Depolarization-activated K+ currents of the bushy neurones of the rat cochlear nucleus in a thin brain slice preparation.

Depolarization-activated outward currents of bushy neurones of 6-14-day-old Wistar rats have been investigated in a brain slice preparation. Under current-clamp, the cells produced a single action potential at the beginning of suprathreshold depolarizing current steps. On voltage-clamp depolarizations, the cells produced a mixed outward K+ current that included a component with rapid activation and rapid inactivation, little TEA+ sensitivity, a half-inactivation voltage of -77 +/- 2 mV (T = 25 degrees C; n = 7; Mean +/- S.E.M.) and single-exponential recovery from inactivation (taurecovery= 12 +/- 1 ms at -100 mV; n=3). This transient component was identified as an A-type K+ current. Bushy cells developed a high-threshold TEA-sensitive K+ current that exhibited less prominent inactivation. These characteristics suggested that this current was associated with the activation of delayed rectifier K+ channels. Bushy neurones also possessed a low-threshold outward K+ current that showed partial inactivation and high 4-aminopyridine sensitivity. Part of this current component was blocked by 200 nmol/l dendrotoxin-I. Application of 100 micromol/l 4-aminopyridine changed the firing behaviour of the bushy neurones from the primary-like pattern to a much less rapidly adapting one, suggesting that the low-threshold current might have important roles in maintaining the physiological function of the cells.