Potently and reversibly inhibits the insect voltage-gated Shaker (Sh) potassium channel (isoform alpha (B)), the mammalian voltage-gated potassium channels Kv1.2/KCNA2 (IC(50)=0.44 nM), and the calcium-activated potassium channel KCa2.3/KCNN3 (Kd=330 nM) (PubMed:9001397, PubMed:10931199, PubMed:11527975). Its effect on Kv1.3/KCNA3 is controversial, since this channel is voltage-independently inhibited in PubMed:9464266, but is not affected in PubMed:10931199. Furthermore, this toxin competes with apamin (a small conductance calcium-activated potassium channel inhibitor) for binding to rat brain synaptosomes. Expressed by the venom gland. Has the structural arrangement of an alpha-helix connected to a beta-sheet by disulfide bonds (CSalpha/beta). The alpha-helical domain may play a key role in the recognition of SK channels. The beta-sheet structure may be involved in bioactivity on Kv channels. LD(50) is 10 ug/kg by intraperitoneal injection into mice. Pi1 analog that is synthesized with a phosphorylation at Tyr-33 (P-Pi1) suffers a 200-fold decrease in LD(50), a 200-fold decrease of potency in competition assay with apamin, and a 58-fold decrease in inhibiting Kv1.2/KCNA2 channels. Does not or very weakly inhibits KCa2.2/KCNN2 (Kd> 1 uM) and Kv1.1/KCNA1 (no effect observed at 5 uM). Belongs to the short scorpion toxin superfamily. Potassium channel inhibitor family. Alpha-KTx 06 subfamily.