The Inactivation of Sodium Channels in the Node of Ranvier and Its Chemical Modification

Ion Channels ◽  
1990 ◽  
pp. 123-168 ◽  
Author(s):  
Werner Ulbricht
Keyword(s):  
Chemical Modification ◽  
Sodium Channels ◽  
Node Of Ranvier

scholarly journals Permeability of the sodium channel in Myxicola to organic cations.

1976 ◽  
Vol 68 (5) ◽  
pp. 551-562 ◽  
Author(s):  
L Binstock
Keyword(s):  
Sodium Channels ◽  
Organic Cation ◽  
Reversal Potential ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Giant Axon ◽  
Organic Cations ◽  
Relative Permeabilities ◽  
Potential Control ◽  
Goldman Equation

The relative permeability of sodium channels to organic cations was determined in the Myxicola giant axon. Ionic currents under potential control were measured in seawater and in sodium-free solutions containing the organic cation. The measured reversal potential and the Goldman equation were used to obtain the relative permeabilities. The permeability sequence was found to be: sodium greater than hydroxylamine greater than hydrazine greater than ammonium greater than guanidine greater than formamidine greater than aminoguanidine greater than methylamine. Measurements were also made on sodium and several of the organic cations at different concentrations. The relative permeabilities of the ions were found to be independent of concentration. Qualitatively, the permeability sequence for the Myxicola giant axon was similar to that of the frog node of Ranvier.

Effects of chemical modification of amino and sulfhydryl groups on the voltage-clamped frog node of Ranvier

1984 ◽  
Vol 400 (4) ◽  
pp. 403-408 ◽  
Author(s):  
Michael Rack ◽  
Shi-ling Hu ◽  
Norbert Rubly ◽  
Christel Waschow
Keyword(s):  
Chemical Modification ◽  
Node Of Ranvier ◽  
Sulfhydryl Groups

The rate of action of tetrodotoxin on sodium conductance in the squid giant axon

1975 ◽  
Vol 270 (908) ◽  
pp. 365-375 ◽  
Keyword(s):  
Schwann Cell ◽  
Sodium Channels ◽  
Binding Sites ◽  
Node Of Ranvier ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Free Diffusion ◽  
Sodium Conductance ◽  
In Series ◽  
Order Of Magnitude

When tetrodotoxin is applied to or washed away from the squid giant axon, the rates at which the sodium conductance is blocked and unblocked are an order of magnitude smaller than those reported for the isolated node of Ranvier. This slowing is to be expected if in squid the tetrodotoxin binding sites act as a saturable sink in series with the barrier to free diffusion imposed by the presence of the Schwann cell. A comparison has been made between the rates observed experimentally and those calculated for a computer model of the system, in order to estimate the apparent density in the membrane of both specific and non-specific tetrodotoxin binding sites. The figure thus obtained for the number of sodium channels in the squid giant axon, several hundred per square micrometre, agrees well with those derived from other lines of argument.

Immuno-ultrastructural localization of sodium channels at nodes of Ranvier and perinodal astrocytes in rat optic nerve

1989 ◽  
Vol 238 (1290) ◽  
pp. 39-51 ◽  
Keyword(s):  
Optic Nerve ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Node Of Ranvier ◽  
Ultrastructural Localization ◽  
Active Role ◽  
Nodes Of Ranvier ◽  
Electron Microscopic ◽  
Axon Membrane ◽  
Intense Immunoreactivity

Immuno-electron microscopic localization of sodium channels at nodes of Ranvier within adult optic nerve was demonstrated with polyclonal antibody 7493. The 7493 antisera, which is directed against purified sodium channels from rat brain, recognizes a 260 kDa protein in immunoblots of the crude glycoprotein fraction from adult rat optic nerve. Intense immunoreactivity with 7493 antisera was observed at nodes of Ranvier. Axon membrane at the node was densely stained, whereas paranodal and internodal axon membrane did not exhibit immunoreactivity. The axoplasm beneath the nodal membrane displayed variable immunostaining. Neither terminal paranodal oligodendroglial loops nor oligodendrocyte plasmalemma were immunoreactive with 7493 antisera. However, perinodal astrocyte processes exhibited intense immunoreactivity with the anti-sodium channel antisera. Optic nerves incubated with pre-immune sera, or with 7493 antisera that had been pre-adsorbed with purified sodium channel protein, displayed no immunoreactivity. These results demonstrate localization of sodium channels at high density at mammalian nodes of Ranvier and in some perinodal astrocyte processes. The latter observation offers support for an active role for perinodal astrocyte processes in the aggregation of sodium channels within the axon membrane at the node of Ranvier.

scholarly journals Axo-Glial Interactions Regulate the Localization of Axonal Paranodal Proteins

