Investigating the characteristics of drug binding to the inner cavity of hERG potassium channels

The human Ether à-go-go Related Gene (hERG) channel makes up the pore forming subunit of the IKr channel. This channel is involved in the repolarisation of the cardiac action potential. Reduction in IKr may cause the prolongation of the action potential, leading to fatal arrhythmias. A large variety of potentially therapeutic compounds inhibit the IKr channels, leading to acquired long QT syndrome. Therefore characterisation of the channel and improvements to in silico models are needed to accurately predict potential hERG side effects. The aim of this project was to use a series of analogues to block the hERG K+ channel, using them as molecular rulers to measure the size of the inner cavity. The phenotype of block was examined to see whether increasing length, results in a change in the phenotype of block from a drug trapping type to a foot in the door one. This would have given an estimate of the size of the hERG inner cavity. Excised inside-out patches of hERG channels display a significant rundown with time after excision. The project also investigated the region of hERG responsible for rundown. A chimeric channel between hERG and bEAG, a closely related channel that does not display rundown, was produced. The aim was to produce a channel with hERG properties, but without the rundown characteristic. This chimeric channel could then be used in excised inside-out patch recordings. The series of derivatives were found to have high affinity to the hERG channel. However, they displayed unusual blocking characteristics, inhibiting the channel in the open state, yet unbound in the closed state. It was also found that the C-terminus of hERG appears to be responsible for the rundown characteristic. The exchange for that of bEAG resulted in a channel that had attenuated rundown.