Spider toxins: A new group of potassium channel modulators

Spider toxins that target potassium channels constitute a new class of pharmacological tools that can be used to probe the structure and function of these channels at the molecular level. The limited studies performed to date indicate that these peptide toxins may facilitate the analysis of K⁺ channels that have proved insensitive to peptide inhibitors isolated from other animal sources. Thus far, two classes of K⁺ channel-selective spider toxins have been isolated, sequenced, and pharmacologically characterised - the hanatoxins (HaTx) from Grammastola spatulata and heteropodatoxins (HpTx) from Heteropoda venatoria. The hanatoxins block Kv2.1 and Kv4.2 voltage-gated K⁺ channels. In Kv2.1 K⁺ channels this occurs as a consequence of a depolarising shift in the voltage dependence of activation and not by occlusion of the channel pore. These toxins show minimal sequence homology with other peptide inhibitors of K⁺ channels, but they do share some homology with other ion channel toxins from spiders, particularly with regard to the spacing between cysteine residues. We have recently isolated three K⁺ channel antagonists from the venom of the Australian funnel-web spider Hadronyche versuta; at least two of these toxins are likely to constitute a new class of spider toxins active on K⁺ channels as they are approximately twice as large as HaTx and HpTx.