Identification of novel small molecule modulators of K_2P18.1 two-pore potassium channel

Two-pore domain potassium (K_2P) channels are responsible for background potassium (K⁺) current, which is crucial for the maintenance of resting membrane potential. K_2P18.1, also called TWIK-related spinal cord K⁺ channel (TRESK) or KCNK18, is thought to be a major contributor to background K⁺ currents, particularly in sensory neurons where it is abundantly expressed. Despite its critical role and potential therapeutic implication, pharmacological tools for probing K_2P18.1 activity remain unavailable. Here, we report a high-throughput screen against a collection of bioactive compounds that yielded 26 inhibitors and 8 activators of K_2P18.1 channel activity with more than 10-fold selectivity over the homologous channel K_2P9.1. Among these modulators, the antihistamine loratadine inhibited K_2P18.1 activity with IC₅₀ of 0.49±0.23 μM and is considerably more potent than existing K_2P18.1 inhibitors. Importantly, the inhibition by loratadine remains equally efficacious upon potentiation of K_2P18.1 by calcium signaling. Furthermore, the loratadine effect is dependent on transmembrane residues F145 and F352, providing orthogonal evidence that the inhibition is caused by a direct compound-channel interaction. This study reveals new pharmacological modulators of K_2P18.1 activity useful in dissecting native K_2P18.1 function.