Differential targeting and functional specialization of sodium channels in cultured cerebellar granule cells.
The ion channel dynamics that underlie the complex firing patterns of cerebellar granule (CG) cells are still largely unknown. Here, we have characterized the subcellular localization and functional properties of Na+ channels that regulate the excitability of CG cells in culture. As evidenced by RT-PCR and immunocytochemical analysis, morphologically differentiated CG cells expressed Nav1.2 and Nav1.6, though both subunits appeared to be differentially regulated. Nav1.2 was localized at most axon initial segments (AIS) of CG cells from 8 days in vitro DIV 8 to DIV 15. At DIV 8, Nav1.6 was found uniformly throughout somata, dendrites and axons with occasional clustering in a subset of AIS. Accumulation of Nav1.6 at most AIS was evident by DIV 13-14, suggesting it is developmentally regulated at AIS. The specific contribution of these differentially distributed Na+ channels has been assessed using a combination of methods that allowed discrimination between functionally compartmentalized Na+ currents. In agreement with immunolocalization, we found that fast activating-fully inactivating Na+ currents predominate at the AIS membrane and in the somatic plasma membrane.
Osorio
Nancy
N
Laboratoire de Neurophysiologie Cellulaire, CNRS UMR 6150, IFR Jean Roche, Faculté de Médecine, Boulevard Pierre Dramard, 13916, Marseille Cedex 20, France.
Alcaraz
Gisèle
G
Padilla
Françoise
F
Couraud
François
F
Delmas
Patrick
P
Crest
Marcel
M
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism*; D003712:Dendrites / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020128:Inhibitory Concentration 50; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000187:drug effects; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C568253:Scn2A protein, rat; D015222:Sodium Channels; D013779:Tetrodotoxin; D012964:Sodium