INTRODUCTION: Voltage-gated potassium (Kv) channels are essential for maintaining the resting membrane potential. Mutations in Kv2.1 channels have been implicated in developmental epileptic encephalopathy. Previous analysis of mutations in zebrafish genes encoding the Kv2.1 subunits (kcnb1 and kcng4b) has shown their antagonising roles in the development of hollow organs.

AIM(S): In this study, we investigate the effects of kcnb1 mutations in zebrafish by examining the behaviour and neurophysiology of kcnb1 loss-of-function (LOF, kcnb1sq301) and gain-of-function (GOF, kcng4bwaw304) mutants.

METHOD(S): Zebrafish larvae at 5 days post fertilisation (dpf) were assessed using behavioural assays like spontaneous locomotor activity, and pentylenetetrazole (PTZ) exposure. Additionally, response to light was assessed via multiple behavioural paradigms. Quantitative PCR (qPCR) was performed for genes implicated in epilepsy and electrophysiological activity was recorded from the optic tectum and retina.

RESULTS: Both LOF and GOF mutants exhibit hypoactivity under light conditions. Upon exposure to 5 mM PTZ, locomotor activity increases and seizures start. Analysis using qPCR revealed increased c-fos and gad2 transcript levels, but decreased gabra1 transcript level, suggesting impaired inhibitory neurotransmission. Electrophysiology recordings from the tectum show spontaneous electrical activity in the mutants under baseline conditions. The LOF mutant also exhibited light sensitivity characterised by freezing responses under high-intensity light. Electroretinography revealed loss of retinal activity in the LOF variant.

CONCLUSIONS: These findings indicate that the defects in the Kv2.1 subunits predispose the larvae to PTZ susceptibility, affecting locomotor behaviour and leading to disruption of inhibitory neurotransmission. Moreover, a reduction in the photomotor response in the LOF variant, along with loss of retinal electrical activity, suggests photosensitivity and highlights the role of kcnb1 in visual processing.

FINANCIAL SUPPORT: This work has been supported by the Polish National Science Centre OPUS grant UMO-2020/39/B/NZ3/02729