Effects of synaptotagmin I on Kv1.4 kinetics expressed in HEK293T cells. (A) Representative traces of Kv1.4 currents expressed alone. (B) Representative traces of Kv1.4 currents coexpressed with synaptotagmin I. Currents were elicited by depolarizing steps from -80 to 70 mV in 10 mV increments every 45 s from a holding potential of -80 mV. (C) Currents recorded upon depolarization to +30 mV. (D) Inactivation time constants (τinact) of the indicated channel obtained at +30 mV. Data are expressed as mean ± SD. The τinact of Kv1.4 current expressed alone was 31.1 ms ± 2.3 ms (n = 13), compared with 64.8 ± 4.5 ms (n = 9) for Kv1.4 current coexpressed with synaptotagmin I (p < 0.05). (E) Activation curves of Kv1.4 and Kv1.4/synaptotagmin I. Current amplitudes recorded from the channels were normalized to the maximal response at +30 mV and plotted as a function of the membrane potential.