Cloning and characterization of zebrafish K_2P13.1 (THIK-1) two-pore-domain K⁺ channels

Two-pore-domain potassium (K_2P) channels conduct background potassium currents in the heart and other tissues. K_2P currents are involved in the repolarization of action potentials and stabilize the resting membrane potential. Human K_2P13.1 (THIK-1) channels are expressed in the heart and have recently been implicated in atrial fibrillation. The in vivo significance of K_2P13.1 currents in cardiac electrophysiology is not known. We hypothesized that Danio rerio (zebrafish) may serve as model to elucidate the functional role of cardiac K_2P13.1 channels. This work was designed to characterize zebrafish orthologs of K_2P13.1. Two zkcnk13 coding sequences were identified by DNA database searches and amplified from zebrafish cDNA. Human and zebrafish K_2P13.1 proteins exhibit 70% (K_2P13.1a) and 66% (K_2P13.1b) identity. Kcnk13 expression in zebrafish was studied using polymerase chain reaction. Zebrafish kcnk13a and zkcnk13b mRNAs were detected in brain and heart. Human and zebrafish K_2P13.1 currents were analyzed in the Xenopus oocyte expression system by voltage clamp electrophysiology. Zebrafish K_2P13.1a polypeptides were non-functional, while zK_2P13.1b channels exhibited K⁺ selective, outwardly rectifying currents. Zebrafish and human K_2P13.1 currents were similarly activated by arachidonic acid and reduced by barium, mexiletine, lidocaine, and inhibition of phospholipase C. In conclusion, zebrafish K_2P13.1b channels and their human orthologs exhibit structural and regulatory similarities. Zebrafish may be used as in vivo model for the assessment of physiology and therapeutic significance of K_2P13.1.