Calmodulin Interferes with Ca v1.2 C-Terminal Regulation of L-Type Channel Current

Abstract

The L-type Ca channel (CaV1.2) distal carboxyl-terminus (CCt) has multiple functions. CCt inhibits L-type channel current, and is a mobile element that translocates to the nucleus where it regulates CaV1.2 transcription. CCt interacts with CaV1.2 in a similar domain as calmodulin (CaM). The purpose of this study is test the hypothesis that CaM and CCt compete for functional interaction with CaV1.2. CaV1.2 calcium current (ICa,L) and barium current (IBa,L) were recorded from HEK 293 cells transfected with CaV1.2 + CaVbeta2a. This background was compared to cells additionally transfected with CaM and/or CCt. The CaV1.2 expressed was deleted at position 1733 or 1801 (numbering based on rabbit sequence), and CCt corresponded to amino acids 1821-2171. CCt co-expression significantly reduced IBa,L, but not ICa,L. CCt inhibition of ICa,L is reversed by exogenous CaM co-expression, but not by calcium binding deficient apo-CaM. Examination of the peak I(V) curves suggests that midpoint of activation was not affected. Mouse ventricular cardiomyocytes transfected with CCt also showed a reduction in Cav1.2 IBa,L, but no reduction in ICa,L. Exogenous CaM co-expression also relieved CCt auto-inhibiton in mouse ventricular cardiomyocytes. We conclude that CCt attenuation of current occurs only with Ba, and is consistent with a Ca alleviation of CCt block. Thus, CaM and Ca functionally compete to limit CCt auto-inhibition of CaV1.2 current.