It is also possible that the β or α2δ auxiliary subunits, which also modulate calcium channel function and have previously been shown to be regulated by phosphorylation (Viard et al., 2004), are additional Cdk5 substrates that can modify CaV2.2 and SNARE protein interactions. We demonstrated that Cdk5 impacts CaV2.2 channel availability and channel open probability. It will be intriguing to further elucidate how Cdk5-mediated phosphorylation of CaV2.2 may result

in conformational alterations between the α1 subunit and other channel subunits, or potentially with the pore-forming domain, to influence channel gating properties. In line with previous reports, overexpression of CaV2.2 did not affect the CaV2.1 (P/Q-type calcium channel) current (Cao and Tsien, 2010). However, in our study, acute slices expressing WT CaV2.2 HSV exhibited decreased DAPT datasheet PPF, which is in agreement with some previous findings (Ahmed and Siegelbaum,

2009) but in contrast to others, in which no alterations in PPF were observed (Cao and Tsien, 2010). This may be due to differences in Schaffer collateral field recordings versus single-cell recordings of dissociated hippocampal neurons. Thus, in future studies it will be important to further probe how Cdk5-mediated phosphorylation of CaV2.2 affects its contribution to excitatory postsynaptic currents. As Cdk5 and CaV2.2 are present in GABAergic interneurons (Poncer et al., 1997; Rakić et al., 2009), it would also be interesting to determine whether Cdk5 differentially affects excitatory and inhibitory neurotransmission. Combined with those of previous studies, our data suggest that both CaV2.2 and Cdk5 mediate presynaptic plasticity by regulating RAD001 concentration neurotransmitter release. Recent literature suggests

that Cdk5 is a central regulator of synaptic homeostasis. Cdk5 activity is required for the downregulation of heightened synaptic activity via phosphorylation of the postsynaptic protein SPAR. This priming effect allows Polo-like Non-specific serine/threonine protein kinase kinase 2 to promote the degradation of SPAR during homeostatic scaling (Seeburg et al., 2008). Cdk5 also serves as a control point for neurotransmission, as inhibition of Cdk5 activity by roscovitine results in access to the resting synaptic vesicle pool (Kim and Ryan, 2010). Furthermore, Cdk5 activity is critical for the presynaptic adaptation of hippocampal CA3 recurrent circuitry under chronic inactivity, as it mediates reduced connectivity after silencing synapses but enhances synaptic strength of the remaining connections (Mitra et al., 2011). Precisely how levels of Cdk5, and Cdk5/p35 activity, are regulated under physiological or excitotoxic conditions to impart its action on CaV2.2 in specific cell populations remains an exciting topic for future work, which may also reveal additional CaV2.2 binding partners, as well as Cdk5 substrates that play a vital role in synaptic homeostasis. In summary, our data demonstrate a previously uncharacterized interaction between CaV2.