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

1962 ◽  
Vol 46 (2) ◽  
pp. 257-266 ◽  
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).

scholarly journals Temperature Characteristics of Excitation in Space-Clamped Squid Axons

1966 ◽  
Vol 49 (5) ◽  
pp. 1007-1018 ◽  
Author(s):  
Rita Guttman ◽  
Keyword(s):  
Giant Axon ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Effect Of Temperature ◽  
Axon Membrane ◽  
Temperature Characteristics ◽  
Gap Technique ◽  
Threshold Strength ◽  
Sucrose Gap ◽  
Good Agreement

Temperature characteristics of excitability in the squid giant axon were measured for the space-clamped axon with the double sucrose gap technique. Threshold strength-duration curves were obtained for square wave current pulses from 10 µsec to 10 msec and at temperatures from 5°C to 35°C. The threshold change of potential, at which an action potential separated from a subthreshold response, averaged 17 mv at 20°C with a Q10 of 1.15. The average threshold current density at rheobase was 12 µa/cm2 at 20°C with a Q10 of 2.35 compared to 2.3 obtained previously. At short times the threshold charge was 1.5·10-8 coul/cm2. This was relatively independent of temperature and occasionally showed a minimum in the temperature range. At intermediate times and all temperatures the threshold currents were less than for both the single time constant model and the two factor excitation process as developed by Hill. FitzHugh has made computer investigations of the effect of temperature on the excitation of the squid axon membrane as represented by the Hodgkin-Huxley equations. These are in general in good agreement with our experimental results.

scholarly journals Liquid Junction and Membrane Potentials of the Squid Giant Axon

1960 ◽  
Vol 43 (5) ◽  
pp. 971-980 ◽  
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.

scholarly journals Structural complexes in the squid giant axon membrane sensitive to ionic concentrations and cardiac glycosides

1976 ◽  
Vol 69 (1) ◽  
pp. 19-28 ◽  
Author(s):  
GM Villegas ◽  
J Villegas
Keyword(s):  
Cardiac Glycosides ◽  
Sea Water ◽  
Giant Axon ◽  
Structural Features ◽  
Nerve Fibers ◽  
Axon Membrane ◽  
Ionic Concentrations ◽  
Low Concentrations ◽  
High Calcium ◽  
Active Ion Transport

Giant nerve fibers of squid Sepioteuthis sepiodea were incubated for 10 min in artificial sea water (ASW) under control conditions, in the absence of various ions, and in the presence of cardiac glycosides. The nerve fibers were fixed in OsO(4) and embedded in Epon, and structural complexes along the axolemma were studied. These complexes consist of a portion of axolemma exhibiting a three-layered substructure, an undercoating of a dense material (approximately 0.1μm in length and approximately 70-170 A in thickness), and a narrowing to disappearance of the axon-Schwann cell interspace. In the controls, the incidence of complexes per 1,000μm of axon perimeter was about 137. This number decreased to 10-25 percent when magnesium was not present in the incubating media, whatever the calcium concentration (88, 44, or 0 mM). In the presence of magnesium, the number and structural features of the complexes were preserved, though the number decreased to 65 percent when high calcium was simultaneously present. The complexes were also modified and decreased to 26-32 percent by incubating the nerves in solutions having low concentrations of sodium and potassium. The adding of 10(-5) M ouabain or strophanthoside to normal ASW incubating solution decreased them to 20-40 percent. Due to their sensitivity to changes in external ionic concentrations and to the presence of cardiac glycosides, the complexes are proposed to represent the structural correlate of specialized sites for active ion transport, although other factors may be involved.

scholarly journals LONGITUDINAL IMPEDANCE OF THE SQUID GIANT AXON

1941 ◽  
Vol 24 (6) ◽  
pp. 771-788 ◽  
Author(s):  
Kenneth S. Cole ◽  
Richard F. Baker
Keyword(s):  
Sea Water ◽  
Low Frequency ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Dielectric Characteristics ◽  
Impedance Characteristics ◽  
Longitudinal Impedance ◽  
Electrode Length ◽  
Interpolar Distance ◽  
Inductive Reactance

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.

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 Non-Linear Current-Potential Relations in an Axon Membrane

1961 ◽  
Vol 44 (6) ◽  
pp. 1055-1057 ◽  
Author(s):  
Kenneth S. Cole
Keyword(s):  
Membrane Potential ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
External Current ◽  
Current Electrode ◽  
Axon Membrane ◽  
Linear Current ◽  
One Step ◽  
Original Derivation ◽  
Current Potential

The membrane current density, Im, in the squid giant axon has been calculated from the measured external current applied to the axon, Io, by the equation See PDF for Equation where Vm is the membrane potential under the current electrode and r1 and r2 are the external and internal longitudinal resistances. The original derivation of this equation included in one step an assumption of a linear relation between Im and Vm. It is shown that the same equation can be obtained without this restricting assumption.

scholarly journals KINETICS OF ION MOVEMENT IN THE SQUID GIANT AXON

1955 ◽  
Vol 39 (2) ◽  
pp. 279-300 ◽  
Author(s):  
Abraham M. Shanes ◽  
Morris D. Berman
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Cortical Layer ◽  
Central Segment ◽  
Exponential Decline ◽  
Rate Of Emergence ◽  
The Individual ◽  
Two Stages ◽  
Ion Species ◽  
Kinetics Of

The loss of Na22, K42, and Cl36 from single giant axons of the squid, Loligo pealii, following exposure to an artificial sea water containing these radioisotopes, occurs in two stages, an initial rapid one followed by an exponential decline. The time constants of the latter stage for the 3 ion species are, respectively, 290, 200, and 175 minutes. The outflux of sodium is depressed while that of potassium is accelerated in the absence of oxygen; the emergence of potassium is slowed by cocaine, while that of sodium is unaffected. One cm. ends of the axons take up about twice as much radiosodium as the central segment; this difference in activity is largely preserved during exposure to inactive solution. Such marked differences are not observed with radiopotassium. From the experimental data estimates are given of the influxes and outfluxes of the individual ions. The kinetics of outflux suggests a cortical layer of measureable thickness which contains the ions in different proportions from those in the medium and which governs the rate of emergence of these ions from the axon as though it contained very few but large (relative to ion dimensions) pores.

scholarly journals RECTIFICATION AND INDUCTANCE IN THE SQUID GIANT AXON

1941 ◽  
Vol 25 (1) ◽  
pp. 29-51 ◽  
Author(s):  
Kenneth S. Cole
Keyword(s):  
Membrane Potential ◽  
Electrical Properties ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Constant Current ◽  
Ion Permeability ◽  
Squid Axon ◽  
Axon Membrane ◽  
Piezoelectric Structure ◽  
In Series

Previous measurements have shown that the electrical properties of the squid axon membrane are approximately equivalent to those of a circuit containing a capacity shunted by an inductance and a rectifier in series. Selective ion permeability of a membrane separating two electrolytes may be expected to give rise to the rectification. A quasi-crystalline piezoelectric structure of the membrane is a plausible explanation of the inductance. Some approximate calculations of behavior of an axon with these membrane characteristics have been made. Fair agreement is obtained with the observed constant current subthreshold potential and impedance during the foot of the action potential. In a simple case a formal analogy is found between the calculated membrane potential and the excitability defined by the two factor formulations of excitation. Several excitation phenomena may then be explained semi-quantitatively by further assuming the excitability proportional to the membrane potential. Some previous measurements and subthreshold potential and excitability observations are not consistent with the circuit considered and indicate that this circuit is only approximately equivalent to the membrane.

Sign in / Sign up

Export Citation Format

Share Document