OSK-1 is a potent potassium channel blocker belonging to the α-KTx3 toxins. It exhibits IC50 values of 0.6 nM, 5.4 nM, and 0.014 nM for Kv1.1, Kv1.2, and Kv1.3 channels, respectively. Additionally, OSK-1 acts as a moderate blocker of the calcium-activated KCa3.1 channel, with an IC50 of 225 nM. Consequently, OSK-1 finds application as an immunosuppressive drug.