Ether ℵ go-go Potassium Channels KCNH1 and KCNH5 Have Four Functional Orthologs in Danio Rerio

Abstract

The human ether a go-go channels KCNH1 and KCNH5 form a subgroup with unique functional properties within the eight-membered KCNH family of voltage-gated potassium channels. In mammals, the expression of both genes is mainly restricted to the brain, implying a role in electrical signaling of neurons. Heterologous expression in mammalian cells and Xenopus oocytes revealed that ether a go-go channels are sensitive to intracellular Ca2+/calmodulin. The second functional characteristic of both channels is a pronounced slowing of activation kinetics upon binding of extracellular divalent cations. To elucidate the physiological relevance of such properties, an adequate model organism would be desirable. Here we studied the expression of ether a go-go orthologs in zebrafish. Due to a whole-genome duplication during evolution of teleost fish, mammalian genes can have two functional orthologs in zebrafish. However, for the majority of duplicated genes, one gene copy is lost or present as nonfunctional pseudogene only. Using in silico screening of genome databases and cloning from reverse transcribed mRNA, we could show that for each of the two human ether a go-go channels two functional orthologs exist in zebrafish. Upon expression in Xenopus oocytes, all four genes generated functional channels with current-voltage relationships similar to the human orthologs, characterized by a very negative threshold of the activation voltages. A more pronounced slowing of activation kinetics in the presence of extracellular Mg2+ ions clearly distinguished KCNH5 and its two fish orthologs from human KCNH1 and the corresponding fish channels. In summary, the structural and functional conservation between human and fish ether a go-go channels makes zebrafish a promising model, but gene duplication must be taken into account. This may also be relevant for the closely related paralogs ERG and ELK.