Accessory Subunit KChIP2 Modulates the Cardiac L-Type Calcium Current

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

Abstract

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 K_V4.2 and a component of the transient outward K⁺ channel (I_to), is a Ca²⁺-binding protein whose regulatory functions do not appear restricted to K_V4.2. Consequently, we hypothesized that KChIP2 is a direct regulator of the cardiac L-type Ca²⁺ current (I_Ca,L). We found that I_Ca,L density from KChIP2^–/– myocytes is reduced by 28% compared to I_Ca,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. I_Ca,L regulation by KChIP2 was independent of Ca²⁺ binding to KChIP2. Biochemical analysis suggested a direct interaction between KChIP2 and the Ca_V1.2 _1C subunit N terminus. We found that KChIP2 binds to the N-terminal inhibitory module of _1C and augments I_Ca,L current density without increasing Ca_V1.2 protein expression or trafficking to the plasma membrane. We propose a model in which KChIP2 impedes the N-terminal inhibitory module of Ca_V1.2, resulting in increased I_Ca,L. In the context of recent reports that KChIP2 modulates multiple K_V and Na_V currents, these results suggest that KChIP2 is a multimodal regulator of cardiac ionic currents.

ASCI-ID: 1434-34