Apela improves cardiac and renal function in mice with acute myocardial infarction

Apela was recently identified as a new ligand of the apelin peptide jejunum (APJ) receptor. The purpose of this study was to investigate the role of apela in post‐myocardial infarction (post‐MI) recovery from cardiorenal damage. A murine MI model was established, and apela was then infused subcutaneously for two weeks. Echocardiographs were performed before and after infarction at the indicated times. Renal function was evaluated by serum and urine biochemistry. Immunohistochemistry of heart and kidney tissue was performed by in situ terminal deoxynucleotidyl transferase‐mediated dUPT nick end‐labelling reaction. Compared to the control group (MI/vehicle), the average value of the left ventricular ejection fraction in apela‐treated mice increased by 32% and 39% at 2‐ and 4‐week post‐MI, respectively. The mean levels of serum blood urea nitrogen,creatinine, N‐terminal pro‐brain natriuretic peptide and 24‐hour urine protein were significantly decreased at 4‐week post‐MI in apela‐treated mice relative to that of control animals. At the cellular level, we found that apela treatment significantly reduced myocardial fibrosis and cellular apoptosis in heart and kidney tissue. These data suggest that apela improves cardiac and renal function in mice with acute MI. The peptide may be potential therapeutic agent for heart failure.     

Inhibition of cyclooxygenase-2 improves cardiac function in myocardial infarction

Induction of cyclooxygenase-2 (COX-2) in ischemic myocardium is thought to increase the production of proinflammatory prostanoids and contribute significantly to the ischemic inflammation. Left ventricular myocardial infarction (MI) was created by ligating the left coronary artery in Lewis rats. Hemodynamic measurements at 4 weeks showed better cardiac function in the group treated with a selective COX-2 inhibitor (DFU; 5 mg/kg/day) for 2 weeks after induction of MI compared to the vehicle treated group. These results suggest that induction of COX-2 contributes to myocardial dysfunction, and that selective inhibition of COX-2 could constitute an important therapeutic target for the treatment of MI.     

Fluorofenidone attenuates renal interstitial fibrosis in the rat model of obstructive nephropathy

Fluorofenidone (FD) is a novel pyridone agent with significant antifibrotic effects in vitro. The purpose of this study is to investigate the effects of FD on renal interstitial fibrosis in rats with obstructive nephropathy caused by unilateral ureteral obstruction (UUO). With pirfenidone (PD, 500 mg/kg/day) and enalapril (10 mg/kg/day) as the positive treatment controls, the rats in different experimental groups were administered with FD (500 mg/kg/day) from day 4 to day 14 after UUO. The tubulointerstitial injury, interstitial collagen deposition, and expression of type I and type III collagen, transforming growth factor-β(1) (TGF-β(1)), connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF), α-smooth muscle actin (α-SMA), and tissue inhibitor of metalloproteinase-1 (TIMP-1) were assessed. FD treatment significantly attenuated the prominently increased scores of tubulointerstitial injury, interstitial collagen deposition, and protein expression of type I and type III collagen in ureter-obstructed kidneys, respectively. As compared with untreated rats, FD also significantly reduced the expression of α-SMA, TGF-β(1), CTGF, PDGF, and inhibitor of TIMP-1 in the obstructed kidneys. Fluorofenidone attenuates renal interstitial fibrosis in the rat model of obstructive nephropathy through its regulation on fibrogenic growth factors, tubular cell transdifferentiation, and extracellular matrix.     

Erythropoietin attenuates cardiac dysfunction by increasing myocardial angiogenesis and inhibiting interstitial fibrosis in diabetic rats

