The study investigates the fast inactivation mechanism of the potassium channel Kv1.3. Specifically, it examines the effect of a mutant form of the channel, A413V, on the inactivation process. The study uses electrophysiological techniques such as whole-cell patch-clamp recording to measure the current flowing through the channel in response to changes in the concentration of external potassium ions, as well as the application of the drug TEA to block the channel. The results suggest that the A413V mutation is more sensitive to TEA, with a slowed down inactivation process. Additionally, the study shows that the drug TEA has a stronger blocking effect on the A413V mutant channel compared to the wild-type channel, indicating a change in the conformation of the channel. The findings provide insights into the mechanism of fast inactivation in potassium channels and may have implications for the development of drugs that target Kv1.3 channels in diseases such as multiple sclerosis and autoimmune disorders.