Charybdotoxin and its effects on potassium channels.

Over the last few years, a considerable amount of information has been obtained regarding K+ channels. Different areas of research have contributed to knowledge in this field. Charybdotoxin (ChTX), a 37-amino acid peptide isolated from venom of the scorpion Leiurus quinquestriatus var. hebraeus, represents a remarkable tool for studying K+ channels. With its use, it has been possible to purify the high-conductance Ca(2+)-activated K+ (maxi-K) channel to homogeneity and determine the subunit composition of this channel. This has led to the discovery of an auxiliary beta-subunit that, when coexpressed with the pore-forming subunit, mSlo, alters the biophysical and pharmacological properties of this latter subunit. With the feasibility of producing large amounts of ChTX by recombinant techniques and the knowledge of the three-dimensional structure of the peptide, it has been possible to carry out site-directed mutagenesis studies and obtain a picture of the interaction surface of the toxin with two channels, maxi-K and Shaker, and to derive a picture of the complementary surface of the receptor in these two channels. Finally, ChTX, and the more selective K+ channel toxins that were subsequently discovered, have provided us with unique tools not only to determine the functional role that K+ channels play in target tissues but also to develop the molecular pharmacology of these channels.