Selectively and irreversibly binds (K(d)=2.9 pM) and blocks hKv1.3/KCNA3 potassium channels of human T-lymphocytes. Weakly blocks hKCa3.1/KCNN4, mKv1.1/KCNA1, and hKv1.2/KCNA2 channels. In vivo, high doses (200 ug) produce no symptoms of intoxication when injected into mice. Expressed by the venom gland. Has the CSalpha/beta fold, which comprises one or two short alpha helices connected to anti-parallel beta-sheets stabilized by three or four disulfide bonds. Has the structural arrangement of an alpha-helix connected to antiparallel beta-sheets by disulfide bonds (CS-alpha/beta). Does not block hKv1.4/KCNA4, hKv1.5/KCNA5, rKv2.1/KCNB1, hBK, hERG, Nav1.5/SCN5A channels when assayed at a concentration of 10 nM. Belongs to the short scorpion toxin superfamily. Potassium channel inhibitor family. Alpha-KTx 23 subfamily.