INACTIVATION OF DELAYED RECTIFIER K-CELLS( CURRENT IN SEMICIRCULAR CANAL HAIR)

SOME properties of the inactivation process of delayed rectifier K+ cu rrent (I-k) were investigated in vestibular hair cells of the central region of frog crista ampullaris. These cells were chosen since they e xhibited a very large I-k. Experiments were performed on thin slices o f sensory epithelium using the whole-cell variant of the patch-clamp t echnique. I-k showed clear time-dependent inactivation over a period o f some seconds, but the current did not completely inactivate even aft er 30 s depolarizing pulses. Another interesting finding was that inac tivation 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 i nactivation process of I-k revealed that the inactivation curve was in complete showing a non-inactivating current at potentials more positiv e than -50 mV. These results suggested that I-k 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.