Biomedical subjects

Howard A Rockman

Publications and source records attributed to Howard A Rockman.

At least 37 records · Page 2Linked to original sources

PubMed2005

QTL mapping in a mouse model of cardiomyopathy reveals an ancestral modifier allele affecting heart function and survival.

The progression from myocardial hypertrophy to heart failure is a complex process, involving genetic and environmental factors. Elucidating the genetic components contributing to heart failure has been difficult, largely because of the heterogeneity of human populations. We have employed a strategy to map genetic loci that modify the heart failure phenotype in a transgenic mouse model of cardiomyopathy caused by cardiac-specific overexpression of calsequestrin. Strain-specific differences in both cardiac function and survival are observed when the transgene is moved into different inbred mouse strains. We have previously reported linkage results from mapping in reciprocal backcrosses between C57/BL6 (BL6) and DBA/2J (DBA) and a backcross between DBA/AKR and AKR. Here we report the results of a genome-wide linkage scan in the reciprocal backcross between DBA/AKR and DBA. We identified one novel locus on Chromosome (Chr) 18 that affects heart function and a second on Chr 3 that shows significant linkage to both survival and heart function. Intriguingly, the Chr 3 allele of AKR shows a susceptibility effect on phenotype, whereas the overall effect of the AKR genetic background is protective. The Chr 3 locus also completely overlaps the Hrtfm2 locus, which was previously mapped in crosses between DBA and BL6. Mapping the same QTL in two different crosses allowed us to use ancestral haplotypes to narrow the candidate gene interval from 9 to 2 Mb. Identification of the genes at these QTLs in the mouse will provide novel candidate genes that can be evaluated for their role in human heart failure.

Alleles↗

PubMed2005

Prostacyclin protects against elevated blood pressure and cardiac fibrosis.

Specific inhibitors of COX-2 have been associated with increased risk for cardiovascular complications. These agents reduce prostacyclin (PGI2) without affecting production of thromboxane (Tx) A2. While this abnormal pattern of eicosanoid generation has been implicated in the development of vascular disease associated with COX-2 inhibition, its role in the development of hypertension, the most common cardiovascular complication associated with COX-2 inhibition, is not known. We report here that mice lacking the receptor for PGI2 (IPKOs) develop salt-sensitive hypertension, cardiac hypertrophy, and severe cardiac fibrosis. Coincidental deletion of the TxA2 (TP) receptor does not prevent the development of hypertension, but cardiac hypertrophy is ameliorated and fibrosis is prevented in IPTP double knockouts (DKOs). Thus, deletion of the IP receptor removes a constraint revealing adverse cardiovascular consequences of TxA2. Our data suggest that adjuvant therapy that blocks unrestrained Tx actions might protect against end-organ damage without affecting blood pressure in patients taking COX-2 inhibitors.

Aging↗

PubMed2005

Protein kinase activity of phosphoinositide 3-kinase regulates beta-adrenergic receptor endocytosis.

Phosphoinositide 3-kinase (PI(3)K) is a unique enzyme characterized by both lipid and protein kinase activities. Here, we demonstrate a requirement for the protein kinase activity of PI(3)K in agonist-dependent beta-adrenergic receptor (betaAR) internalization. Using PI(3)K mutants with either protein or lipid phosphorylation activity, we identify the cytoskeletal protein non-muscle tropomyosin as a substrate of PI(3)K, which is phosphorylated in a wortmannin-sensitive manner on residue Ser 61. A constitutively dephosphorylated (S61A) tropomyosin mutant blocks agonist-dependent betaAR internalization, whereas a tropomyosin mutant that mimics constitutive phosphorylation (S61D) complements the PI(3)K mutant, with only lipid phosphorylation activity reversing the defective betaAR internalization. Notably, knocking down endogenous tropomyosin expression using siRNAs that target different regions if tropomyosin resulted in complete inhibition of betaAR endocytosis, showing that non-muscle tropomyosin is essential for agonist-mediated receptor internalization. These studies demonstrate a previously unknown role for the protein phosphorylation activity of PI(3)K in betaAR internalization and identify non-muscle tropomyosin as a cellular substrate for protein kinase activity of PI(3)K.

Actins↗

PubMed2005

When 7 transmembrane receptors are not G protein-coupled receptors.

