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Circulation Research. 2009
Published online before print May 21, 2009, doi: 10.1161/CIRCRESAHA.109.196972
A more recent version of this article appeared on June 19, 2009
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Submitted on January 16, 2009
Revised on March 31, 2009
Accepted on May 11, 2009

The Accessory Subunit KChIP2 Modulates the Cardiac L-Type Calcium Current

Morten B. Thomsen ; Chaojian Wang ; Nazira Özgen ; Hong-Gang Wang ; Michael R. Rosen ; and Geoffrey S. Pitt *

From the Departments of Pharmacology (M.B.T., M.R.R.) and Pediatrics (N.O., M.R.R.), College of Physicians and Surgeons, Columbia University, New York; and Ion Channel Research Unit, Department of Medicine (C.W., H.-G.W., G.S.P.), Duke University Medical Center, Durham, NC.

* To whom correspondence should be addressed. E-mail: geoffrey.pitt{at}duke.edu.

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 (KChIP)2, 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 {alpha}1C subunit N terminus. We found that KChIP2 binds to the N-terminal inhibitory module of {alpha}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.


Key words: ion channels • mouse models • amino terminal inhibitory module • auxiliary subunit • CaV1.2