Received for publication April 24, 2006.
Revised June 28, 2006.
Accepted for publication June 29, 2006.

Interaction of riluzole with the closed-inactivated state of Kv4.3 channels

Abstract

The effect of riluzole on Kv4.3 was examined using the whole-cell patch-clamp technique. Riluzole inhibited the peak amplitude of Kv4.3 in a reversible, concentration-dependent manner with an IC₅₀ of 115.6 µM. Under control conditions, a good fit for the inactivation of Kv4.3 currents to a double exponential function, with the time constants of the fast component (_f) and the slow component (_s) was obtained. _f was not altered by riluzole at concentrations up to 100 µM but ]_s became slower with increasing riluzole concentration, resulting in the cross-over of the currents. The inhibition increased steeply with increasing channel activation at more positive potentials. In the full activation voltage range positive to +30 mV, however, no voltage-dependent inhibition was found. Riluzole shifted the voltage dependence of the steady-state inactivation of Kv4.3 in the hyperpolarizing direction in a concentration-dependent manner. However, the slope factor was not affected by riluzole. The K_i for riluzole for interacting with the inactivated state of Kv4.3 was estimated from the concentration-dependent shift in the steady-state inactivation curve and was determined to be 1.2 µM. Under control conditions, closed-state inactivation was fitted to a single exponential function. Riluzole caused a substantial acceleration in the closed-state inactivation. In the presence of riluzole, the recovery from inactivation was slower than under control conditions. Riluzole induced a significant use-dependent inhibition of Kv4.3. These results suggest that riluzole inhibits Kv4.3 by binding to the closed-inactivated state of the channels and that the unbinding of riluzole occurs from the closed state during depolarization.

Key words: A-type currents, Kv4.3, anticonvulsant, inactivation, neuroprotection, riluzole