OUTWARD POTASSIUM CURRENTS ACTIVATED BY DEPOLARIZATION IN RAT GLOBUS-PALLIDUS

Voltage-dependent potassium currents play a key role in shaping the fi ring pattern of central neurons. Their pharmacological and physiologic al identification is rather important in the structures which are invo lved in the filtering of input/output messages. In this regard, globus pallidus external segment (GPe) is indicated as a crucial station in the well-known indirect pathway of the basal ganglia. Among the potass ium conductances which have been indicated to condition the firing beh avior and the neuronal integrative properties in many central neurons, we analysed the depolarization-activated ones by means of patch-clamp recordings in the whole-cell configuration. Two main families of calc ium-independent outward potassium currents are activated by depolariza tion in GPe neurons acutely isolated from the adult rat. From depolari zed holding potentials (-50/-45 mV), a slowly-activating, sustained cu rrent is evoked; it manifests very little inactivation and it is avail able at rather depolarized potentials (-30 mV/-20 mV). This current is relatively resistant to 4-aminopyridine (4-AP) but it is blocked by t etraethilammonium ions (TEA) and consequently it resembles delayed rec tifier current (Ik) From negative holding potentials (-80/-100 mV), on the other hand, A-like conductances are activated. Together with a fa st-inactivating transient current, another component is observed in a significant proportion of recordings (45%). This current shows half-in activation voltage around -90 mV, peculiar sensitivity to micromolar d oses of 4-AP and a slow rate of recovery from inactivation. The presen ce and the modulation of these A-like currents may be a very critical aspect in the membrane physiology of pallidal neurons. (C) 1995 Wiley- Liss, Inc.