Electrostatic Interactions Of Negatively Charged Dhaa Derivatives With The Voltage-Gated Potassium Channel Kv7.2/7.3

Many patients with epilepsy do not respond to existing pharmaceutical treatment, so there is a large need of new types of antiepileptic drugs. The voltage dependent M-type potassium current activates and deactivates slowly and is important to set the resting potential and to reduce repetitive firing of neurons. This current is generated by an ion channel composed of Kv7.2 and 7.3 subunits. Some inherited forms of epilepsy are caused by mutations in the genes coding for these subunits, and the Kv7.2/7.3 channel is a validated target for antiepileptic drugs. Today, there is no Kv7.2/7.3 channel-opening drug on the market. Our goal is to develop a Kv7.2/7.3-channel opening compound. Recently, our group designed a set of molecules, based on the structure of dehydroabietic acid (DHAA), that open the Shaker Kv channel from Drosophila melanogaster. We showed that he charge of the carboxyl group of the DHAA derivatives as well as potitively charged amino-acid residues of the channel's voltage sensor are required for the compounds to open the channel. In previous experiments we showed that DHAA-derivatives at concentrations as low as 0.3 μM open of the human hKv7.2/7.3 channel but it is not known if the mechanism is the same as for the Shaker Kv channel. Here we explored if the same mechanism is valid for the hKv7.2/7.3 channel expressed in Xenopus oocytes. To explore the role of the charge of the carboxyl group we tested the effect of the compounds at different pH. To explore the role of the charges of the voltage sensor S4 we systematically mutated the extracellular end of S4. Overall, the mechanism of DHAA derivatives on the hKv7.2/7.3 channel is the same as for the Shaker Kv channel, but there are quantitative differences.