Current and voltage responses recorded from IHCs of Cx30(−/−) mice. A, B, Potassium currents recorded from P18 IHCs of wild-type (A) and littermate Cx30(−/−) (B) mice using depolarizing voltage steps in 10 mV nominal increments from the holding potential of −84 mV to the various test potentials shown by some of the traces. The adult-type currents (I_K,f and I_K,n) were only present in IHCs from wild-type mice (A). IHCs from Cx30(−/−) mice retained the currents characteristic of immature cells (I_K,s and I_K1). The presence of the rapidly activating I_K,f in control IHCs is evident when comparing the activation time course of the total outward currents shown in the insets on an expanded time scale. C–E, Voltage responses elicited by applying hyperpolarizing and depolarizing current injections to control (C) and Cx30(−/−) adult IHCs (D, E) from their respective membrane potentials. In some IHCs, depolarizing current injections caused slow APs at the onset of responses. Recordings were performed at room temperature.