ABSTRACT: BACKGROUND: Recent studies revealed that erythropoietin (EPO) has tissue-protective effects in the heart by increasing vascular endothelial growth factor (VEGF) expression and attenuating myocardial fibrosis in ischemia models. In this study, we investigated the effect of EPO on ventricular remodeling and blood vessel growth in diabetic rats. METHODS: Male SD rats were randomly divided into 3 groups: control rats, streptozotocin (STZ)-induced diabetic rats, and diabetic rats treated with 1000 U/kg EPO by subcutaneous injection once per week. Twelve weeks later, echocardiography was conducted, and blood samples were collected for counting of peripheral blood endothelial progenitor cells (EPCs). Myocardial tissues were collected, quantitative real-time PCR (RT-PCR) was used to detect the mRNA expression of VEGF and EPO-receptor (EPOR), and Western blotting was used to detect the protein expression of VEGF and EPOR. VEGF, EPOR, transforming growth factor beta (TGF-beta), and CD31 levels in the myocardium were determined by immunohistochemistry. To detect cardiac hypertrophy, immunohistochemistry of collagen type , collagen type , and Picrosirius Red staining were performed, and cardiomyocyte cross-sectional area was measured. RESULTS: After 12 weeks STZ injection, blood glucose increased significantly and remained consistently elevated. EPO treatment significantly improved cardiac contractility and reduced diastolic dysfunction. Rats receiving the EPO injection showed a significant increase in circulating EPCs (27.85+/-3.43%, P < 0.01) compared with diabetic untreated animals. EPO injection significantly increased capillary density as well as EPOR and VEGF expression in left ventricular myocardial tissue from diabetic rats. Moreover, EPO inhibited interstitial collagen deposition and reduced TGF-beta expression. CONCLUSIONS: Treatment with EPO protects cardiac tissue in diabetic animals by increasing VEGF and EPOR expression levels, leading to improved revascularization and the inhibition of cardiac fibrosis. Key words: erythropoietin; vascular endothelial growth factor; diabetes mellitus; endothelial progenitor cell; myocardial interstitial fibrosis; transforming growth factor beta.     

Intracardiac injection of erythropoietin induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Erythropoietin (EPO) protects the myocardium from ischaemic injury and promotes beneficial remodelling. We assessed the therapeutic efficacy of intracardiac EPO injection and EPO-mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, EPO (3000 U/kg) or saline was delivered by intracardiac injection. Compared to myocardial infarction control group (MIC), EPO significantly improved left ventricular function ( n = 11–14, P < 0.05) and decreased right ventricular wall stress ( n = 8, P < 0.05) assessed by pressure-volume loops after 6 weeks. MI-EPO hearts exhibited smaller infarction size (20.1 ± 1.1% versus 27.8 ± 1.2%; n = 6–8, P < 0.001) and greater capillary density (338.5 ± 14.7 versus 259.8 ± 9.2 vessels per mm; n = 6–8, P < 0.001) than MIC hearts. Direct EPO injection reduced post-MI myocardial apoptosis by approximately 41% (0.27 ± 0.03% versus 0.42 ± 0.03%; n = 6, P = 0.005). The chemoattractant SDF-1 was up-regulated significantly assessed by quantitative realtime PCR and immunohistology. c-Kit⁺ and CD34⁺ stem cells were significantly more numerous in MI-EPO than in MIC at 24 hrs in peripheral blood ( n = 7, P < 0.05) and 48 hrs in the infarcted hearts ( n = 6, P < 0.001). Further, the mRNAs of Akt, eNOS and EPO receptor were significantly enhanced in MI-EPO hearts ( n = 7, P < 0.05). Intracardiac EPO injection restores myocardial functions following MI, which may attribute to the improved early recruitment of c-Kit⁺ and CD34⁺ stem cells via the enhanced expression of chemoattractant SDF-1.     

Intracardiac injection of matrigel induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Matrigel promotes angiogenesis in the myocardium from ischemic injury and prevents remodelling of the left ventricle. We assessed the therapeutic efficacy of intracardiac matrigel injection and matrigel‐mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, matrigel (250 μl) or phosphate‐buffered solution (PBS) was delivered by intracardiac injection. Compared to the MI control group (MI‐PBS), matrigel significantly improved left ventricular function (n= 11, P < 0.05) assessed by pressure–volume loops after 4 weeks. There is no significant difference in infarct size between MI‐matrigel (MI‐M; 21.48 ± 1.49%, n= 10) and MI‐PBS hearts (20.98 ± 1.25%, n= 10). The infarct wall thickness of left ventricle is significantly higher (P < 0.01) in MI‐M (0.72 ± 0.02 mm, n= 10) compared with MI‐PBS (0.62 ± 0.02 mm, n= 10). MI‐M hearts exhibited higher capillary density (border 130.8 ± 4.7 versus 115.4 ± 6.0, P < 0.05; vessels per high‐power field [HPF; 400×], n= 6) than MI‐PBS hearts. c‐Kit⁺ stem cells (38.3 ± 5.3 versus 25.7 ± 1.5 c‐Kit⁺ cells per HPF [630×], n= 5, P < 0.05) and CD34⁺ cells (13.0 ± 1.51 versus 5.6 ± 0.68 CD34⁺ cells per HPF [630×], n= 5, P < 0.01) were significantly more numerous in MI‐M than in MI‐PBS in the infarcted hearts (n= 5, P < 0.05). Intracardiac matrigel injection restores myocardial functions following MI, which may attribute to the improved recruitment of CD34⁺ and c‐Kit⁺ stem cells.     

