Inactivation of L-type calcium channel modulated by HCN2 channel

Abstract

Ca2+ entry is delicately controlled by inactivation of L-type calcium channel (LTCC) composed of the pore-forming subunit α1C and the auxiliary subunits β1 and α2δ. Calmodulin is the key protein that interacts with the COOH-terminal motifs of α1C, leading to the fine control of LTCC inactivation. In this study we show evidence that a hyperpolarization-activated cyclic nucleotide-gated channel, HCN2, can act as a nonchannel regulatory protein to narrow the L-type Ca2+ channel current-voltage curve. In the absence of LTCC auxiliary subunits, HCN2 can induce α1C inactivation. Without α2δ, HCN2-induced fast inactivation of α1C requires calmodulin. With α2δ, the α1C/HCN2/α2δ channel inactivation does not require calmodulin. In contrast, β1-subunit plays a relatively minor role in the interaction of α1C with HCN2. The NH2 terminus of HCN2 and the IQ motif of α1C subunit are required for α1C/HCN2 channel interaction. Ca2+ channel inactivation is significantly slowed in hippocampus neurons (HNs) overexpressing HCN2 mutant lacking NH2 terminus and accelerated in HNs overexpressing the wild-type HCN2 compared with HN controls. Collectively, these results revealed a potentially novel protection mechanism for achieving the LTCC inactivation via interaction with HCN2.