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 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 Grayanotoxin, veratrine, and tetrodotoxin-sensitive sodium pathways in the Schwann cell membrane of squid nerve fibers.

1976 ◽  
Vol 67 (3) ◽  
pp. 369-380 ◽  
Author(s):  
J Villegas ◽  
C Sevcik ◽  
F V Barnola ◽  
R Villegas
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Schwann Cell ◽  
Nerve Fiber ◽  
Schwann Cells ◽  
Giant Axon ◽  
Nerve Fibers ◽  
Resting Membrane Potential ◽  
External Application ◽  
Axon Membrane

The actions of grayanotoxin I, veratrine, and tetrodotoxin on the membrane potential of the Schwann cell were studied in the giant nerve fiber of the squid Sepioteuthis sepioidea. Schwann cells of intact nerve fibers and Schwann cells attached to axons cut lengthwise over several millimeters were utilized. The axon membrane potential in the intact nerve fibers was also monitored. The effects of grayanotoxin I and veratrine on the membrane potential of the Schwann cell were found to be similar to those they produce on the resting membrane potential of the giant axon. Thus, grayanotoxin I (1-30 muM) and veratrine (5-50 mug-jl-1), externally applied to the intact nerve fiber or to axon-free nerve fiber sheaths, produce a Schwann cell depolarization which can be reversed by decreasing the external sodium concentration or by external application of tetrodotoxin. The magnitude of these membrane potential changes is related to the concentrations of the drugs in the external medium. These results indicate the existence of sodium pathways in the electrically unexcitable Schwann cell membrane of S. sepioidea, which can be opened up by grayanotoxin I and veratrine, and afterwards are blocked by tetrodotoxin. The sodium pathways of the Schwann cell membrane appear to be different from those of the axolemma which show a voltage-dependent conductance.

scholarly journals FINE STRUCTURAL ALTERATIONS ASSOCIATED WITH VENOM ACTION ON SQUID GIANT NERVE FIBERS

1968 ◽  
Vol 36 (2) ◽  
pp. 341-353 ◽  
Author(s):  
Rainer Martin ◽  
Philip Rosenberg
Keyword(s):  
Giant Axon ◽  
Nerve Fibers ◽  
Squid Giant Axon ◽  
Cetyltrimethylammonium Chloride ◽  
Axonal Membrane ◽  
Structural Alterations ◽  
Low Concentrations ◽  
Rattlesnake Venom ◽  
Direct Lytic Factor ◽  
Small Nerve

(1) Block of conduction and marked increase in permeability of the squid giant axon, when surrounded by adhering small nerve fibers, is caused by the venoms of cottonmouth, ringhals, and cobra snakes and by phospholipase A (PhA). This phenomenon is associated with a marked breakdown of the substructure of the Schwann sheath into masses of cytoplasmic globules. Low concentrations of these agents which render the axons sensitive to curare cause less marked changes in the structure of the sheath. (2) Rattlesnake venom, the direct lytic factor obtained from ringhals venom, and hyaluronidase caused few observable changes in structure, correlating with the inability of these agents to increase permeability. (3) Cottonmouth venom did not alter the structure of giant axons freed of all adhering small nerve fibers. This is in agreement with previous evidence that the venom effects are due to an action of lysophosphatides liberated as a result of PhA action. Cetyltrimethylammonium chloride, a cationic detergent, produces effects that resemble those of venom and PhA. (4) The results provide evidence that PhA is the component of the venoms that is responsible for their effects. It also appears that the Schwann cell and possibly the axonal membrane are the major permeability barriers in the squid giant axon.

scholarly journals Axonal Adaptations to Osmotic and Ionic Stress in an Invertebrate Osmoconformer (Mercierella Enigmatica Fauvel): I. Ultrastructural and Electrophysiological Observations on Axonal Accessibility

1978 ◽  
Vol 76 (1) ◽  
pp. 191-204
Author(s):  
H. LE B. SKAER ◽  
J. E. TREHERNE ◽  
J. A. BENSON
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Initial Exposure ◽  
Axon Membrane ◽  
Ionic Lanthanum ◽  
Ionic Stress ◽  
Hyposmotic Stress ◽  
Intercellular Clefts ◽  
Junctional Complexes ◽  
Theoretical Considerations

The giant axons in Mercierella are overlaid by narrow glial processes which provide an incomplete covering of the axonal surface. Where more complete covering occurs the intercellular clefts are not sealed by tight junctional complexes. Ionic lanthanum penetrates to the surfaces of axons from sea-water-adapted animals (in normal saline and during initial exposure to hyposmotic saline) and, also, to the surface of hyposmotically adapted axons. A relatively free intercellular access to the axon surfaces is also indicated by the rapid electrical responses of sea-water-adapted axons to hyposmotic dilution and of hyposmotically adapted axons to sodium-deficient saline. The giant axon possesses an unusual ultrastructural specialization: hemidesmosome-like structures (associated with the axon membrane) which are connected to a network of neuronlaments within the axon. Theoretical considerations suggest that these structures could enable the axons to withstand appreciable excesses in intracellular hydrostatic pressure resulting from osmotic imbalance during hyposmotic stress. Note: The Editor reports, with deep regret, the apparent passing of Mercierella enigmatica which it is now proposed becomes Ficopotamus enigmaticus (Fauvel) (ten Hove & Weerdenburg, 1978, Biol. Bull. 154, 96–120).

