Of the ～22,000 protein-coding genes in the human genome, an estimated 8,000 are druggable (1). The current drug market targets no more than 450 unique human proteins (1) and many contain antihypertensive, antineoplastic, or anti-inflammatory effects. Receptors, enzymes, and transporter proteins comprise most of the targets. The following protein families are overrepresented: rhodopsin- like G protein-coupled receptors, voltagegated ion channels, and ligand-gated ion channels (1). Their membrane localization, diverse tissue distribution, and the critical roles played by ion channels in human physiology makes these proteins attractive targets for drug discovery (2). Although worldwide sales of ion channel-targeted drugs are over US$10 billion, ion channels remain significantly underexploited as therapeutic targets (3).
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