The K_V11.1 (HERG) channel is a member of the ether-a-go-go (EAG) subfamily of voltage-dependent K⁺ channels that includes the related proteins K_V11.2 and K_V11.3 (erg2 and erg3). K_V11.1 possesses the signature structure of the voltage-dependent K⁺ channels: six membrane-spanning domains and intracellular N- and C-termini.

The K_V11.1 current is characterized by strong inward rectification with slow activation and very rapid inactivation kinetics. The channel is expressed in the brain and heart (where it underlies the I_Kr current) and has a central role in mediating repolarization of action potentials.^1,2

Mutations in the K_V11.1 channel cause inherited long QT syndrome (LQTS) or abnormalities in the repolarization of the heart that are associated with life-threatening arrhythmias and sudden death. All the identified K_V11.1 mutations produce loss of function of the channel via several cellular mechanisms ranging from alterations of gating properties, alterations of channel permeability/selectivity and alterations in intracellular channel trafficking that decreases the number of channels that reach the cell membrane.^1,2 

Recently, drug-induced forms of LQTS have been reported for a wide range of non-cardiac drugs including antihistamines, psychoactive agents and antimicrobials. All these drugs potently block the K_V11.1 channel as an unintended side effect, prompting regulatory drug agencies to issue recommendations for the testing of new drugs for their potential K_V11.1 blocking effect.

In addition, K_V11.1 expression was found to be upregulated in several tumor cell lines of different histogenesis, suggesting that it confers the cells some advantage in cell proliferation. Indeed, in several studies it has been shown that inhibition of the K_V11.1 current leads to a decrease in tumor cell proliferation.³