amplitude and time course are independent of membrane potential. 3. The analysis of the mechanism underlying PHP generation has been based on the hypothesis that they are brought about by the extracellular currents flowing to the axon cap during an M-cell action potential. Specifically, it was postulated that some of this current is channeled back to the axon cap region intracellularly through processes of PHP-exhibiting neurons, and that these cells are passively hyperpolarized by the associated inward transmembrane current flow. This model would require that PHP-exhibiting neurons send processes into the axon cap. This hypothesis is confirmed by the following: a) When the PHP is timed to occur during the conductance increase associated with a spike after hyperpolarization, it is reduced, as would be expected for a passive current flow across a membrane resistance. b) PHPs are not found in all medullary neurons in the vicinity of the M-cell, but rather in a specific neuronal population. c) PHP-exhibiting neurons have been identified following Procion yellow injections; as predicted, they issue one process, presumably the axon, which projects toward the M-cell axon cap area. d) The PHP can be stimulated by passing a cathodal current from a microelectrode located in the axon cap; it is not mimicked when the cathodal electrode is moved outside this region. The currents necessary to mimic a PHP are comparable to the estimated current flowing back to the axon cap during an M-cell action potential. 4. The input resistance of PHP-exhibiting neurons is in the range of 4 M alpha, and their estimated specific membrane resistance is in the range of 900-2,000 alpha-cm-2, which is not an unusually low value for neuronal membranes. By contrast, the intracellular channeling of current during a PHP can rather be attributed to a high extracellular tissue resistance within the axon cap, which was found to be at least 2.5 times that of the surrounding medullary tissue..

scholarly journals Thermal Analysis of Heat Distribution in Busbars during Rated Current Flow in Low-Voltage Industrial Switchgear

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2427
Author(s):  
Michał Szulborski ◽  
Sebastian Łapczyński ◽  
Łukasz Kolimas
Keyword(s):  
Structural Changes ◽  
Heat Dissipation ◽  
Current Flow ◽  
Low Voltage ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Coupled Analysis ◽  
Precise Representation ◽  
Transient Thermal ◽  
Halogen Free

The manuscript presents advanced coupled analysis: Maxwell 3D, Transient Thermal and Fluent CFD, at the time of a rated current occurring on the main busbars in the low-voltage switchgear. The simulations were procured in order to aid the design process of such enclosures. The analysis presented the rated current flow in the switchgear busbars, which allowed determining their temperature values. The main assumption of the simulation was measurements of temperature rise during rated current conditions. Simulating such conditions is a valuable asset in order to design better solutions for energy distribution gear. The simulation model was a precise representation of the actual prototype of the switchgear. Simulations results were validated by experimental research. The heat dissipation in busbars and switchgear housing through air convection was presented. The temperature distribution for the insulators in the rail bridge made of fireproof material was considered: halogen-free polyester. The results obtained during the simulation allowed for a detailed analysis of switchgear design and proper conclusions in practical and theoretical aspects. That helped in introducing structural changes in the prepared prototype of the switchgear at the design and construction stages. Deep analysis of the simulation results allowed for the development concerning the final prototype of the switchgear, which could be subjected to the full type tests. Additionally, short-circuit current simulations were procured and presented.

scholarly journals Further Observations on the Regulation of KCl ABSORPTION ACROSS LOCUST RECTUM

1985 ◽  
Vol 116 (1) ◽  
pp. 153-167
Author(s):  
J. W. HANRAHAN ◽  
J. E. PHILLIPS
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Open Circuit ◽  
High K ◽  
K Concentration ◽  
K Permeability

1. Electrophysiological and tracer flux techniques were used to studyregulation of KC1 reabsorption across locust recta. Physiologically high K+levels (100 mmolI−1) on the lumen side stimulated net 36Cl flux and reduced the theoretical energy cost of anion transport under open-circuit conductions. 2. The stimulation of short-circuit current (Ibc i.e. active C− absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca2+. Stimulations of Ibc were greatly enhanced in the presence of theophylline, indicating that the rate of synthesis of cAMP is increased by CC extracts. High CC levels lowered transepithelial resistance (Rt), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl− absorption and counter-ion (K+) permeability. 3. High mucosal osmolarity or K+ concentration decreased Ibc and caused a disproportionately large increase in Rt, consistent with a decrease in theshunt (K+) conductance. Measurements of relative mucosal-to-serosal membrane resistance confirmed that high mucosal K+ levels reduced apical membrane conductance. Lowering mucosal pH to values observed in vivo atthe end of resorptive cycles also inhibited Ibc, apparently without affecting K+ permeability.

