Voltage-activated sodium conductances in cultured normal and trisomy 16 dorsal root ganglion neurons from the fetal mouse.
Current and voltage clamp recordings were made with a patch-clamp technique from large, light, dorsal root ganglia (DRG) neurons in tissue culture, derived from trisomy 16 and normal fetal mice. In a Na gradient of [52 mM]o/[28 mM]i, the action potential was accelerated, depolarization and repolarization were faster and the total Na conductance was higher in trisomic neurons. A tetrodotoxin (TTX)-sensitive, fast Na current was demonstrated, about 0.9 nA in trisomic and 0.3 nA in control neurons. The calculated mean specific membrane conductances were 0.74 mS/cm2 and 0.28 mS/cm2, respectively. A TTX-insensitive, slow Na conductance, 3-4 times the fast Na conductance and sensitive to Cd, also was demonstrated, with a 2-fold greater current density and conductance in trisomic as compared with control neurons, of 2.22 +/- 0.54 mS/cm2 and 1.26 +/- 0.09 mS/cm2, respectively. The voltage-dependence and kinetics of the TTX-insensitive, slow, Na current were similar in the two neuronal groups. The results indicate that depolarization during the action potential, in fetal mouse DRG neurons in culture, is mediated by this slow TTX-insensitive Na current. Further, acceleration of depolarization in trisomy 16 neurons is caused by a 2-fold increase in the density of the slow Na current.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D002885:Chromosomes, Human, Pair 16; D003035:Cobalt / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D012964:Sodium / Q000378:metabolism / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014314:Trisomy
D007473:Ion Channels; D003035:Cobalt; D013779:Tetrodotoxin; D012964:Sodium