Human mesenchymal stem cell-conditioned medium improves cardiac function following myocardial infarction

Recent studies suggest that the therapeutic effects of stem cell transplantation following myocardial infarction (MI) are mediated by paracrine factors. One of the main goals in the treatment of ischemic heart disease is to stimulate vascular repair mechanisms. Here, we sought to explore the therapeutic angiogenic potential of mesenchymal stem cell (MSC) secretions. Human MSC secretions were collected as conditioned medium (MSC-CM) using a clinically compliant protocol. Based on proteomic and pathway analysis of MSC-CM, an in vitro assay of HUVEC spheroids was performed identifying the angiogenic properties of MSC-CM. Subsequently, pigs were subjected to surgical left circumflex coronary artery ligation and randomized to intravenous MSC-CM treatment or non-CM (NCM) treatment for 7 days. Three weeks after MI, myocardial capillary density was higher in pigs treated with MSC-CM (645 ± 114 vs 981 ± 55 capillaries/mm(2); P = 0.021), which was accompanied by reduced myocardial infarct size and preserved systolic and diastolic performance. Intravenous MSC-CM treatment after myocardial infarction increases capillary density and preserves cardiac function, probably by increasing myocardial perfusion.     

Inhibition of cyclooxygenase-2 improves cardiac function after myocardial infarction in the mouse

Cyclooxygenase (COX)-2 is expressed in the heart in animal models of ischemic injury. Recent studies have suggested that COX-2 products are involved in inflammatory cell infiltration and fibroblast proliferation in the heart. Using a mouse model, we questioned whether 1). myocardial infarction (MI) in vivo induces COX-2 expression chronically, and 2). COX-2 inhibition reduces collagen content and improves cardiac function in mice with MI. MI was produced by ligation of the left anterior descending coronary artery in mice. Two days later, mice were treated with 3 mg/kg NS-398, a selective COX-2 inhibitor, or vehicle in drinking water for 2 wk. After the treatment period, mice were subjected to two-dimensional M-mode echocardiography to determine cardiac function. Hearts were then analyzed for determination of infarct size, interstitial collagen content, brain natriuretic peptide (BNP) mRNA, myocyte cross-sectional area, and immunohistochemical staining for transforming growth factor (TGF)-beta and COX-2. COX-2 protein, detected by immunohistochemistry, was increased in MI versus sham hearts. MI resulted in increased left ventricular systolic and diastolic dimension and decreased ejection fraction, fractional shortening, and cardiac output. NS-398 treatment partly reversed these detrimental changes. Myocyte cross-sectional area, a measure of hypertrophy, was decreased by 30% in the NS-398 versus vehicle group, but there was no effect on BNP mRNA. The interstitial collagen fraction increased from 5.4 +/- 0.4% in sham hearts to 10.4 +/- 0.9% in MI hearts and was decreased to 7.9 +/- 0.6% in NS-398-treated hearts. A second COX-2 inhibitor, rofecoxib (MK-0966), also decreased myocyte cross-sectional area and interstitial collagen fraction. TGF-beta, a key regulator of collagen synthesis, was increased in MI hearts. NS-398 treatment reduced TGF-beta immunostaining by 40%. NS-398 treatment had no effect on infarct size. These results suggest that COX-2 products contribute to cardiac remodeling and functional deficits after MI. Thus selected inhibition of COX-2 may be a therapeutic target for reducing myocyte damage after MI.     

