Intracellular Ca2+is required for the effect of synaptotagmin I on Kv1.4 currents. One day after transfection, HEK293T cells were incubated for 20–26 h with BAPTA-AM (10 μM in 0.1%DMSO) or 0.1%DMSO alone as a control. Currents were measured at +30 mV 2 days after the injection. (A)-(B) Current traces of Kv1.4 and Kv1.4/synaptotagmin I after the cells were incubated with 0.1% DMSO (A) or 10 μM BAPTA-AM (B). (C) Inactivation time constants (τinact) under the two different conditions. Data are expressed as mean ± SD. After the cells were incubated with 0.1% DMSO, the τinact of Kv1.4 current expressed with and without synaptotagmin I were 38.1 ± 2.3 ms (n = 9) and 68.8 ± 2.6 ms (n = 9), respectively (p < 0.05). When the cells were incubated with BAPTA-AM, the τinact values of the channel under the two different conditions were not significantly different (p > 0.05). (D)-(E) Effects of synaptotagmin I on the inactivation of Kv1.4 channels at different concentrations of Ca2+(D) and their corresponding τinact values (E).