scholarly journals Endocytotic elimination and domain-selective tethering constitute a potential mechanism of protein segregation at the axonal initial segment

2004 ◽  
Vol 166 (4) ◽  
pp. 571-578 ◽  
Author(s):  
Marie-Pierre Fache ◽  
Anissa Moussif ◽  
Fanny Fernandes ◽  
Pierre Giraud ◽  
Juan José Garrido ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Hippocampal Neurons ◽  
Initial Segment ◽  
Distal Part ◽  
Potential Mechanism ◽  
Reporter Protein ◽  
Linker Sequence ◽  
Axonal Initial Segment ◽  
Cellular Polarization

The axonal initial segment is a unique subdomain of the neuron that maintains cellular polarization and contributes to electrogenesis. To obtain new insights into the mechanisms that determine protein segregation in this subdomain, we analyzed the trafficking of a reporter protein containing the cytoplasmic II–III linker sequence involved in sodium channel targeting and clustering (Garrido, J.J., P. Giraud, E. Carlier, F. Fernandes, A. Moussif, M.P. Fache, D. Debanne, and B. Dargent. 2003. Science. 300:2091–2094). Here, we show that this reporter protein is preferentially inserted in the somatodendritic domain and is trapped at the axonal initial segment by tethering to the cytoskeleton, before its insertion in the axonal tips. The nontethered population in dendrites, soma, and the distal part of axons is subsequently eliminated by endocytosis. We provide evidence for the involvement of two independent determinants in the II–III linker of sodium channels. These findings indicate that endocytotic elimination and domain-selective tethering constitute a potential mechanism of protein segregation at the axonal initial segment of hippocampal neurons.

Sodium channels and compartmentalization at the axonal initial segment

2006 ◽  
Vol 99 (2-3) ◽  
pp. 1
Author(s):  
Anissa Moussif ◽  
Marie-Pierre Fache ◽  
Fanny Fernandes ◽  
Pierre Giraud ◽  
Juan José Garrido ◽  
...  
Keyword(s):  
Sodium Channels ◽  
Initial Segment ◽  
Axonal Initial Segment

scholarly journals Protein kinase CK2 contributes to the organization of sodium channels in axonal membranes by regulating their interactions with ankyrin G

2008 ◽  
Vol 183 (6) ◽  
pp. 1101-1114 ◽  
Author(s):  
Aline Bréchet ◽  
Marie-Pierre Fache ◽  
Anna Brachet ◽  
Géraldine Ferracci ◽  
Agnés Baude ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Protein Kinase Ck2 ◽  
Binding Motif ◽  
Nodes Of Ranvier ◽  
Ankyrin G ◽  
Axonal Initial Segment ◽  
Kinase Ck2

In neurons, generation and propagation of action potentials requires the precise accumulation of sodium channels at the axonal initial segment (AIS) and in the nodes of Ranvier through ankyrin G scaffolding. We found that the ankyrin-binding motif of Nav1.2 that determines channel concentration at the AIS depends on a glutamate residue (E1111), but also on several serine residues (S1112, S1124, and S1126). We showed that phosphorylation of these residues by protein kinase CK2 (CK2) regulates Nav channel interaction with ankyrins. Furthermore, we observed that CK2 is highly enriched at the AIS and the nodes of Ranvier in vivo. An ion channel chimera containing the Nav1.2 ankyrin-binding motif perturbed endogenous sodium channel accumulation at the AIS, whereas phosphorylation-deficient chimeras did not. Finally, inhibition of CK2 activity reduced sodium channel accumulation at the AIS of neurons. In conclusion, CK2 contributes to sodium channel organization by regulating their interaction with ankyrin G.

