Ca2+-dependent regulation of synaptic δ2 glutamate receptor density in cultured rat Purkinje neurons

The delta2 glutamate receptor (delta2 receptor), which is expressed abundantly at parallel fibre-Purkinje neuron synapses, has an important role in synaptogenesis and synaptic plasticity in the cerebellum. The present study examined the molecular mechanisms regulating synaptic delta2 receptor density. Immunocytochemistry, using two antibodies against the intracellular C-terminal and extracellular N-terminal regions of the delta2 receptor, indicated the reversible redistribution of postsynaptic delta2 receptors in response to either glutamatergic stimulation or enhancement of synaptic activity. The effect of glutamatergic stimulation was completely inhibited by either coapplication of the glutamate receptor antagonist or the removal of extracellular Ca2+ using EGTA and mimicked by selective activation of voltage-gated Ca2+ channels (VGCCs) with KCl, suggesting the significant role of Ca2+ influx in delta2 receptor redistribution. Biochemical examination indicated that a large amount of delta2 receptor protein was internalized following glutamatergic stimulation. These results suggest that the number of synaptic delta2 receptors is controlled by endocytosis in a synaptic activity- and intracellular Ca2+-dependent way, through which synaptogenesis and synaptic plasticity in Purkinje cells might be modulated.