Overexpression of apolipoprotein-B improves cardiac function and increases survival in mice with myocardial infarction

Background

The heart produces apolipoprotein-B containing lipoproteins (apoB) whose function is not well understood. The aim of this study was to evaluate importance of myocardial apoB for cardiac function, structure and survival in myocardial infarction (MI) and heart failure (HF).

Methods and results

MI was induced in mice (n = 137) and myocardial apoB content was measured at 30 min, 3, 6, 24, 48, 120 h and 8 weeks post-MI. Transgenic mice overexpressing apoB (n = 27) and genetically matched controls (n = 27) were used to study the effects of myocardial apoB on cardiac function, remodeling, arrhythmias and survival after MI. Echocardiography was performed at rest and stress conditions at baseline, 2, 4 and 6 week post-MI and cumulative survival rate was registered. The myocardial apoB content increased both in the injured and the remote myocardium (p < 0.05) in response to ischemic injury. ApoB mice had 2-fold higher survival rate (p < 0.05) and better systolic function (p < 0.05) post-MI.

Conclusion

Overexpression of apoB in the heart increases survival and improves cardiac function after acute MI. Myocardial apoB may be an important cardioprotective system in settings such as myocardial ischemia and HF.     

Intravenous administration of mesenchymal stem cells improves cardiac function in rats with acute myocardial infarction through angiogenesis and myogenesis

Mesenchymal stem cells (MSCs) are pluripotent cells that differentiate into a variety of cells, including cardiomyocytes and endothelial cells. However, little information is available regarding the therapeutic potency of systemically delivered MSCs for myocardial infarction. Accordingly, we investigated whether intravenously transplanted MSCs induce angiogenesis and myogenesis and improve cardiac function in rats with acute myocardial infarction. MSCs were isolated from bone marrow aspirates of isogenic adult rats and expanded ex vivo. At 3 h after coronary ligation, 5 x 10(6) MSCs (MSC group, n=12) or vehicle (control group, n=12) was intravenously administered to Lewis rats. Transplanted MSCs were preferentially attracted to the infarcted, but not the noninfarcted, myocardium. The engrafted MSCs were positive for cardiac markers: desmin, cardiac troponin T, and connexin43. On the other hand, some of the transplanted MSCs were positive for von Willebrand factor and formed vascular structures. Capillary density was markedly increased after MSC transplantation. Cardiac infarct size was significantly smaller in the MSC than in the control group (24 +/- 2 vs. 33 +/- 2%, P <0.05). MSC transplantation decreased left ventricular end-diastolic pressure and increased left ventricular maximum dP/dt (both P <0.05 vs. control). These results suggest that intravenous administration of MSCs improves cardiac function after acute myocardial infarction through enhancement of angiogenesis and myogenesis in the ischemic myocardium.     

Selective inhibition of p38alpha MAPK improves cardiac function and reduces myocardial apoptosis in rat model of myocardial injury

p38 MAPK is activated during heart diseases that might associate with myocardial damage and deterioration of cardiac function. In a rat model of myocardial injury, we have investigated cardioprotective effects of the inhibition of p38 MAPK using a novel, orally available p38alpha MAPK inhibitor. Rats were treated with N(omega)-nitro-l-arginine methyl ester (l-NAME, 40 mg.kg(-1).day(-1)) in drinking water plus 1% salt for 14 days and ANG II (0.5 mg.kg(-1).day(-1)) for 3 days. A selective p38alpha MAPK inhibitor, SD-282 (60 mg/kg), was administrated orally, twice a day for 4 days, starting 1 day before ANG II administration. The cardioprotective effects of p38alpha MAPK inhibition were evaluated by improvement of cardiac function, reduction of inflammatory cell infiltration, and cardiomyocyte apoptosis. SD-282 significantly improved cardiac function indicated by increasing stroke volume, cardiac output, ejection fraction, and stroke work and significantly decreasing arterial elastance. SD-282 also significantly reduced macrophage infiltration as judged by reduction of a specific marker, ED-1-positive staining cells (P < 0.05) in the myocardium. Furthermore, cardiomyocyte apoptosis as indicated by caspase-3 immunohistochemical staining was abolished by SD-282, and this effect may contribute to the reduction of myocardial damage evaluated by imaging analysis (P < 0.05 in both cases). Data suggest that p38alpha MAPK may play a critical role in the pathogenesis of cardiac dysfunction. Inhibition of p38alpha MAPK may be used as a novel cardioprotective strategy in attenuation of inflammatory response and deterioration of cardiac function that occurs in acute cardiovascular disease such as myocardial infarction.     