Late Sodium Channel Openings Underlying Epileptiform Activity Are Preferentially Diminished by the Anticonvulsant Phenytoin

1997 ◽  
Vol 77 (6) ◽  
pp. 3021-3034 ◽  
Author(s):  
Michael M. Segal ◽  
Andrea F. Douglas
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Hippocampal Neurons ◽  
Sodium Current ◽  
Epileptiform Activity ◽  
Normal Function ◽  
Anticonvulsant Effect ◽  
Persistent Sodium Current ◽  
Pharmacological Mechanism ◽  
Voltage Dependent

Segal, Michael M. and Andrea F. Douglas. Late sodium channel openings underlying epileptiform activity are preferentially diminished by the anticonvulsant phenytoin. J. Neurophysiol. 77: 3021–3034, 1997. Late openings of sodium channels were observed in outside-out patch recordings from hippocampal neurons in culture. In previous studies of such neurons, a persistent sodium current appeared to underlie the ictal epileptiform activity. All the channel currents were blocked by tetrodotoxin. In addition to the transient openings of sodium channels making up the peak sodium current, there were two types of late channel openings: brief late and burst openings. These late channel openings occurred throughout voltage pulses that lasted 750 ms, producing a persistent sodium current. At −30 mV, this current was 0.4% of the peak current. The late channel openings occurred throughout the physiological range of trans-membrane voltages. The anticonvulsant phenytoin reduced the late channel openings more than the peak currents. The effect on the persistent current was greatest at more depolarized voltages, whereas the effect on peak currents was not substantially voltage dependent. In the presence of 60 μM phenytoin, peak sodium currents at −30 mV were 40–41% of control, as calculated using different methods of analysis. Late currents were 22–24% of control. Phenytoin primarily decreased the number of channel openings, with less effect on the duration of channel openings and no effect on open channel current. This set of findings is consistent with models in which phenytoin binds to the inactivated state of the channel. The preferential effect of phenytoin on the persistent sodium current suggests that an important pharmacological mechanism for a sodium channel anticonvulsant is to reduce late openings of sodium channels, rather than reducing all sodium channel openings. We hypothesize that pharmacological interventions that are most selective in reducing late openings of sodium channels, while leaving early channel openings relatively intact, will be those that produce an anticonvulsant effect while interfering minimally with normal function.

scholarly journals Drosophila Voltage-Gated Sodium Channels Are Only Expressed in Active Neurons and Are Localized to Distal Axonal Initial Segment-like Domains

2020 ◽  
Vol 40 (42) ◽  
pp. 7999-8024 ◽  
Author(s):  
Thomas A. Ravenscroft ◽  
Jasper Janssens ◽  
Pei-Tseng Lee ◽  
Burak Tepe ◽  
Paul C. Marcogliese ◽  
...  
Keyword(s):  
Sodium Channels ◽  
Initial Segment ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Axonal Initial Segment

scholarly journals Ankyrin G restricts ion channel diffusion at the axonal initial segment before the establishment of the diffusion barrier

2010 ◽  
Vol 191 (2) ◽  
pp. 383-395 ◽  
Author(s):  
Anna Brachet ◽  
Christophe Leterrier ◽  
Marie Irondelle ◽  
Marie-Pierre Fache ◽  
Victor Racine ◽  
...  
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Diffusion Barrier ◽  
Hippocampal Neurons ◽  
Initial Segment ◽  
Specific Binding ◽  
Single Particle Tracking ◽  
Binding Motif ◽  
Ankyrin G ◽  
Axonal Initial Segment

In mammalian neurons, the precise accumulation of sodium channels at the axonal initial segment (AIS) ensures action potential initiation. This accumulation precedes the immobilization of membrane proteins and lipids by a diffusion barrier at the AIS. Using single-particle tracking, we measured the mobility of a chimeric ion channel bearing the ankyrin-binding motif of the Nav1.2 sodium channel. We found that ankyrin G (ankG) limits membrane diffusion of ion channels when coexpressed in neuroblastoma cells. Site-directed mutants with decreased affinity for ankG exhibit increased diffusion speeds. In immature hippocampal neurons, we demonstrated that ion channel immobilization by ankG is regulated by protein kinase CK2 and occurs as soon as ankG accumulates at the AIS of elongating axons. Once the diffusion barrier is formed, ankG is still required to stabilize ion channels. In conclusion, our findings indicate that specific binding to ankG constitutes the initial step for Nav channel immobilization at the AIS membrane and precedes the establishment of the diffusion barrier.

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