Effects of KCNQ channel blockers on K(+) currents in vestibular hair cells

Linopirdine and XE991, selectiveblockers of K⁺ channels belonging to the KCNQ family, wereapplied to hair cells isolated from gerbil vestibular system and tohair cells in slices of pigeon crista. In type II hair cells, bothcompounds inhibited a slowly activating, slowly inactivating componentof the macroscopic current recruited at potentials above 60 mV. Thedissociation constants for linopirdine and XE991 block were <5µM. A similar component of the current was also blocked by 50 µMcapsaicin in gerbil type II hair cells. All three drugs blocked acurrent component that showed steady-state inactivation and abiexponential inactivation with time constants of ~300 ms and 4 s. Linopirdine (10 µM) reduced inward currents through thelow-voltage-activated K⁺ current in type I hair cells, butconcentrations up to 200 µM had little effect on steady-state outwardK⁺ current in these cells. These results suggest that KCNQchannels may be present in amniote vestibular hair cells.