Transient outward currents in cochlear ganglion neurons of the chick embryo.
Cochlear ganglion neurons were isolated from chick embryos and membrane currents recorded using the patch-clamp technique. Depolarizing voltage steps elicited transient outward currents whose inactivation was best fitted by a double-exponential function with time constants < 30 ms and > 100 ms. The fast inactivating transient outward current (Ito,f) had a threshold for activation of -61 +/- 5.5 mV; steady-state inactivation was voltage-dependent between -90 and -60 mV, with half-inactivation near -75 mV. The slowly inactivating outward current (Ito,s) showed an activation threshold of 34 +/- 4 mV. Half-inactivation was at -67 +/- 3 mV. Ito,f was blocked by 4-aminopyridine which did not affect Ito,s. The effect was concentration- and voltage-dependent. Tetraethylammonium had no effect on either fast or slow transient currents but reduced the amplitude of the non-inactivating outward current in a dose-dependent manner. Ito,f was strongly inhibited by removing Ca2+ from the extracellular bathing solution. Cobalt ions inhibited Ito,f in a dose-dependent manner between 2 and 20 mM. The inhibitory effect of Co2+ was voltage-dependent, displaying a bell-shaped inhibition curve as a function of membrane voltage, maximal inhibition occurring between -20 and 0 mV. Ca2+ removal did not affect Ito,s and partially reduced the amplitude of the steady-state current. These results provide kinetic and pharmacological evidence for the presence of two distinct transient outward currents in cochlear neurons. These currents may play a role in the first synaptic relay of sound transmission.
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D002642:Chick Embryo; D003035:Cobalt / Q000494:pharmacology; D003051:Cochlea / Q000294:innervation* / Q000502:physiology; D004594:Electrophysiology; D005724:Ganglia / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D003035:Cobalt; D015761:4-Aminopyridine; D002118:Calcium