Functional characterization of zebrafish K2P18.1 (TRESK) two-pore-domain K+ channels

The human KCNK18 gene is predominantly expressed in brain, spinal cord, and dorsal root ganglion neurons. Encoded K2P18.1K(+) channels are functionally implicated in migraine, pain and anesthesia. Data delineating the in vivo significance of K2P18.1 are still limited owing to a lack of model systems allowing for rapid, whole organism phenotypic analyses. We hypothesized that zebrafish (Danio rerio) might close this scientific gap. This work was designed to characterize the zebrafish ortholog of K2P18.1 in comparison to human K2P18.1 channels. The complete coding sequence of zKCNK18 was amplified from zebrafish cDNA. Zebrafish KCNK18 expression was assessed by in situ hybridization. Human and zebrafish K2P18.1 currents were functionally analyzed using two-electrode voltage clamp electrophysiology and the Xenopus oocyte expression system. KCNK18 mRNA is expressed in zebrafish brain and eyes. Human and zebrafish K2P18.1 proteins share 32 % identity. Zebrafish K2P18.1 channels mediate K(+)-selective background currents that stabilize the negative resting membrane potential. Functional similarities between human and zK2P18.1 currents include open rectification properties, inhibition by barium, and regulation by signaling molecules protein kinase (PK)C, PKA, and phospholipase C. In contrast to the human ortholog, zK2P18.1 exhibited reduced sensitivity to elevation of intracellular calcium levels by ionomycin and was virtually insensitive to inhibition by quinidine. Zebrafish and human K2P18.1 channels share functional and regulatory properties, indicating that the zebrafish may serve as model to assess K2P18.1 function in vivo. However, distinct differences in K2P18.1 current regulation require careful consideration when zebrafish data are extrapolated to human physiology.