Effects of octanol on canine subendocardial Purkinje-to-ventricular transmission

1985 ◽  
Vol 249 (6) ◽  
pp. H1228-H1231 ◽  
Author(s):  
R. W. Joyner ◽  
E. D. Overholt
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Current Flow ◽  
Conduction Delay ◽  
Papillary Muscles ◽  
Maximal Rate ◽  
Gap Junctional ◽  
Junctional Resistance ◽  
P Cells

The effects of 0.2 mM octanol on action potential propagation were investigated using in vitro preparations of canine papillary muscles. In these preparations an action potential initiated in the superficial Purkinje (P) layer propagates across specific Purkinje-ventricular junction (PVJ) sites into the underlying ventricular (V) layer. The conduction delay at PVJ sites increased from 4.85 +/- 1.55 to 8.85 +/- 3.34 (mean +/- SD) ms (n = 10, P less than 0.005), an 82% increase. However, propagation within the V syncytium was much less affected, with a decrease of conduction velocity by only 10% and a decrease in the maximal rate of rise of the action potential of 23%. The results indicate that octanol, which has previously been shown to increase gap junctional resistance, has a preferential effect on PVJ sites, as predicted by the hypothesis that there is a restricted pathway for intracellular current flow from P cells to V cells at these sites.

Rhythmic hyperpolarizations and depolarization of sympathetic ganglion cells induced by caffeine

1976 ◽  
Vol 39 (3) ◽  
pp. 547-563 ◽  
Author(s):  
K. Kuba ◽  
S. Nishi
Keyword(s):  
Action Potential ◽  
Sympathetic Ganglion ◽  
External Medium ◽  
Ganglion Cells ◽  
Membrane Resistance ◽  
Free Medium ◽  
Dibutyryl Cyclic Amp ◽  
High K ◽  
Hyperpolarizing Response ◽  
K Permeability

Superfusion of the isolated sympathetic ganglion of the bullfrog with a caffeine-containing (1-6 mM) solution caused in many cells an initial slow hyperpolarization which was followed by a subliminal depolarization interruped by rhythmic hyperpolarizations. A hyperpolarization, similar to one of the rhythmic hyperpolarizations, could be triggered by an action potential in the presence of caffeine. The action potential itself was not markedly affected by caffeine except for its afterhyperpolarization which was prolonged. All these caffeine-induced hyperpolarizations were associated with a marked reduction of the membrane resistance, their amplitude was increased in a K+-free solution and decreased in a high-K+ solution, and their polarity was reversed at the same level at which the afterhyperpolarization was also inverted. This reversal level was not altered by omission of Na+ or C1- from the external medium. These hyperpolarizations were reversibly abolished by depletion of external Ca2+ or replacement of external Ca2+ by Mg2+. Excess of external Ca2+ caused a shortening of the interval between rhythmic hyperpolarizations. Furthermore, iontophoretic injection of EDTA into the cytoplasm markedly depressed the initial caffeine hyperpolarizatin and abolished both the rhythmic and evoked caffeine hyperpolarizations. The caffeine-induced depolarization was not affected by omission of external Cl-. It was decreased in a Na+-free medium, but completely eliminated by omission of both Na+ and Ca2+ from the external medium. Tetrodotoxin did not impair the production of the initial and the rhythmic hyperpolarizations. A strong depolarizing pulse could evoke a typical hyperpolarizing response in the presence of this compound. Dibutyryl cyclic AMP, d-tubocurarine, atropine, and phenoxybenzamine were without effect on the caffeine-induced hyperpolarizations and depolarization. It was concluded that each caffeine-induced hyperpolarization is the result of an increased K+ permeability, which is probably caused by a rise in the internal Ca2+ concentration. It was also concluded that the caffeine-induced depolarization is due to an increased membrane permeability to Ca2+ and Na+.

