LONGITUDINAL IMPEDANCE OF THE SQUID GIANT AXON

Longitudinal alternating current impedance measurements have been made on the squid giant axon over the frequency range from 30 cycles per second to 200 kc. per second. Large sea water electrodes were used and the inter-electrode length was immersed in oil. The impedance at high frequency was approximately as predicted theoretically on the basis of the poorly conducting dielectric characteristics of the membrane previously determined. For the large majority of the axons, the impedance reached a maximum at a low frequency and the reactance then vanished at a frequency between 150 and 300 cycles per second. Below this frequency, the reactance was inductive, reaching a maximum and then approaching zero as the frequency was decreased. The inductive reactance is a property of the axon and requires that it contain an inductive structure. The variation of the impedance with interpolar distance indicates that the inductance is in the membrane. The impedance characteristics of the membrane as calculated from the measured longitudinal impedance of the axon may be expressed by an equivalent membrane circuit containing inductance, capacity, and resistance. For a square centimeter of membrane the capacity of 1 µf with dielectric loss is shunted by the series combination of a resistance of 400 ohms and an inductance of one-fifth henry.

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MEMBRANE AND PROTOPLASM RESISTANCE IN THE SQUID GIANT AXON

The Journal of General Physiology ◽

10.1085/jgp.22.5.671 ◽

1939 ◽

Vol 22 (5) ◽

pp. 671-687 ◽

Cited By ~ 93

Author(s):

Kenneth S. Cole ◽

Alan L. Hodgkin

Keyword(s):

Sea Water ◽

Characteristic Length ◽

Giant Axon ◽

Squid Giant Axon ◽

Separation Curve ◽

Electrode Separation ◽

Electrode Length ◽

Longitudinal Resistance ◽

Small Electrode ◽

Connective Tissue Sheath

The direct current longitudinal resistance of the squid giant axon was measured as a function of the electrode separation. Large sea water electrodes were used and the inter-electrode length was immersed in oil. The slope of the resistance vs. separation curve is large for a small electrode separation, but becomes smaller and finally constant as the separation is increased. An analysis of the resistance vs. length curves gives the following results. The nerve membrane has a resistance of about 1000 ohm cm.2 The protoplasm has a specific resistance of about 1.4 times that of sea water. The resistance of the connective tissue sheath outside the fiber corresponds to a layer of sea water about 20µ in thickness. The characteristic length for the axon is about 2.3 mm. in oil and 6.0 mm. in sea water.

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Effect of Temperature on the Potential and Current Thresholds of Axon Membrane

The Journal of General Physiology ◽

10.1085/jgp.46.2.257 ◽

1962 ◽

Vol 46 (2) ◽

pp. 257-266 ◽

Cited By ~ 9

Author(s):

Rita Guttman ◽

Keyword(s):

Sea Water ◽

Sucrose Solution ◽

Giant Axon ◽

Threshold Current ◽

Squid Giant Axon ◽

Effect Of Temperature ◽

Threshold Potential ◽

Axon Membrane ◽

Central Segment ◽

The Mean

The effect of temperature on the potential and current thresholds of the squid giant axon membrane was measured with gross external electrodes. A central segment of the axon, 0.8 mm long and in sea water, was isolated by flowing low conductance, isoosmotic sucrose solution on each side; both ends were depolarized in isoosmotic KCl. Measured biphasic square wave currents at five cycles per second were applied between one end of the nerve and the membrane of the central segment. The membrane potential was recorded between the central sea water and the other depolarized end. The recorded potentials are developed only across the membrane impedance. Threshold current values ranged from 3.2 µa at 267deg;C to 1 µa at 7.5°C. Threshold potential values ranged from 50 mv at 26°C to 6 mv at 7.5°C. The mean Q10 of threshold current was 2.3 (SD = 0.2), while the Q10 for threshold potentials was 2.0 (SD = 0.1).

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Action of External Divalent Ion Reduction on Sodium Movement in the Squid Giant Axon

The Journal of General Physiology ◽

10.1085/jgp.45.1.93 ◽

1961 ◽

Vol 45 (1) ◽

pp. 93-103 ◽

Cited By ~ 25

Author(s):

William J. Adelman ◽

John W. Moore

Keyword(s):

Sea Water ◽

Giant Axon ◽

Sodium Concentration ◽

Squid Giant Axon ◽

Ion Concentration ◽

Resting Potential ◽

Slow Increase ◽

Sodium Permeability ◽

Sodium Accumulation ◽

Sodium Flux

Voltage clamp measurements of the sodium potential have been made on the resting squid giant axon to study the effect of variations in external divalent ion concentration upon net sodium flux. From these measurements the intracellular sodium concentration and the net sodium inflow were calculated using the Nernst relation and constant activity coefficients. While an axon bathed in artificial sea water shows a slow increase in internal sodium concentration, the rate of sodium accumulation is increased about two times by reducing external calcium and magnesium concentrations to 0.1 times their normal values. The mean inward net sodium flux increases from a mean control value of 97 pmole/cm2 sec. to 186 pmole/cm2 sec. in low divalent solution. Associated with these effects of external divalent ion reduction are a marked decrease in action potential amplitude, little or no change in resting potential, and a shift along the voltage axis of the curve relating peak sodium conductance to membrane potential similar to that obtained by Frankenhaeuser and Hodgkin (1957). These results implicate divalent ions in long term (minutes to hours) sodium permeability.

