FIGURE 8.

Interaction with the inactivated state: steady-state parameters. (A) The graph shows relative current amplitudes upon channel activations in the presence of different concentrations of TIC10, after a prolonged inactivation. (B) Experimental scheme, illustrating the double pulse protocol. Starting from a holding potential of −140 mV channels were inactivated for 20 s at a potential of −20 mV. After a short recovery at holding potential, the control pulse was executed. Between the control and test run (second part), ample time (10 s) for full recovery was provided. In the second part, the protocol was repeated in either control or test solution. For evaluation, test current amplitudes were related to their controls. Data analysis was restricted to data sets where control and test-pulse amplitude in mere control solution did not deviate by more than 3%. Overall, half-maximal inhibition (IC₅₀), representing the affinity for the inactivated state (K_i) was calculated to be 2.0 ± 0.5 µM.