1999 ◽  
Vol 147 (6) ◽  
pp. 1145-1152 ◽  
Author(s):  
Jeffrey L. Dupree ◽  
Jean-Antoine Girault ◽  
Brian Popko
Keyword(s):  
Potassium Channels ◽  
Sodium Channels ◽  
Node Of Ranvier ◽  
Molecular Organization ◽  
Protein Distribution ◽  
Nervous Systems ◽  
Peripheral Nervous Systems ◽  
Axonal Protein

Mice incapable of synthesizing the abundant galactolipids of myelin exhibit disrupted paranodal axo-glial interactions in the central and peripheral nervous systems. Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier. Whereas the clustering of the nodal proteins, sodium channels, ankyrinG, and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered. The potassium channels, which are normally concentrated in the paranode/juxtaparanode, were not restricted to this region but were detected throughout the internode in the galactolipid-defi- cient mice. Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions. Collectively, these findings suggest that the myelin galactolipids are essential for the proper formation of axo-glial interactions and demonstrate that a disruption in these interactions results in profound abnormalities in the molecular organization of the paranodal axolemma.

scholarly journals Glial and neuronal isoforms of Neurofascin have distinct roles in the assembly of nodes of Ranvier in the central nervous system

2008 ◽  
Vol 181 (7) ◽  
pp. 1169-1177 ◽  
Author(s):  
Barbara Zonta ◽  
Steven Tait ◽  
Shona Melrose ◽  
Heather Anderson ◽  
Sheila Harroch ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Sodium Channels ◽  
Molecular Mechanisms ◽  
Nerve Impulse ◽  
Node Of Ranvier ◽  
Nodes Of Ranvier ◽  
Additional Function ◽  
The Central Nervous System ◽  
Adhesion Complex

Rapid nerve impulse conduction in myelinated axons requires the concentration of voltage-gated sodium channels at nodes of Ranvier. Myelin-forming oligodendrocytes in the central nervous system (CNS) induce the clustering of sodium channels into nodal complexes flanked by paranodal axoglial junctions. However, the molecular mechanisms for nodal complex assembly in the CNS are unknown. Two isoforms of Neurofascin, neuronal Nfasc186 and glial Nfasc155, are components of the nodal and paranodal complexes, respectively. Neurofascin-null mice have disrupted nodal and paranodal complexes. We show that transgenic Nfasc186 can rescue the nodal complex when expressed in Nfasc−/− mice in the absence of the Nfasc155–Caspr–Contactin adhesion complex. Reconstitution of the axoglial adhesion complex by expressing transgenic Nfasc155 in oligodendrocytes also rescues the nodal complex independently of Nfasc186. Furthermore, the Nfasc155 adhesion complex has an additional function in promoting the migration of myelinating processes along CNS axons. We propose that glial and neuronal Neurofascins have distinct functions in the assembly of the CNS node of Ranvier.

scholarly journals Kinetics of intramembrane charge movement and conductance activation of batrachotoxin-modified sodium channels in frog node of Ranvier.

1985 ◽  
Vol 86 (3) ◽  
pp. 381-394 ◽  
Author(s):  
J M Dubois ◽  
M F Schneider
Keyword(s):  
Pulse Duration ◽  
Sodium Channels ◽  
Time Course ◽  
Sodium Current ◽  
Node Of Ranvier ◽  
Charge Movement ◽  
Exponential Time ◽  
Current Activation ◽  
Time Courses ◽  
Single Exponential

Sodium current and intramembrane gating charge movement (Q) were monitored in voltage-clamped frog node of Ranvier after modification of all sodium channels by batrachotoxin (BTX). Sodium current activation followed a single-exponential time course, provided a delay was interposed between the onset of the step ON depolarization and that of the current change. The delay decreased with increased ON depolarization and, for a constant ON depolarization, increased with prehyperpolarization. ON charge movement followed a single-exponential time course with time constants tau Q,ON slightly larger than tau Na, ON. For pulses between -70 and -50 mV, tau Q,ON/tau Na,ON = 1.14 +/- 0.08. The OFF charge movement and OFF sodium current tails after a depolarizing pulse followed single-exponential time courses, with tau Q, OFF larger than tau Na, OFF. tau Q,OFF/tau Na,OFF increased with OFF voltage from 1 near -100 mV to 2 near -160 mV. At a set OFF potential (-120 mV), both tau Q,OFF and tau Na,OFF increased with ON pulse duration. The delay in INa activation and the effect of ON pulse duration on tau Q,OFF and tau Na,OFF are inconsistent with a simple two-state, single-transition model for the gating of batrachotoxin-modified sodium channels.

Sign in / Sign up

Export Citation Format

Share Document