Mechanistic insights into robust cardiac I(Ks) potassium channel activation by aromatic polyunsaturated fatty acid analogues

Voltage-gated potassium (K(V)) channels are important regulators of cellular excitability and control action potential repolarization in the heart and brain. K(V) channel mutations lead to disordered cellular excitability. Loss-of-function mutations, for example, result in membrane hyperexcitability, a characteristic of epilepsy and cardiac arrhythmias. Interventions intended to restore K(V) channel function have strong therapeutic potential in such disorders. Polyunsaturated fatty acids (PUFAs) and PUFA analogues comprise a class of K(V) channel activators with potential applications in the treatment of arrhythmogenic disorders such as Long QT Syndrome (LQTS). LQTS is caused by a loss-of-function of the cardiac I(Ks) channel - a tetrameric potassium channel complex formed by K(V)7.1 and associated KCNE1 protein subunits. We have discovered a set of aromatic PUFA analogues that produce robust activation of the cardiac I(Ks) channel and a unique feature of these PUFA analogues is an aromatic, tyrosine head group. We determine the mechanisms through which tyrosine PUFA analogues exert strong activating effects on the I(Ks) channel by generating modified aromatic head groups designed to probe cation-pi interactions, hydrogen bonding, and ionic interactions. We found that tyrosine PUFA analogues do not activate the I(Ks) channel through cation-pi interactions, but instead do so through a combination of hydrogen bonding and ionic interactions.