Metformin improves cardiac function in a nondiabetic rat model of post-MI heart failure

Metformin is the first choice drug for the treatment of patients with diabetes, but its use is debated in patients with advanced cardiorenal disease. Epidemiological data suggest that metformin may reduce cardiac events, in patients both with and without heart failure. Experimental evidence suggests that metformin reduces cardiac ischemia-reperfusion injury. It is unknown whether metformin improves cardiac function (remodeling) in a long-term post-MI remodeling model. We therefore studied male, nondiabetic, Sprague-Dawley rats that were subjected to either myocardial infarction (MI) or sham operation. Animals were randomly allocated to treatment with normal water or metformin-containing water (250 mg·kg(-1)·day(-1)). At baseline, 6 wk, and 12 wk, metabolic parameters were analyzed and oral glucose tolerance tests (OGTT) were performed. Echocardiography and hemodynamic parameters were assessed 12 wk after MI. In the MI model, infarct size was significantly smaller after 12-wk metformin treatment (29.6 ± 3.2 vs. 38.0 ± 2.2%, P < 0.05). Moreover, metformin resulted in less left ventricular dilatation (6.0 ± 0.4 vs. 7.6 ± 0.6 mm, P < 0.05) and preservation of left ventricular ejection fraction (65.8 ± 3.7% vs. 48.6 ± 5.6%, P < 0.05) compared with MI control. The improved cardiac function was associated with decreased atrial natriuretic peptide mRNA levels in the metformin-treated group (50% reduction compared with MI, P < 0.05). Insulin resistance did not occur during cardiac remodeling (as indicated by normal OGTT) and fasting glucose levels and the pattern of the OGTT were not affected by metformin. Molecular analyses suggested that altered AMP kinase phosphorylation status and low insulin levels mediate the salutary effects of metformin. Altogether our results indicate that metformin may have potential to attenuate heart failure development after myocardial infarction, in the absence of diabetes and independent of systemic glucose levels.     

Bilateral sympathetic stellate ganglionectomy attenuates myocardial remodelling and fibrosis in a rat model of chronic volume overload

Reducing sympathetic neurohormone expression is a key therapeutic option in attenuating cardiac remodelling. Present study tested the feasibility of attenuating cardiac remodelling through reducing sympathetic neurohormone level by partial cardiac sympathetic denervation in a rat model of chronic volume overload. Male Sprague‐Dawley rats were randomized into sham group (S, n = 7), aortocaval fistula group (AV, n = 7), and aortocaval fistula with bilateral sympathetic stellate ganglionectomy group (AD, n = 8). After 12 weeks, myocardial protein expression of sympathetic neurohormones, including tyrosine hydroxylase, neuropeptide Y, growth associated protein 43, and protein gene product 9.5, were significantly up‐regulated in AV group compared to S group, and down‐regulated in AD group. Cardiac remodelling was aggravated in AV group compared to S group and attenuated in AD group. The myocardial deposition of extracellular matrix, including collagen I and III, was enhanced in AV group, which was reduced in AD group. Myocardial angiotensin II and aldosterone expressions were significantly up‐regulated in AV group and down‐regulated in AD group. Our results show that bilateral sympathetic stellate ganglionectomy could attenuate cardiac remodelling and fibrosis by down‐regulating sympathetic neurohormones expression in this rat model of chronic volume overload.     

Intramyocardial transplantation of cardiac telocytes decreases myocardial infarction and improves post‐infarcted cardiac function in rats

The midterm effects of cardiac telocytes (CTs) transplantation on myocardial infarction (MI) and the cellular mechanisms involved in the beneficial effects of CTs transplantation are not understood. In the present study, we have revealed that transplantation of CTs was able to significantly decrease the infarct size and improved cardiac function 14 weeks after MI. It has established that CT transplantation exerted a protective effect on the myocardium and this was maintained for at least 14 weeks. The cellular mechanism behind this beneficial effect on MI was partially attributed to increased cardiac angiogenesis, improved reconstruction of the CT network and decreased myocardial fibrosis. These combined effects decreased the infarct size, improved the reconstruction of the LV and enhanced myocardial function in MI. Our findings suggest that CTs could be considered as a potential cell source for therapeutic use to improve cardiac repair and function following MI, used either alone or in tandem with stem cells.     

