Zebrafish express CaMKII isoforms that are involved in the modulation of AMPA currents in Mauthner neurons

Glutamate AMPA receptors (AMPARs) are major excitatory receptors in the vertebrate CNS. Phosphorylation of AMPARs has been shown to be an important mechanism for controlling the function of these receptors in synaptic transmission and synaptic plasticity. We previously showed that fast excitatory synaptic transmission in zebrafish Mauthner neurons is mediated predominantly by AMPARs. We are investigating the mechanisms that underlie the maturation of glutamatergic synapses and wanted to determine if CaMKII, which is expressed in developing zebrafish, might play a role in the normal development of AMPA receptor‐containing synapses. Western blot analysis indicates that zebrafish express CaMKII (~50 kDa in size). We used whole cell patch clamp electrophysiology to record AMPA miniature excitatory postsynaptic currents (AMPA‐mEPSCs) from Mauthner cells (M‐cells) of developing zebrafish. mEPSCs were recorded in the presence of elevated K + (10 mM K + ) that was used to enhance synaptic activity. Pipette application of the general CaMK inhibitor, KN‐62 (10 μM), and the specific CaMKII blocker, AIP (5 μM) blocked the effects of high K + on mEPSC amplitude. Both CaMK inhibitors affect the kinetics of AMPA currents but not the frequency. Our results suggest that CaMKII may be involved in the synaptic activity‐induced enhancement of AMPA mEPSC amplitude in zebrafish. This research was funded by the NSERC of Canada.