Oocytes were injected with mRNA encoding Kv1.1 alone, Kv1.5 alone, or both Kv1.1 and Kv1.5 cRNA. A, voltage dependence of activation of Kv1.1 alone (•), Kv1.5 alone (▪) and co-injected Kv1.1 plus Kv1.5 (♦) currents. Normalized Kv1.1 tail currents were fitted with a Boltzmann function. The V1/2 and k values were, respectively, -30.3 mV and 7.4 mV for Kv1.1 (n = 6), -13.1 mV and 8.0 mV for Kv1.5 (n = 6), -23.9 mV and 7.1 mV for co-injected Kv1.1 plus Kv1.5 (n = 6). B, the steady-state response of homo- and heterotetramers of Kv1.1 and Kv1.5 to 1 nm DTX-K was measured as the late current during a 400 ms voltage step from a holding potential of -80 mV to 0 mV. DTX-K inhibited currents encoded by Kv1.1 alone (80 ± 6 %, n = 5), and co-injected Kv1.1 plus Kv1.5 (68 ± 6 %, n = 5), but not Kv1.5 alone (3 ± 1 %, n = 4). C, illustrative currents in the absence (○) and presence (⋄) of 1 nm DTX-K.