Abstract
An astroglial inwardly rectifying K+ channel, Kir4.1, is inhibited by a variety of compounds including a number of antidepressants. The mechanisms for the channel-drug interaction are however poorly understood. Here we identified electrophysiologically amino acids at the Kir4.1 pore essential for binding with antidepressants, fluoxetine, a SSRI, and nortrytyline, a tricyclic antidepressant, using the chimera and alanine-substituted mutants. Wild-type and mutant rat Kir4.1 channels were expressed in Xenopus oocytes. Mutagenesis experiments revealed that two amino acids, Thr128 and Glu158 on TM2, are indispensable for both of fluoxetine and nortriptyline to inhibit Kir4.1 channel current. Homology modeling of Kir4.1 channel pore using Shaker pore as the template suggests that both Thr128 and Glu158 face the central cavity of the channel in the open and closed states. Thr128 and Glu158 are thought to interact with respectively hydrogen bond acceptor and constitutively charged regions of drugs. Further computational analysis for common features in Kir4.1 blockers revealed that at least four pharmacophores distribute in the drugs. Two of them may function in hydrogen bonding and electrostatic interaction. The pharmacophores locate within a geometrical range between Thr128 and Glu158 to be retained in central cavity of the channel. These findings strongly support the drug binding in its position. [J Physiol Sci. 2008;58 Suppl:S75]