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LOW LEVEL IMPEDANCE CHANGES FOLLOWING THE SPIKE IN THE SQUID GIANT AXON BEFORE AND AFTER TREATMENT WITH "VERATRINE" ALKALOIDS

The Journal of General Physiology ◽

10.1085/jgp.37.1.39 ◽

1953 ◽

Vol 37 (1) ◽

pp. 39-51 ◽

Cited By ~ 21

Author(s):

Abraham M. Shanes ◽

Harry Grundfest ◽

Walter Freygang

Keyword(s):

Sea Water ◽

Giant Axon ◽

Squid Giant Axon ◽

Satisfactory Explanation ◽

Chloride Permeability ◽

Potential Oscillations ◽

Temporal Course ◽

Before And After ◽

Conductance Changes ◽

Conductance Increase

The increase in conductance, which accompanies the spike in the presence of sea water, is followed by a decrease to below the resting level, here designated as the "initial after-impedance," which lasts 3 msec. and is 3 per cent as great as the increase. Treatment with cevadine usually obliterates the latter but leaves the former essentially unaltered. In addition, the alkaloid gives rise to periodic conductance increases followed by a prolonged, exponentially decaying elevated conductance (the "negativity after-impedance") which correspond closely to potential oscillations and to the negative after-potential. These are also only a few per cent of the major conductance change. Veratridine causes a conductance increase which lasts longer and which also conforms closely with earlier after-potential results. Preliminary calculations indicate that the negativity after-impedance and the negative after-potential may be due to the subsidence of an elevated chloride permeability. However, no satisfactory explanation is available for the initial after-impedance or for the temporal course of the conductance changes associated with oscillations in membrane potential.

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Liquid Junction and Membrane Potentials of the Squid Giant Axon

The Journal of General Physiology ◽

10.1085/jgp.43.5.971 ◽

1960 ◽

Vol 43 (5) ◽

pp. 971-980 ◽

Cited By ~ 25

Author(s):

Kenneth S. Cole ◽

John W. Moore

Keyword(s):

Membrane Potential ◽

Sea Water ◽

Specific Resistance ◽

Cumulative Effect ◽

Giant Axon ◽

Squid Giant Axon ◽

Liquid Junction ◽

Axon Membrane ◽

Best Value ◽

Liquid Junction Potentials

The potential differences across the squid giant axon membrane, as measured with a series of microcapillary electrodes filled with concentrations of KCl from 0.03 to 3.0 M or sea water, are consistent with a constant membrane potential and the liquid junction potentials calculated by the Henderson equation. The best value for the mobility of an organic univalent ion, such as isethionate, leads to a probably low, but not impossible, axoplasm specific resistance of 1.2 times sea water and to a liquid junction correction of 4 mv. for microelectrodes filled with 3 M KCl. The errors caused by the assumptions of proportional mixing, unity activity coefficients, and a negligible internal fixed charge cannot be estimated but the results suggest that the cumulative effect of them may not be serious.

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EFFECTS OF EXTERNAL IONS ON MEMBRANE POTENTIALS OF A LOBSTER GIANT AXON

The Journal of General Physiology ◽

10.1085/jgp.41.3.529 ◽

1958 ◽

Vol 41 (3) ◽

pp. 529-542 ◽

Cited By ~ 54

Author(s):

John C. Dalton

Keyword(s):

Action Potential ◽

Sea Water ◽

Giant Axon ◽

Membrane Potentials ◽

Squid Giant Axon ◽

Resting Potential ◽

Magnesium Concentration ◽

Constant Field ◽

Order Of Magnitude ◽

External Calcium

The effects of varying external concentrations of normally occurring cations on membrane potentials in the lobster giant axon have been studied and compared with data presently available from the squid giant axon. A decrease in the external concentration of sodium ions causes a reversible reduction in the amplitude of the action potential and its rate of rise. No effect on the resting potential was detected. The changes are of the same order of magnitude, but greater than would be predicted for an ideal sodium electrode. Increase in external potassium causes a decrease in resting potential, and a decrease in potassium causes an increase in potential. The data so obtained are similar to those which have been reported for the squid giant axon, and cannot be exactly fitted to the Goldman constant field equation. Lowering external calcium below 25 mM causes a reduction in resting and action potentials, and the occasional occurrence of repetitive activity. The decrease in action potential is not solely attributable to a decrease in resting potential. Increase of external calcium from 25 to 50 mM causes no change in transmembrane potentials. Variations of external magnesium concentration between zero and 50 mM had no measurable effect on membrane potentials. These studies on membrane potentials do not indicate a clear choice between the use of sea water and Cole's perfusion solution as the better external medium for studies on lobster nerve.

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Neurofilaments and Paired Helical Filaments

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100120357 ◽

1985 ◽

Vol 43 ◽

pp. 740-743

Author(s):

J. Metuzals

Keyword(s):

Animal Model ◽

Posttranslational Modifications ◽

Posttranslational Modification ◽

Giant Axon ◽

Paired Helical Filaments ◽

Squid Giant Axon ◽

In Vitro Experiments ◽

Thin Sections ◽

Structural Relationships

It has been demonstrated that the neurofibrillary tangles in biopsies of Alzheimer patients, composed of typical paired helical filaments (PHF), consist also of typical neurofilaments (NF) and 15nm wide filaments. Close structural relationships, and even continuity between NF and PHF, have been observed. In this paper, such relationships are investigated from the standpoint that the PHF are formed through posttranslational modifications of NF. To investigate the validity of the posttranslational modification hypothesis of PHF formation, we have identified in thin sections from frontal lobe biopsies of Alzheimer patients all existing conformations of NF and PHF and ordered these conformations in a hypothetical sequence. However, only experiments with animal model preparations will prove or disprove the validity of the interpretations of static structural observations made on patients. For this purpose, the results of in vitro experiments with the squid giant axon preparations are compared with those obtained from human patients. This approach is essential in discovering etiological factors of Alzheimer's disease and its early diagnosis.

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