Chloride channel ligand. Potently and reversibly inhibits CFTR chloride channels when the channels are in the interburst closed state. May also interact with chloride channels (probably ClC-3/CLCN3) and MMP2 at the surface of glioma cells. This complex may be then internalized via caveolae, thus inhibiting the chloride channels necessary for cell shrinkage and tumor propagation. Expressed by the venom gland. Does not inhibit ClC-1/CLCN1, ClC-2/CLCN2 or ClC-3/CLCN3 voltage-gated chloride channels, GABA(C)/GABRR receptors, Shaker Kv1.1/KCNA1 potassium channels, or the multidrug resistance proteins ABCC1 (MRP1), ABCC2 (MRP2) and ABCC3 (MRP3). Belongs to the short scorpion toxin superfamily. Chloride channel inhibitor family.