Intracellular recording from pectoral fin motoneurons of the stingray Dasyatis sabina, an elasmobranch fish

1984 ◽  
Vol 51 (4) ◽  
pp. 666-679 ◽  
Author(s):  
B. J. Williams ◽  
M. H. Droge ◽  
R. B. Leonard
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Initial Segment ◽  
Recurrent Events ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
Pectoral Fin ◽  
Dasyatis Sabina ◽  
Axonal Conduction ◽  
Input Conductance

Intracellular recordings were made from antidromically identified pectoral fin motoneurons in unanesthetized, decerebrate stingrays (Dasyatis sabina). These recordings had the three all-or-none components seen in other vertebrate motoneuron recordings. About 25% of the impalements had resting membrane potentials that were greater than -80 mV, which is larger than those of motoneurons from other vertebrate species. A novel depolarizing afterpotential (DAP) is associated with the isolated action potential occurring at the first node of Ranvier of the axon (M-spike). Occlusion experiments exclude recurrent events as the source of this potential. A capacitive source for the DAP is postulated. Using morphological and passive electrical data on motoneurons from previous studies, calculations of the passive decay of the nodal spike indicate that the membrane resistance of the initial segment is low and nearly equal to that of nodal membrane. The soma-dendritic (SD) spike is followed by a prominent, humped delayed depolarization (DD). The DD is temporally associated with the onset of the action potential produced by the initial segment (IS spike). Sources of the long-lasting period of repolarization recorded with the IS spike, which may underlie the DD, are postulated. The afterhyperpolarization (AHP) of stingray motoneurons tends to be shorter and smaller in amplitude than that of other vertebrate motoneurons. A negligible conductance change was often found during the period following an SD spike. No significant correlation was found between AHP duration and axonal conduction velocity. The input conductance of stingray motoneurons ranged between 1.5 X 10(-7) and 13.3 X 10(-7) S. The relationship between input conductance and axonal conduction velocity was determined from 42 motoneurons. These data were fitted by a power function with an exponent of 1.7, indicating that, in terms of membrane conductance properties, large stingray motoneurons are simply scaled-up versions of the small motoneurons.

scholarly journals Membrane Potentials of the Lobster Giant Axon Obtained by Use of the Sucrose-Gap Technique

1962 ◽  
Vol 45 (6) ◽  
pp. 1195-1216 ◽  
Author(s):  
Fred J. Julian ◽  
John W. Moore ◽  
David E. Goldman
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Sea Water ◽  
Sucrose Solution ◽  
Chloride Concentration ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Gap Technique ◽  
Sucrose Gap

A method similar to the sucrose-gap technique introduced be Stäpfli is described for measuring membrane potential and current in singly lobster giant axons (diameter about 100 micra). The isotonic sucrose solution used to perfuse the gaps raises the external leakage resistance so that the recorded potential is only about 5 per cent less than the actual membrane potential. However, the resting potential of an axon in the sucrose-gap arrangement is increased 20 to 60 mv over that recorded by a conventional micropipette electrode when the entire axon is bathed in sea water. A complete explanation for this effect has not been discovered. The relation between resting potential and external potassium and sodium ion concentrations shows that potassium carries most of the current in a depolarized axon in the sucrose-gap arrangement, but that near the resting potential other ions make significant contributions. Lowering the external chloride concentration decreases the resting potential. Varying the concentration of the sucrose solution has little effect. A study of the impedance changes associated with the action potential shows that the membrane resistance decreases to a minimum at the peak of the spike and returns to near its initial value before repolarization is complete (a normal lobster giant axon action potential does not have an undershoot). Action potentials recorded simultaneously by the sucrose-gap technique and by micropipette electrodes are practically superposable.

scholarly journals Electrical Characteristics and Activation Potential of Bufo Eggs

1959 ◽  
Vol 43 (1) ◽  
pp. 139-157 ◽  
Author(s):  
Takashi Maéno
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Membrane Resistance ◽  
Chloride Ions ◽  
Potassium Ions ◽  
Ionic Mechanism ◽  
Electrical Characteristics ◽  
Activation Potential ◽  
Specific Permeability ◽  
Toad Bufo

Electrical characteristics and their changes during activation were studied with the microelectrodes on the oocytes and eggs of the toad, Bufo vulgaris formosus Boulenger. In young oocytes, the membrane characteristics had some similarities to those of nerve and muscle, except for a relatively large resistance of 25 KΩcm.2 and an absence of the action potential in the former. After maturation, however, the membrane characteristics became entirely different from those of oocytes and other excitable tissues. In the mature eggs the membrane resistance was measured to be as high as 200 KΩcm.2, and no specific permeability of the membrane to potassium ions was observable. A slow monophasic change in the membrane potential was recorded in every activation produced by mechanical stimulation, and termed "activation potential." In fresh water, its amplitude was as large as 80 to 90 mv. with an overshoot of about 50 mv. The activation potential might be comparable to the action potential of nerve and muscle, but was fundamentally different in ionic mechanism from the latter, since the former was caused by a marked increase in permeability to chloride ions.

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