title: Ontogenic development of the TTX-sensitive and TTX-insensitive Na+ channels in neurons of the rat dorsal root ganglia.
abstract: Developmental changes in the sensitivity of neurons to tetrodotoxin (TTX) were studied in relation to the cell size in rat dorsal root ganglia (DRG). Na+ currents were recorded from neurons of various stages of development. Two types of Na+ channels were identified on the basis of their sensitivity to TTX. One type was insensitive to a very high concentration (0.1 mM) of TTX, while the other type was blocked by a low concentration (1 nM) of TTX. These two types of Na+ channels were observed throughout the developmental stages examined from day 17 of gestation and adulthood. Thus, both types of Na+ channels are already established at the early stage of neuronal development and appear to be retained throughout the life-span of the DRG neuron. The concentration-response relationships for the block of TTX-sensitive Na+ current by TTX did not appreciably change during development. Although two types of Na+ channels had strikingly different kinetic properties, the kinetic properties of each channel type were basically similar throughout development. The TTX-sensitive Na+ channels were mainly concentrated in cells with large cell diameters throughout developmental stages examined. These large cells appear to correspond to the 'large-light' cells. On the contrary, the TTX-insensitive Na+ channels were found in smaller diameter cells which may correspond to the 'small-dark' cells. Thus, it is concluded that there are heterogeneous categories of neurons which have Na+ channels with different physiological and pharmacological properties. Since Na+ channels play a pivotal role in the action potential generation, these heterogeneity of DRG neurons appear to be instrumental in integrating the sensory signals.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Fukuoka, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Ogata
authors.forename: H
authors.initials: H
authors.lastname: Tatebayashi
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism*; D005314:Embryonic and Fetal Development; D005727:Ganglia, Spinal / Q000166:cytology / Q000196:embryology*; D009474:Neurons / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009994:Osmolar Concentration; D051381:Rats; D012964:Sodium / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology*
chemical_list: D015222:Sodium Channels; D013779:Tetrodotoxin; D012964:Sodium; D002118:Calcium