The cardiac sarcolemmal Na-Ca exchanger (NCX) is the primary mechanism for the extrusion of Ca from myocytes. As such, the exchanger is an important regulator of intracellular Ca and cardiac contractility. The continuing long-term objective of this renewal is to further understand the significance of NCX in excitation contraction (EC) coupling and pacemaker activity. Genetic alterations in the level of NCX have had unexpected effects that have informed the field about novel aspects of EC coupling in cardiac cells. The three proposed projects are as follows: 1. Sinoatrial Node Activity in Atrial-Specific NCX Knockout Mice. We have recently produced novel atrial-specific NCX knockout (KO) mice that live into adulthood, but exhibit profound bradycardia and sinaotrial node (SAN) dysfunction. In both intact ex vivo SAN preparations and in isolated SAN cells, we will study the underlying mechanism for these adaptations, including changes in cellular electrophysiology and subcellular Ca movements. These experiments will resolve fundamental disputes in cardiac pacemaker generation theory and may have an enormous impact on the field. 2. Adaptations of Atrial Excitation-Contraction Coupling to Genetically Altered Levels of NCX. We will test the hypothesis that critical adaptations in atrial Ca regulation and EC coupling occur when atrial NCX is knocked out. Since atrial myocytes lack the spatial constraints associated with transverse-tubules of ventricular cells, we can test the hypothesis that regulation of EC coupling by NCX depends on spatial gradients and cellular microdomains. These studies will provide us with important insights into regulation of contractility in the atrium that may have important therapeutic implications. 3. Adaptations of Ventricular Excitation-Contraction Coupling to Genetically Altered Levels of NCX. We have produced ventricular-specific NCX KO mice that survive into adulthood. Ventricular myocytes from these mice tolerate ablation of NCX by reducing Ca entry through L-type Ca channels, yet maintain contractility by increasing EC coupling gain without increasing sarcoplasmic reticulum Ca load. We have proposed that gain increases because lack of NCX elevates diadic cleft Ca, and that elevated cleft Ca increases EC coupling fidelity. This suggests that cleft Ca manipulation by NCX could be used as an alternative to -agonists as an inotropic strategy that avoids cellular Ca overload and its deleterious consequences. The experiments in this aim will fill critical gaps in our understanding of the mechanism through which NCX ablation raises EC coupling gain without provoking Ca overload and cell death. This knowledge is essential so that we can learn how to manipulate NCX and cleft Ca as therapeutic targets in patients with heart failure and ischemic cardiac dysfunction.

Public Health Relevance

This is a proposal to study the sodium-calcium exchanger (NCX), a major regulator of calcium in heart cells. Since calcium regulation by NCX fundamentally and critically affects the strength of heart muscle as well as the electrical pacemaker activity of the heart, it is essential to understand how NCX controls calcium in the heart. This has important implications for managing the altered calcium fluxes in heart failure (>1,000,000 hospitalizations in the U.S. per year), as well as sick sinus syndrome (that requires placement of >400,000 pacemakers in the U.S. annually).

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
2R01HL048509-19A1
Application #
8440105
Study Section
Electrical Signaling, Ion Transport, and Arrhythmias Study Section (ESTA)
Program Officer
Krull, Holly
Project Start
1992-09-30
Project End
2017-01-31
Budget Start
2013-02-01
Budget End
2014-01-31
Support Year
19
Fiscal Year
2013
Total Cost
$410,634
Indirect Cost
$149,500
Name
Cedars-Sinai Medical Center
Department
Type
DUNS #
075307785
City
Los Angeles
State
CA
Country
United States
Zip Code
90048
Ottolia, Michela; Torres, Natalia; Bridge, John H B et al. (2013) Na/Ca exchange and contraction of the heart. J Mol Cell Cardiol 61:28-33
Groenke, Sabine; Larson, Eric D; Alber, Sarah et al. (2013) Complete atrial-specific knockout of sodium-calcium exchange eliminates sinoatrial node pacemaker activity. PLoS One 8:e81633
Bai, Yan; Morgan, Eric E; Giovannucci, David R et al. (2013) Different roles of the cardiac Na+/Ca2+-exchanger in ouabain-induced inotropy, cell signaling, and hypertrophy. Am J Physiol Heart Circ Physiol 304:H427-35
Wang, JuFang; Gao, Erhe; Song, Jianliang et al. (2010) Phospholemman and beta-adrenergic stimulation in the heart. Am J Physiol Heart Circ Physiol 298:H807-15
Larbig, Robert; Torres, Natalia; Bridge, John H B et al. (2010) Activation of reverse Na+-Ca2+ exchange by the Na+ current augments the cardiac Ca2+ transient: evidence from NCX knockout mice. J Physiol 588:3267-76
Jordan, Maria C; Henderson, Scott A; Han, Tieyan et al. (2010) Myocardial function with reduced expression of the sodium-calcium exchanger. J Card Fail 16:786-96
Blaustein, Mordecai P; Zhang, Jin; Chen, Ling et al. (2009) The pump, the exchanger, and endogenous ouabain: signaling mechanisms that link salt retention to hypertension. Hypertension 53:291-8
Cavalli, Amy; Eghbali, Mansoureh; Minosyan, Tamara Y et al. (2007) Localization of sarcolemmal proteins to lipid rafts in the myocardium. Cell Calcium 42:313-22
Roos, Kenneth P; Jordan, Maria C; Fishbein, Michael C et al. (2007) Hypertrophy and heart failure in mice overexpressing the cardiac sodium-calcium exchanger. J Card Fail 13:318-29
Goldhaber, Joshua I; Henderson, Scott A; Reuter, Hannes et al. (2005) Effects of Na+-Ca2+ exchange expression on excitation-contraction coupling in genetically modified mice. Ann N Y Acad Sci 1047:122-6

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