Classically, 7 transmembrane receptors transduce extracellular signals by coupling to heterotrimeric G proteins, although recent in vitro studies have clearly demonstrated that they can also signal via G protein-independent mechanisms. However, the physiologic consequences of this unconventional signaling, particularly in vivo, have not been explored. In this issue of the JCI, Zhai et al. demonstrate in vivo effects of G protein-independent signaling by the angiotensin II type 1 receptor (AT1R) (see the related article beginning on page 3045). In studies of the mouse heart, they compare the physiologic and biochemical consequences of transgenic cardiac-specific overexpression of a mutant AT1R incapable of G protein coupling with those of a wild-type receptor. Their results not only provide the first glimpse of the physiologic effects of this newly appreciated mode of signaling but also provide important and previously unappreciated clues as to the underlying molecular mechanisms.

Animals↗

PubMed2005

Methods for the detection of altered beta-adrenergic receptor signaling pathways in hypertrophied hearts.

Beta-adrenergic receptor signaling, desensitization, and downregualtion are fundamental mechanisms that contribute to both normal and altered myocardial function. The development of pharmacological and biochemical assays has provided the ability to measure alterations both in adrenergic receptor density and the subsequent coupling of adrenergic receptors downstream effectors, namely, adenylyl cyclase. Furthermore, transthoracic echocardiography of the murine heart has provided insight into changes in cardiac physiology that accompany altered adrenergic receptor signaling. The protocols described within this chapter provide the means to quantify beta-adrenergic density, measure adenylyl cyclase activity, and evaluate cardiac hypertrophy to better understand the mechanisms responsible for cardiac hypertrophy and heart failure.

Adenylyl Cyclases↗

PubMed2004

Muscle-specific RING finger 1 is a bona fide ubiquitin ligase that degrades cardiac troponin I.

Muscle-specific RING finger protein 1 (MuRF1) is a sarcomere-associated protein that is restricted to cardiac and skeletal muscle. In skeletal muscle, MuRF1 is up-regulated by conditions that provoke atrophy, but its function in the heart is not known. The presence of a RING finger in MuRF1 raises the possibility that it is a component of the ubiquitin-proteasome system of protein degradation. We performed a yeast two-hybrid screen to search for interaction partners of MuRF1 in the heart that might be targets of its putative ubiquitin ligase activity. This screen identified troponin I as a MuRF1 partner protein. MuRF1 and troponin I were found to associate both in vitro and in vivo in cultured cardiomyocytes. MuRF1 reduced steady-state troponin I levels when coexpressed in COS-7 cells and increased degradation of endogenous troponin I protein in cardiomyocytes. The degradation of troponin I in cardiomyocytes was associated with the accumulation of ubiquitylated intermediates of troponin I and was proteasome-dependent. In vitro, MuRF1 functioned as a ubiquitin ligase to catalyze ubiquitylation of troponin I through a RING finger-dependent mechanism. In isolated cardiomyocytes, MuRF1 reduced indices of contractility. In cardiomyocytes, these processes may determine the balance between hypertrophic and antihypertrophic signals and the regulation of myocyte contractile responses in the setting of heart failure.

Animals↗

PubMed2004

cTnT1, a cardiac troponin T isoform, decreases myofilament tension and affects the left ventricular pressure waveform.

Four isoforms of cardiac troponin T (cTnT), a protein essential for calcium-dependent myocardial force development, are expressed in the human; they differ in charge and length. Their expression is regulated developmentally and is affected by disease states. Human cTnT (hcTnT) isoform effects have been examined in reconstituted myofilaments. In this study, we evaluated the modulatory effects of overexpressing one cTnT isoform on in vitro and in vivo myocardial function. A hcTnT isoform, hcTnT(1), expressed during development and in heart disease but not in the normal adult heart, was expressed in transgenic (TG) mice (1-30% of total cTnT). Maximal active tension measured in skinned myocardium decreased as a function of relative hcTnT(1) expression. The pCa at half-maximal force development, Hill coefficient, and rate of redevelopment of force did not change significantly with hcTnT(1) expression. In vivo maximum rates of rise and fall of left ventricular pressure decreased, and the half-time of isovolumic relaxation increased, with hcTnT(1) expression. Substituting total cTnT charge for hcTnT(1) expression resulted in similar conclusions. Morphometric analysis and electron microscopy revealed no differences between wild-type (non-TG) and TG myocardium. No differences in isoform expression of tropomyosin, myosin heavy chain, essential and regulatory myosin light chains (MLC), TnI, or in posttranslational modifications of mouse cTnT, cTnI, or regulatory MLC were observed. These results support the hypothesis that cTnT isoform amino-terminal differences affect myofilament function and suggest that hcTnT(1) expression levels present during human development and in human heart disease can affect in vivo ventricular function.

