Fig. 9.

Kv3-type channels are the main voltage-gated K⁺ channels contributing to the fast repolarizations and afterhyperpolarizations during action potential trains in BCs.A, B, Train of action potentials evoked in a BC (whole-cell, current-clamp recording) by a current pulse (1 sec, 160 pA), in the absence (A) and presence (B) of 0.2 mm 4-AP. Membrane potential before the pulse was −70 mV (holding current, −40 pA). One hundred micromolar Cd²⁺ was used in the external solution in both conditions. C, K⁺ current in a BC patch during a high frequency train. The experimentally recorded action potential pattern was applied as voltage-clamp command (inset). The resulting current is shown in the absence (top trace) and presence (bottom trace) of 0.2 mm 4-AP, with 0.3 μm TTX added to the bath solution. Average of 10 individual sweeps, leak and capacitive currents were subtracted by a P over −4 procedure. Holding potential, −70 mV. Different BCs inA, B, and C.D, Summary graph of deactivation and activation time constants of the Kv3-like K⁺ current component in BCs plotted against voltage. The voltage trajectories of BC action potentials are shown on the right.