Expression and function of KCNQ channels in larval zebrafish

Members of the Kv7 family generate a sub-threshold potassium current, termed M-current, that regulates the excitability of principal central neurons. Mutations in two members of this family, Kv7.2 (KCNQ2) and Kv7.3 (KCNQ3) are associated with a neurological disorder known as benign familial neonatal convulsion (BFNC). Despite their importance in normal and pathological brain function, developmental expression and function of these channels remains relatively unexplored. Here, we examined the temporal expression of Kv7 channel subunits in zebrafish larvae using a real-time quantitative PCR approach. Spatial expression in the larval zebrafish brain was assessed using whole-mount in situ hybridization. The mRNA for three members of the Kv7 family (KCNQ2, 3 and 5) is reported in zebrafish between 2 and 7 days post-fertilization (dpf). Using electrophysiological techniques, we show that inhibitors of Kv7 channels (linopirdine and XE991) induce burst discharge activity in immature zebrafish between 3 and 7 dpf. This abnormal electrical activity is blocked by a Kv7 channel opener (retigabine) and was also shown to evoke convulsive behaviors in freely swimming zebrafish. Using morpholino oligonucleotides directed against KCNQ3, we confirmed a role for KCNQ channels in generation of electrical burst discharges. These results indicate that functional Kv7 channels are expressed in the larval zebrafish nervous system and could play a direct role in generation of seizure activity.