Outward potassium currents activated by depolarization in rat globus pallidus

Voltage-dependent potassium currents play a key role in shaping the firing pattern of central neurons. Their pharmacological and physiological identification is rather important in the structures which are involved 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 potassium conductances which have been indicated to condition the firing behavior 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 calcium-independent outward potassium currents are activated by depolarization in GPe neurons acutely isolated from the adult rat. From depolarized holding potentials (-50/-45 mV), a slowly-activating, sustained current is evoked; it manifests very little inactivation and it is available at rather depolarized potentials (-30 mV/-20 mV). This current is relatively resistant to 4-aminopyridine (4-AP) but it is blocked by tetraethilammonium ions (TEA) and consequently it resembles delayed rectifier current (Ik). From negative holding potentials (-80/-100 mV), on the other hand, A-like conductances are activated. Together with a fast-inactivating transient current, another component is observed in a significant proportion of recordings (45%). This current shows half-inactivation voltage around -90 mV, peculiar sensitivity to micromolar doses of 4-AP and a slow rate of recovery from inactivation. The presence and the modulation of these A-like currents may be a very critical aspect in the membrane physiology of pallidal neurons.