Actin Cytoskeleton↗

PubMed2004

Overexpression of mitogen-activated protein kinase kinase 6 in the heart improves functional recovery from ischemia in vitro and protects against myocardial infarction in vivo.

The mitogen-activated protein kinases (MAPK) have been the subject of many studies to identify signaling pathways that promote cell survival or death. In cultured cardiac myocytes, p38 MAPK promotes cell survival or death depending on whether it is activated by mitogen-activated protein kinase kinase 6 (MKK6) or MKK3, respectively. The objectives of the current study were to examine the effects of MKK6-mediated p38 activation in the heart in vivo. Accordingly, we generated transgenic (TG) mice that overexpress wild type MKK6 in a cardiac-restricted manner. Although p38 was about 17-fold more active in TG than non-transgenic (NTG) mouse hearts, TG mouse hearts were morphologically and functionally similar to those of NTG littermates. However, upon transient ischemia followed by reperfusion, the MKK6 TG mouse hearts exhibited significantly better functional recovery and less injury than NTG mouse hearts. Because MKK6 increases levels of the protective small heat shock protein, alpha B-crystallin (alpha BC), in cultured cardiac myocytes, we examined alpha BC levels in the mouse hearts. The level of alpha BC was 2-fold higher in MKK6 TG than NTG mouse hearts. Moreover, ischemia followed by reperfusion induced a 6.4-fold increase in alpha BC levels in the mitochondrial fractions of TG mouse hearts but no increase in alpha BC levels in any of the other fractions analyzed. These alterations in alpha BC expression and localization suggest possible mechanisms of cardioprotection in MKK6 TG mouse hearts.

Animals↗

PubMed2004

Estrogen receptor-beta mediates male-female differences in the development of pressure overload hypertrophy.

The goal of this study was to determine the role of estrogen receptor subtypes in the development of pressure overload hypertrophy in mice. Epidemiological studies have suggested gender differences in the development of hypertrophy and heart disease, but the mechanism and the role of estrogen receptor subtypes are not established. We performed transverse aortic constriction (TAC) and sham operations in male and female wild-type (WT) mice and mice lacking functional estrogen receptor-alpha [alpha-estrogen receptor knockout (alpha-ERKO)] and mice lacking estrogen receptor-beta (beta-ERKO). Body, heart, and lung weights were measured 2 wk postsurgery. WT male mice subjected to TAC showed a 64% increase in the heart weight-to-body weight ratio (HW/BW) compared with sham, and WT males have increased lung weight at 2 wk. WT female mice subjected to TAC showed a 31% increase in HW/BW compared with sham, which was significantly less than their male counterparts and with no evidence of heart failure. alpha-ERKO females developed HW/BW nearly identical to that seen in WT littermate females in response to TAC, indicating that estrogen receptor-alpha is not essential for the attenuation of hypertrophy observed in WT females. In contrast, beta-ERKO females responded to TAC with a significantly greater increase in HW/BW than WT littermate females. beta-ERKO females have lower expression of lipoprotein lipase at baseline than WT or alpha-ERKO females. These data suggest an important role for estrogen receptor-beta in attenuating the hypertrophic response to pressure overload in females.

Animals↗

PubMed2004

Network integration of the adrenergic system in cardiac hypertrophy.

Adrenergic receptors play a pivotal role in regulating cardiac function in response to a constantly changing environment. Altered alpha and beta adrenergic receptor signaling in vivo is associated with cardiac hypertrophy and failure. This review focuses on the different roles of adrenergic receptors in regulating cardiac function under normal and pathological conditions. Understanding the signaling mechanisms of these receptors in the context of the heart is likely to provide a better therapeutic approach towards treatment of heart failure.

Animals↗

PubMed2004

Enhanced postischemic functional recovery in CYP2J2 transgenic hearts involves mitochondrial ATP-sensitive K+ channels and p42/p44 MAPK pathway.