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 The Action of Certain Polyvalent Cations on the Voltage-Clamped Lobster Axon

1968 ◽  
Vol 51 (3) ◽  
pp. 279-291 ◽  
Author(s):  
M. P. Blaustein ◽  
D. E. Goldman
Keyword(s):  
Metal Ions ◽  
Potassium Conductance ◽  
Binding Constants ◽  
Membrane Conductance ◽  
Giant Axon ◽  
Transition Metal Ions ◽  
Cation Binding ◽  
Axon Membrane ◽  
High Calcium ◽  
Excitation Processes

Calcium appears to be an essential participant in axon excitation processes. Many other polyvalent metal ions have calcium-like actions on axons. We have used the voltage-clamped lobster giant axon to test the effect of several of these cations on the position of the peak initial (sodium) and steady-state (potassium) conductance vs. voltage curves on the voltage axis as well as on the rate parameters for excitation processes. Among the alkaline earth metals, Mg+2 is a very poor substitute for Ca+2, while Ba+2 behaves like "high calcium" when substituted for Ca+2 on a mole-for-mole basis. The transition metal ions, Ni+2, Co+2, and Cd+2 also act like high calcium when substituted mole-for-mole. Among the trivalent ions, La+3 is a very effective Ca+2 replacement. Al+3 and Fe+3 are extremely active and seem to have some similar effects. Al+3 is effective at concentrations as low as 10-5 M. The data suggest that many of these ions may interact with the same cation-binding sites on the axon membrane, and that the relative effects on the membrane conductance and rate parameters depend on the relative binding constants of the ions. The total amount of Na+ transferred during a large depolarizing transient is nearly independent of the kind or amount of polyvalent ion applied.

scholarly journals TRANSVERSE ELECTRIC IMPEDANCE OF THE SQUID GIANT AXON

1938 ◽  
Vol 21 (6) ◽  
pp. 757-765 ◽  
Author(s):  
Howard J. Curtis ◽  
Kenneth S. Cole
Keyword(s):  
Current Flow ◽  
Transverse Electric ◽  
Sea Water ◽  
Specific Resistance ◽  
Giant Axon ◽  
Simple Analysis ◽  
Axon Membrane ◽  
Polarization Impedance ◽  
Direct Current Resistance ◽  
Current Resistance

The impedance of the excised giant axon from hindmost stellar nerve of Loligo pealii has been measured over the frequency range from 1 to 2500 kilocycles per second. The measurements have been made with the current flow perpendicular to the axis of the axon to permit a relatively simple analysis of the data. It has been found that the axon membrane has a polarization impedance with an average phase angle of 76° and an average capacity of 1.1µf./cm2 at 1 kilocycle. The direct current resistance of the membrane could not be measured, but was greater than 3 ohm cm.2 and the average internal specific resistance was four times that of sea water. There was no detectable change in the membrane impedance when the axon lost excitability, but some time later it decreased to zero.

scholarly journals Current-Voltage Relations in the Lobster Giant Axon Membrane Under Voltage Clamp Conditions

1962 ◽  
Vol 45 (6) ◽  
pp. 1217-1238 ◽  
Author(s):  
Fred J. Julian ◽  
John W. Moore ◽  
David E. Goldman
Keyword(s):  
Steady State ◽  
Voltage Clamp ◽  
Sea Water ◽  
Outward Current ◽  
Giant Axon ◽  
Squid Axon ◽  
Initial Current ◽  
Axon Membrane ◽  
Current Voltage ◽  
Steady State Current

The sucrose-gap method introduced by Stämpfli provides a means for the application of a voltage clamp to the lobster giant axon, which responds to a variety of different experimental procedures in ways quite similar to those reported for the squid axon and frog node. This is particularly true for the behavior of the peak initial current. However, the steady state current shows some differences. It has a variable slope conductance less than that of the peak initial current. The magnitude of the steady state slope conductance is related to the length of the repolarization phase of the action potential, which does not have an undershoot in the lobster. The steady state outward current is maintained for as long as 100 msec.; this is in contrast to a decline of about 50 per cent in the squid axon. Lowering the external calcium concentration produces shifts in the current-voltage relations qualitatively similar to those obtained from the squid axon. On the basis of the data available, there is no reason to doubt that the Hodgkin and Huxley analysis for the squid giant axon in sea water can be applied to the lobster giant axon.

scholarly journals Resting and Action Potentials of the Squid Giant Axon in Vivo

1960 ◽  
Vol 43 (5) ◽  
pp. 961-970 ◽  
Author(s):  
John W. Moore ◽  
Kenneth S. Cole
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Blood Oxygenation ◽  
Resting Potential ◽  
Liquid Junction ◽  
Axon Membrane ◽  
Nernst Potential ◽  
Initial Action ◽  
Calculated Liquid

Blood oxygenation and circulation were maintained in Loligo pealii for several hours by a strong flow of sea water over both gills on the open, flat mantle. Potentials were measured with a 3 M KCl-filled glass microelectrode penetrating the giant axon membrane. An hour or more after the mantle was opened, the potentials were similar to those observed in excised axons and in preparations without circulation; spike height 100 mv.; undershoot 12 mv., decaying at 6 v./sec.; resting potential 63 mv. However, the earliest (20 minute) resting potentials were up to 70 mv. and 73 mv. Occasional initial action potential measurements (40 to 50 minute) showed a decay of the undershoot that was less than one-tenth the rate observed later. This suggests that in even better preparations there would be no decay, thereby increasing the resting potential and spike height by 12 mv. With the calculated liquid junction potential of 4 mv. the absolute resting potential in the "normal" axon in vivo is estimated to be about 77 mv., which is close to the Nernst potential for the potassium ratio between squid blood and axoplasm. The differences between such a normal axon and the usual isolated axon can be accounted for by a negligible leakage conductance in the normal axon.

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