Inactivation of delayed rectifier K+ current in semicircular canal hair cells

Some properties of the inactivation process of delayed rectifier K+ current (Ik) were investigated in vestibular hair cells of the central region of frog crista ampullaris. These cells were chosen since they exhibited a very large Ik. Experiments were performed on thin slices of sensory epithelium using the whole-cell variant of the patch-clamp technique. Ik showed clear time-dependent inactivation over a period of some seconds, but the current did not completely inactivate even after 30 s depolarizing pulses. Another interesting finding was that inactivation could be well fitted by the sum of two exponentials: at 20 mV depolarization the fast time constant was 291.3 ms and the slow time constant was 2662.3 ms. In addition, an analysis of the steady-state inactivation process of Ik revealed that the inactivation curve was incomplete showing a non-inactivating current at potentials more positive than -50 mV. These results suggested that Ik in hair cells of frog crista ampullaris is composed of more than one component: by at least one inactivating and one non-inactivating component. The possible role of these components in hair cell excitability is discussed.