Downregulation of interferon-induced protein with tetratricopeptide repeats 3 relieves the inflammatory response and myocardial fibrosis of mice with myocardial infarction and improves their cardiac function

Myocardial infarction (MI) is a common cardiovascular disease with high morbidity and mortality. In this study, we explored the role of interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) in MI. MI was induced by ligation of the left anterior descending coronary artery. Lentivirus-mediated RNA interference of IFIT3 expression was performed by tail vein injection 72 h before MI modeling. Cardiac injury indexes and inflammatory response were examined 3 days after MI. Cardiac function indexes, infarct size, and cardiac fibrosis were assessed 4 weeks after MI. IFIT3 expression was upregulated in myocardial tissues at both 3 days and 4 weeks after MI. Knockdown of IFIT3 significantly relieved the myocardial injury, as evidenced by the decrease in serum levels of cTnI and CK-MB. In addition, IFIT3 knockdown significantly reduced the number of CD68⁺ macrophages and the levels of interleukin-1β, interleukin-6, and tumor necrosis factor-α, indicating that the inflammatory response was relieved. Moreover, IFIT3 silencing also significantly improved cardiac function and reduced infarct size, myocardial fibrosis, and collagen content in mice with MI. Mechanically, the present study showed that the activation of the mitogen-activated protein kinase (MAPK) pathway was observed in myocardial tissues of MI mice, which was blocked by IFIT3 knockdown, as indicated by the decreased phosphorylation of JNK, p-38, and ERK. Collectively, our results revealed the role of IFIT3 in the inflammatory response and myocardial fibrosis after MI, indicating that IFIT3 might be a potential target for MI treatment.     

Immune regulation of cardiac fibrosis post myocardial infarction

Pathological changes resulting from myocardial infarction (MI) include extracellular matrix alterations of the left ventricle, which can lead to cardiac stiffness and impair systolic and diastolic function. The signals released from necrotic tissue initiate the immune cascade, triggering an extensive inflammatory response followed by reparative fibrosis of the infarct area. Immune cells such as neutrophils, monocytes, macrophages, mast cells, T-cells, and dendritic cells play distinct roles in orchestrating this complex pathological condition, and regulate the balance between pro-fibrotic and anti-fibrotic responses. This review discusses how molecular signals between fibroblasts and immune cells mutually regulate fibrosis post-MI, and outlines the emerging pharmacological targets and therapies for modulating inflammation and cardiac fibrosis associated with MI.     

Sustained delivery of VEGF from designer self-assembling peptides improves cardiac function after myocardial infarction

Canonical transient receptor potential (TRPC) channels are Ca(2+)-permeable, non-selective cation channels those are widely expressed in mammalian cells. Various molecules have been found to regulate TRPC both in vivo and in vitro, but it is unclear how heterotrimeric G proteins transmit external stimuli to regulate the activity of TRPC5. Here, we demonstrated that TRPC5 was potentiated by the Gα(s) regulatory pathway. Whole-cell TRPC5 current was significantly increased by β-adrenergic receptor agonist, isoproterenol (ISO, 246±36%, n=6), an activator of the adenylate cyclase, forskolin (FSK, 273±6%, n=5), or a membrane permeable cAMP analogue, 8-Br-cAMP (251±63%, n=7). In addition, robust Ca(2+) transient induced by isoproterenol was observed utilizing a Ca(2+) imaging technique. When intracellular [Ca(2+)](i) was buffered to 50nM, cAMP-induced potentiation was attenuated. We also found that the Ca(2+) release is mediated by IP(3) since intracellular IP(3) infusion attenuated the potentiation of TRPC5 by Gα(s) cascade. Finally, we identified that the membrane localization of TRPC5 was significantly increased by ISO (155±17%, n=3), FSK (172±39%, n=3) or 8-Br-cAMP (216±59%, n=3). In conclusion, these results suggest that the Gα(s)-cAMP pathway potentiates the activity of TRPC5 via facilitating intracellular Ca(2+) dynamics and increasing channel trafficking to the plasma membrane.