Human CYP2J2 is abundant in heart and active in the biosynthesis of epoxyeicosatrienoic acids (EETs); however, the functional role of this P450 and its eicosanoid products in the heart remains unknown. Transgenic mice with cardiomyocyte-specific overexpression of CYP2J2 were generated. CYP2J2 transgenic (Tr) mice have normal heart anatomy and basal contractile function. CYP2J2 Tr hearts have improved recovery of left ventricular developed pressure (LVDP) compared with wild-type (WT) hearts after 20 minutes ischemia and 40 minutes reperfusion. Perfusion with the selective P450 epoxygenase inhibitor N-methylsulphonyl-6-(2-proparglyloxyphenyl)hexanamide (MS-PPOH) for 20 minutes before ischemia results in reduced postischemic LVDP recovery in WT hearts and abolishes the improved postischemic LVDP recovery in CYP2J2 Tr hearts. Perfusion with the ATP-sensitive K(+) channel (K(ATP)) inhibitor glibenclamide (GLIB) or the mitochondrial K(ATP) (mitoK(ATP)) inhibitor 5-hydroxydecanoate (5-HD) for 20 minutes before ischemia abolishes the cardioprotective effects of CYP2J2 overexpression. Flavoprotein fluorescence, a marker of mitoK(ATP) activity, is higher in cardiomyocytes from CYP2J2 Tr versus WT mice. Moreover, CYP2J2-derived EETs (1 to 5 micromol/L) increase flavoprotein fluorescence in WT cardiomyocytes. CYP2J2 Tr mice exhibit increased expression of phospho-p42/p44 mitogen-activated protein kinase (MAPK) after ischemia, and addition of the p42/p44 MAPK kinase (MEK) inhibitor PD98059 during reperfusion abolishes the cardioprotective effects of CYP2J2 overexpression. Together, these data suggest that CYP2J2-derived metabolites are cardioprotective after ischemia, and the mechanism for this cardioprotection involves activation of mitoK(ATP) and p42/p44 MAPK.

Animals↗

PubMed2004

G protein-coupled receptor internalization signaling is required for cardioprotection in ischemic preconditioning.

The present study is designed to explore the role of G protein-coupled receptors (GPCRs) in the protection afforded by ischemic preconditioning (PC). We used TG mice with cardiac-specific overexpression of a Gbetagamma-sequestering peptide, betaARKct (TG betaARKct mice), to test whether the protection of PC is Gbetagamma-dependent. To test the role of G(i) protein, we used wild-type mice pretreated with the G(i) inhibitor pertussis toxin. Recovery of left ventricular developed pressure and infarct size were measured as indices of protection. PC induced protection in wild-type mice, but this protection was blocked by pertussis toxin treatment and was also blocked in TG betaARKct mice. To determine the mechanism of Gbetagamma-induced protection in PC, we investigated one of the downstream targets of Gbetagamma, the PI3K/p70S6K pathway. PC-induced phosphorylation of p70S6K was not blocked in TG betaARKct hearts; therefore, we investigated other targets of Gbetagamma. Recent studies suggest a role for Gbetagamma in GPCR internalization. We found that betaARKct, a specific PI3K inhibitor wortmannin, and bafilomycin A1, which all block receptor recycling, all blocked the protective effect of PC. To additionally test whether PI3K is involved in PC-activated receptor internalization and endosomal signaling, we used TG mice with cardiac-specific overexpression of a catalytically inactive mutant PI3Kgamma, which disrupts the recruitment of functional PI3K to agonist-activated GPCRs in vivo. We found that the catalytically inactive mutant of PI3Kgamma blocks the protection of PC. In summary, these data suggest the novel finding that the cardioprotective effect of PC requires receptor internalization.

Androstadienes↗

PubMed2003

Differential myocardial gene expression in the development and rescue of murine heart failure.

