M. B Thomsen, C Wang, N Ozgen, H. G Wang, M. R Rosen and G. S. Pitt
Circulation Research, 2009, 104(12), 1382-1389. DOI: 10.1161/CIRCRESAHA.109.196972
Complex modulation of voltage-gated Ca2+ currents through the interplay among Ca2+ channels and various Ca2+-binding proteins is increasingly being recognized. The K+ channel interacting protein 2 (KChIP2), originally identified as an auxiliary subunit for KV4.2 and a component of the transient outward K+ channel (Ito), is a Ca2+-binding protein whose regulatory functions do not appear restricted to KV4.2. Consequently, we hypothesized that KChIP2 is a direct regulator of the cardiac L-type Ca2+ current (ICa,L). We found that ICa,L density from KChIP2–/– myocytes is reduced by 28% compared to ICa,L recorded from wild-type myocytes (P<0.05). This reduction in current density results from loss of a direct effect on the Ca2+ channel current, as shown in a transfected cell line devoid of confounding cardiac ion currents. ICa,L regulation by KChIP2 was independent of Ca2+ binding to KChIP2. Biochemical analysis suggested a direct interaction between KChIP2 and the CaV1.2 1C subunit N terminus. We found that KChIP2 binds to the N-terminal inhibitory module of 1C and augments ICa,L current density without increasing CaV1.2 protein expression or trafficking to the plasma membrane. We propose a model in which KChIP2 impedes the N-terminal inhibitory module of CaV1.2, resulting in increased ICa,L. In the context of recent reports that KChIP2 modulates multiple KV and NaV currents, these results suggest that KChIP2 is a multimodal regulator of cardiac ionic currents.