Effect of synaptotagmin I on the kinetics of Kv1.4[K532Y]. (A) Representative traces of Kv1.4[K532Y] currents expressed alone. (B) Representative traces of Kv1.4[K532Y] 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 channels obtained at +30 mV. Data are expressed as mean ± SD. The inactivation of Kv1.4 [K532Y] was significantly (p < 0.05) affected by the coexpressed synaptotagmin I. The τinact of Kv1.4 [K532Y] was 36.6 ± 1.3 ms (n = 9). When coexpressed with synaptotamin I, its τinact was 64.5 ± 1.6 ms (n = 12). (E) Activation curves of Kv1.4[K532Y] and Kv1.4[K532Y]/synaptotagmin I. Current amplitudes recorded were normalized to the maximal response at +30 mV and plotted as a function of the membrane potential.