Numerous murine models of heart failure (HF) have been described, many of which develop progressive deterioration of cardiac function. We have recently demonstrated that several of these can be "rescued" or prevented by transgenic cardiac expression of a peptide inhibitor of the beta-adrenergic receptor kinase (betaARKct). To uncover genomic changes associated with cardiomyopathy and/or its phenotypic rescue by the betaARKct, oligonucleotide microarray analysis of left ventricular (LV) gene expression was performed in a total of 53 samples, including 12 each of Normal, HF, and Rescue. Multiple statistical analyses demonstrated significant differences between all groups and further demonstrated that betaARKct Rescue returned gene expression toward that of Normal. In our statistical analyses, we found that the HF phenotype is blindly predictable based solely on gene expression profile. To investigate the progression of HF, LV gene expression was determined in young mice with mildly diminished cardiac function and in older mice with severely impaired cardiac function. Interestingly, mild and advanced HF mice shared similar gene expression profiles, and importantly, the mild HF mice were predicted as having a HF phenotype when blindly subjected to our predictive model described above. These data not only validate our predictive model but further demonstrate that, in these mice, the HF gene expression profile appears to already be set in the early stages of HF progression. Thus we have identified methodologies that have the potential to be used for predictive genomic profiling of cardiac phenotype, including cardiovascular disease.

Animals↗

PubMed2003

Multiple quantitative trait loci modify the heart failure phenotype in murine cardiomyopathy.

The variability in outcome of heart failure patients depends on a number of factors including differences in their genetic background. To identify novel genes that modify the human heart failure phenotype, we used a strategy of quantitative trait locus (QTL) mapping in an experimental mouse model of dilated cardiomyopathy induced by cardiac-specific overexpression of calsequestrin and characterized by a strong strain-specific variability in the phenotype. We identified two novel QTLs, Hrtfm3 (heart failure modifier 3) on chromosome (Chr) 4 and Hrtfm4 on Chr 18, significantly linked to survival with likelihood ratio statistics (LRS) of 19.9 and 23.6 respectively (corresponding to LOD scores of 4.3 and 5.1). Two other QTLs, Hrtfm5 on Chr 2 and Hrtfm6 on Chr 13, were significantly linked to cardiac function as measured by echocardiographic fractional shortening (LRS 22.1 and 15.2 respectively, LOD score 4.8 and 3.3) and left ventricular end-diastolic diameter (LRS 23.5 and 18.8, LOD score 5.1 and 4.1). Importantly, Hrtfm5 was not significantly linked to survival. A significant interaction was found between Hrtfm4 and two other QTLs (Hrtfm6 and a QTL near to the marker D19Mit88) for fractional shortening with a LRS of 34.6 and 26.5 respectively (LOD score 7.5 and 5.8). These data show that the effect of genetic background on murine heart failure is complex and result from the action of several loci that differentially modify the cardiac phenotype. The identification of these novel modifier genes will serve as strong candidates for the discovery of modifiers in human heart failure.

Animals↗

PubMed2003

Dual inhibition of beta-adrenergic and angiotensin II receptors by a single antagonist: a functional role for receptor-receptor interaction in vivo.

BACKGROUND: Although the renin-angiotensin and the beta-adrenergic systems are interrelated, a direct interaction between beta-adrenergic receptors (betaARs) and angiotensin II type 1 receptors (AT1Rs) has not been identified. METHODS AND RESULTS: Here, we provide evidence for a functional and physiological interaction between 2 G protein-coupled receptors: the betaAR and the AT1R. Selective blockade of betaARs in mouse cardiomyocytes inhibits angiotensin-induced contractility with an IC50 that is similar to its inhibition of isoproterenol-mediated contractility. Furthermore, administration of the angiotensin receptor blocker valsartan to intact mice results in a significant reduction in the maximal response to catecholamine-induced elevation of heart rate. The mechanism for this transinhibitory effect of beta-blockers and angiotensin receptor blockers is through receptor-G protein uncoupling; ie, beta-blockers interfere with AT1R-Gq coupling, and valsartan interferes with betaAR-Gs coupling. Finally, we demonstrate that AT1Rs and betaARs form constitutive complexes that are not affected by ligand stimulation. As a result of these interactions, a single receptor antagonist effectively blocks downstream signaling and trafficking of both receptors simultaneously. CONCLUSIONS: We show that direct interactions between betaARs and AT1Rs may have profound consequences on the overall response to drugs that antagonize these receptors.

Adrenergic beta-Antagonists↗

PubMed2003

Cardiac hypertrophy and altered beta-adrenergic signaling in transgenic mice that express the amino terminus of beta-ARK1.

