Sorcin Regulates Excitation-Contraction Coupling in the Heart

The Ohio State University, Columbus, Ohio, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2003; 278(31):28865-71. DOI: 10.1074/jbc.M302009200
Source: PubMed


Sorcin is a penta-EF hand Ca2+-binding protein that associates with both cardiac ryanodine receptors and L-type Ca2+ channels and has been implicated in the regulation of intracellular Ca2+ cycling. To better define the function of sorcin, we characterized transgenic mice in which sorcin was overexpressed in the heart. Transgenic mice developed normally with no evidence of cardiac hypertrophy and no change in expression of other calcium regulatory proteins. In vivo hemodynamics revealed significant reductions in global indices of contraction and relaxation. Contractile abnormalities were also observed in isolated adult transgenic myocytes, along with significant depression of Ca2+ transient amplitudes. Whole cell ICa density and the time course of activation were normal in transgenic myocytes, but the rate of inactivation was significantly accelerated. These effects of sorcin on L-type Ca2+ currents were confirmed in Xenopus oocyte expression studies. Finally, we examined the expression of sorcin in normal and failing hearts from spontaneous hypertensive heart failure rats. In normal myocardium, sorcin extensively co-localized with ryanodine receptors at the Z-lines, whereas in myopathic hearts the degree of co-localization was markedly disrupted. Together, these data indicate that sorcin modulates intracellular Ca2+ cycling and Ca2+ influx pathways in the heart.

Download full-text


Available from: Sylvia A Mccune, Jan 06, 2016
  • Source
    • "Discordant effects of sorcin overexpression on cardiac function have been reported. According to Seidler et al. [13] and Meyers et al. [19] cardiac-specific overexpression of sorcin in rabbit myocytes and transgenic mice leads to a significant reduction in contractility, while Suarez et al. [20] and Frank et al. [21] reported that transfection of rat or mouse heart or isolated cardiac cells with sorcin-expressing vectors significantly enhanced cardiac function. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Sorcin is a penta-EF-hand protein that interacts with intracellular target proteins after Ca(2+) binding. The sarcolemmal Na(+)/Ca(2+) exchanger (NCX1) may be an important sorcin target in cardiac muscle. In this study, RNAi knockdown of sorcin, purified sorcin or sorcin variants was employed in parallel measurements of: (i) NCX activity in isolated rabbit cardiomyocytes using electrophysiological techniques and (ii) sorcin binding to the NCX1 calcium binding domains (CBD1 and (iii) using surface plasmon resonance and gel overlay techniques. Sorcin is activated by Ca(2+) binding to the EF3 and EF2 regions, which are connected by the D helix. To investigate the importance of this region in the interaction with NCX1, three variants were examined: W105G and W99G, mutated respectively near EF3 and EF2, and E124A that does not bind Ca(2+) due to a mutation at EF3. Downregulation of sorcin decreased and supplementation with wt sorcin (3muM) increased NCX activity in isolated cardiomyocytes. The relative stimulatory effects of the sorcin variants were: W105G>wt sorcin>Sorcin Calcium Binding Domain (SCBD)>W99G>E124A. Sorcin binding to both CBD1 and 2 was observed. In the presence of 50microM Ca(2+), the interaction with CBD1 followed the order W105G>SCBD>wt sorcin>W99G>E124A. In sorcin, the interacting surface can be mapped on the C-terminal Ca(2+)-binding domain in the D helix region comprising W99. The fast association/dissociation rates that characterize the interaction of sorcin with CBD1 and 2 may permit complex formation/dissociation during an excitation/contraction cycle.
    Full-text · Article · Mar 2010 · Journal of Molecular and Cellular Cardiology
  • Source
    • "By interacting with these targets, sorcin modifies excitation– contraction (E–C) coupling by increasing NCX activity and reducing RyR2 activity (Meyers et al. 2003; Seidler et al. 2003). Sorcin is also implicated in the regulation of both Ca 2+ -dependent and voltage-dependent inactivation mechanisms of L-type Ca 2+ current (I Ca,L ; CDI and VDI), which regulates Ca 2+ influx into the cell (Meyers et al. 2003). Meyers and co-workers (1998) describe the binding of sorcin to the C−terminus of the LTCC, but the mechanism by which sorcin modulates Ca 2+ influx via I Ca,L activity, particularly via current inactivation, is not clearly understood. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We examined the modulation of the cardiac L-type Ca(2+) channel (LTCC) by the regulatory protein sorcin and tested the hypothesis that modulation occurred by direct interaction. Whole-cell patch-clamp recordings were made on native rabbit ventricular myocytes and HEK 293 cells expressing cardiac alpha(1C) subunits. In ventricular cells, sorcin increased peak current when using either Ca(2+) or Ba(2+) as charge carriers. In HEK 293 cells, sorcin increased peak current density when using Ba(2+) as a charge carrier but not when using Ca(2+). In ventricular myocytes, current inactivation (tau(fast), in ms) was slowed by sorcin with Ca(2+) as the charge carrier, whilst in the presence of Ba(2+) it was enhanced. In HEK 293 cells, sorcin significantly enhanced tau(fast), but no significant change was observed with Ba(2+). This trend was mimicked by the truncated peptide, sorcin Ca(2+)-binding domain, which lacks the N-terminal domain. These data suggest that sorcin interacts with LTCC via its C-terminal domain, which alters current magnitude and tau(fast). These effects appear to be influenced by the prevailing experimental conditions.
    Full-text · Article · Aug 2008 · Experimental Physiology
    • "coupling and, in particular, contributes to terminating cardiac contraction (Zamparelli et al., 2000; Meyers et al., 2003; Farrell et al., 2004). Indeed, transgenic mice carrying the F112L missense mutation in the critical D helix–EF3 loop calcium binding region display defective excitation–contraction coupling in the heart (Collis et al., 2007). "
    Article: Sorcin
    [Show abstract] [Hide abstract]
    ABSTRACT: Sorcin participates in calcium-dependent signaling in many tissues. Upon calcium binding, sorcin undergoes a conformational change which determines exposure of hydrophobic surfaces and results in a reversible translocation to membranes, where sorcin interacts with several specific target proteins, thereby converting the calcium signal into different cellular processes. In the heart, sorcin participates in the transition between the contraction and relaxation events.
    No preview · Article · Jan 2008 · Calcium Binding Proteins
Show more