Involvement of CaV2.2 channels and α2δ-1 in hippocampal homeostatic synaptic plasticity

In the mammalian brain, presynaptic CaV2 channels play a pivotal role for synaptic transmission by mediating fast neurotransmitter exocytosis via influx of Ca2+ into the active zone of presynaptic terminals. However, the distribution and modulation of CaV2.2 channels at highly plastic hippocampal synapses remains to be elucidated. Here, we assess CaV2.2 channels during homeostatic synaptic plasticity, a compensatory form of homeostatic control preventing excessive or insufficient neuronal activity during which extensive active zone remodelling has been described. We show that chronic silencing of neuronal activity in mature hippocampal cultures resulted in elevated presynaptic Ca2+ transients, mediated by increased levels of CaV2.2 channels at the presynaptic site. This work focussed further on the role of 2{delta}-1 subunits, important regulators of synaptic transmission and CaV2.2 channel abundance at the presynaptic membrane. We find that 2{delta}-1-overexpression reduces the contribution of CaV2.2 channels to total Ca2+ flux without altering the amplitude of the Ca2+ transients. Levels of endogenous 2{delta}-1 decreased during homeostatic synaptic plasticity, whereas the overexpression of 2{delta}-1 prevented homeostatic synaptic plasticity in hippocampal neurons. Together, this study reveals a key role for CaV2.2 channels and novel roles for 2{delta}-1 during synaptic plastic adaptation.