Development of a fast transient potassium current in chick cochlear ganglion neurons.
Neurons of the cochlear ganglion are endowed with a set of voltage-gated ion channels that enable them to encode and transmit sound information from the cochlear receptors to the brain. The temporal expression pattern of the K+ currents in chick cochlear ganglion neurons during embryonic development was analyzed using whole-cell voltage clamp techniques. In acutely isolated neurons, slowly activating delayed rectifier K+ currents appear at embryonic day 7 (E7) and increase in amplitude during development. A fast activating, fast inactivating K+ current of the A type is first expressed at E10, increasing in amplitude thereafter. To investigate the possible role of neurotrophins in the induction of these K+ channels, neurons were grown in culture in the presence or absence of brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3). Neurons isolated at E8 and grown in culture for 1 day exhibit a high expression of A-current, together with the outgrowth of neurites. A-currents are not seen in acutely dissociated neurons from age-matched embryos (E9) which lack neurites, cut off by the isolation procedure. This suggests a preferential neuritic location of the channels carrying the A-current. However, the level of expression of the K+ currents was independent of BDNF or NT-3 application. Similarly, neurons isolated at E10 and grown in culture for up to 4 days maintain the amplitude of the K+ currents independently of the presence of the neurotrophins. These results indicate that BDNF and NT-3 may not directly regulate the expression of K+ channels in chick cochlear ganglion neurons. The notable expression of the fast inactivating A-current suggests that it plays a significant role in the modulation of synaptic efficacy and the encoding of auditory stimuli.
García-Díaz
J F
JF
Department of Physiology, Boston University School of Medicine, MA 02118, USA. fgarcia@bu.edu
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D002642:Chick Embryo; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D013136:Spiral Ganglion / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D009435:Synaptic Transmission; D019789:Tetraethylammonium / Q000494:pharmacology
D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011188:Potassium