Functional characterization of zebrafish Kcnh2a splice variants reveals distinct gating properties

Zebrafish have emerged as an important vertebrate model for ion channel research. Human KCNH2 channels, commonly known as hERG channels, play critical roles in cardiac repolarization and are closely associated with inherited and acquired arrhythmia syndromes. In contrast, cardiac repolarization in zebrafish is primarily mediated by Kcnh6 channels, and the physiological properties of zebrafish Kcnh2 channels remain largely unknown. PCR analysis revealed that zebrafish kcnh2 is preferentially expressed in the brain, whereas kcnh6 is enriched in the heart, suggesting distinct physiological roles of ERG family channels in zebrafish. In the present study, we cloned the full-length zebrafish kcnh2a-201 (z2a-201) and its splice variant, kcnh2a-202 (z2a-202), and examined their electrophysiological properties using two-electrode voltage-clamp recordings in Xenopus oocytes. Both zebrafish Kcnh2a channels generated characteristic hERG-like currents with amplitudes comparable to those of hERG1a channel. However, compared with hERG1a channels, both zebrafish channels exhibited negatively shifted voltage-dependent activation, accelerated activation kinetics, and markedly slowed deactivation kinetics. In addition, zebrafish Kcnh2a channels showed depolarized voltage dependence of inactivation together with faster inactivation kinetics. Furthermore, z2a-201 and z2a-202 channels displayed distinct deactivation properties, suggesting functional diversification between splice variants. These findings characterize the electrophysiological properties of zebrafish Kcnh2a splice variants and provide a foundation for future studies investigating the non-cardiac and neuronal functions of KCNH2 channels.