The G protein-coupled receptor (GPCR) kinase beta-adrenergic receptor (beta-AR) kinase-1 (beta-ARK1) is elevated during heart failure; however, its role is not fully understood. Beta-ARK1 contains several domains that are capable of protein-protein interactions that may play critical roles in the regulation of GPCR signaling. In this study, we developed a novel line of transgenic mice that express an amino-terminal peptide of beta-ARK1 that is comprised of amino acid residues 50-145 (beta-ARKnt) in the heart to determine whether this domain has any functional significance in vivo. Surprisingly, the beta-ARKnt transgenic mice presented with cardiac hypertrophy. Our data suggest that the phenotype was driven via an enhanced beta-AR system, as beta-ARKnt mice had elevated cardiac beta-AR density. Moreover, administration of a beta-AR antagonist reversed hypertrophy in these mice. Interestingly, signaling through the beta-AR in response to agonist stimulation was not enhanced in these mice. Thus the amino terminus of beta-ARK1 appears to be critical for normal beta-AR regulation in vivo, which further supports the hypothesis that beta-ARK1 plays a key role in normal and compromised cardiac GPCR signaling.

Animals↗

PubMed2003

Protein kinase A and G protein-coupled receptor kinase phosphorylation mediates beta-1 adrenergic receptor endocytosis through different pathways.

Agonist-induced phosphorylation of beta-adrenergic receptors (beta ARs) by G protein-coupled receptor kinases (GRKs) results in their desensitization followed by internalization. Whether protein kinase A (PKA)-mediated phosphorylation of beta ARs, particularly the beta 1AR subtype, can also trigger internalization is currently not known. To test this, we cloned the mouse wild type beta 1AR (WT beta 1AR) and created 3 mutants lacking, respectively: the putative PKA phosphorylation sites (PKA-beta 1AR), the putative GRK phosphorylation sites (GRK-beta 1AR), and both sets of phosphorylation sites (PKA-/GRK-beta 1AR). Following agonist stimulation, both PKA-beta 1AR and GRK-beta 1AR mutants showed comparable increases in phosphorylation and desensitization. Saturating concentrations of agonist induced only 50% internalization of either mutant compared with wild type, suggesting that both PKA and GRK phosphorylation of the receptor contributed to receptor sequestration in an additive manner. Moreover, in contrast to the WT beta 1AR and PKA-beta 1AR, sequestration of the GRK-beta 1AR and PKA-/GRK-beta 1AR was independent of beta-arrestin recruitment. Importantly, clathrin inhibitors abolished agonist-dependent internalization for both the WT beta 1AR and PKA-beta 1AR, whereas caveolae inhibitors prevented internalization only of the GRK-beta 1AR mutant. Taken together, these data demonstrate that: 1) PKA-mediated phosphorylation can trigger agonist-induced internalization of the beta 1AR and 2) the pathway selected for beta 1AR internalization is primarily determined by the kinase that phosphorylates the receptor, i.e. PKA-mediated phosphorylation directs internalization via a caveolae pathway, whereas GRK-mediated phosphorylation directs it through clathrin-coated pits.

Animals↗

PubMed2003

Transgenic overexpression of the Ca2+-binding protein S100A1 in the heart leads to increased in vivo myocardial contractile performance.

S100A1, a Ca2+-sensing protein of the EF-hand family, is most highly expressed in myocardial tissue, and cardiac S100A1 overexpression in vitro has been shown to enhance myocyte contractile properties. To study the physiological consequences of S100A1 in vivo, transgenic mice were developed with cardiac-restricted overexpression of S100A1. Characterization of two independent transgenic mouse lines with approximately 4-fold overexpression of S100A1 in the myocardium revealed a marked augmentation of in vivo basal cardiac function that remained elevated after beta-adrenergic receptor stimulation. Contractile function and Ca2+ handling properties were increased in ventricular cardiomyocytes isolated from S100A1 transgenic mice. Enhanced cellular Ca2+ cycling by S100A1 was associated both with increased sarcoplasmic reticulum Ca2+ content and enhanced sarcoplasmic reticulum Ca2+-induced Ca2+ release, and S100A1 was shown to associate with the cardiac ryanodine receptor. No alterations in beta-adrenergic signal transduction or major cardiac Ca2+-cycling proteins occurred, and there were no signs of hypertrophy with chronic cardiac S100A1 overexpression. Our findings suggest that S100A1 plays an important in vivo role in the regulation of cardiac function perhaps through interacting with the ryanodine receptor. Because S100A1 protein expression is down-regulated in heart failure, increasing S100A1 expression in the heart may represent a novel means to augment contractility.

Adrenergic beta-Agonists↗