Development of Na(+)- and K(+)-currents in the cochlear ganglion of the chick embryo.
The development of Na(+)- and K(+)-currents in the primary afferent neurons of the cochlear ganglion was studied using the patch-clamp technique. Cells were dissociated between days 6 and 17 of development and membrane currents recorded within the following 24 h. Outward currents were the first to appear between days 6 and 7 of embryonic development and their magnitude increased throughout development from 200 pA on day 7 to 900 pA on days 14-16. Threshold for activation decreased by 20 mV between days 8 and 14. Outward currents were absent when Cs+ replaced K+ in the pipette and were partially blocked by external tetraethylammonium. Outward currents contained at least three components: (i) a non-inactivating outward current, similar to the delayed-rectifier, predominating in mature neurons; (ii) a slowly inactivating current (tau about 200 ms), most evident in early and intermediate stages (days 7-10); and (iii) a rapidly inactivating outward current (tau about 20 ms) similar to the A-current (IA) described in other neurons, which was distinctly expressed in mature neurons. Sodium currents were identified as fast transient inward currents, sensitive to tetrodotoxin and extracellular Na(+)-removal. They appeared later than K(+)-currents and increased in size from about 100 pA between days 9-11 to 600 pA by days 13-16. The development of membrane currents in cochlear ganglion neurons corresponded to defined stages of the innervation pattern of the chick cochlea [Whitehead and Morest (1985) Neuroscience 14, 255-276]. These currents could be functionally related to the establishment of synaptic connections between transducing cells and primary afferent neurons.
Valverde
M A
MA
Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid, Spain.
Sheppard
D N
DN
Represa
J
J
Giraldez
F
F
D000818:Animals; D002642:Chick Embryo; D003051:Cochlea / Q000166:cytology / Q000378:metabolism*; D004594:Electrophysiology; D005724:Ganglia / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D007150:Immunohistochemistry; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D015221:Potassium Channels; D015222:Sodium Channels; D013779:Tetrodotoxin