Effect of angiotensin converting enzyme inhibitor on the calcium transients and calcium handling proteins in ventricular myocytes from rats with heart failure

Background Chronic heart failure (CHF) is associated with calcium transients and calcium handling proteins. Angiotensin converting enzyme (ACE) inhibitor has been demonstrated to have beneficial effect on CHF. Yet studies addressed to the relationship between ACE inhibitor and calcium transients in CHF are rare. The aim of this study was to investigate the influence of ACE inhibitor (perindopril) on the contractility and calcium transients and calcium handling proteins in ventricular myocytes from rats with experimental heart failure.Methods Male Wistar rats were randomized to heart failure group treated with perindopril (CHF-T, 3 mg·kg -1 ·d -1 ), heart failure group without treatment (CHF-C) and sham-operated group (PS). Heart failure was induced by abdominal aortic constriction. All groups were further followed up for 12 weeks. Left ventricular myocytes were then isolated. Single cell shortening fraction and [Ca 2+ ]_i were simultaneously measured by laser scanning confocal microscope under the field stimulation (1.0 Hz). Reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot were performed to evaluate the changes of mRNA and protein of Na +-Ca 2+ exchanger (NCX_1), sarcoplasmic reticulum Ca 2+ -ATPase (SERCA_2) and phospholamban (PLB).Results The fraction of cell shortening (FS%) and [Ca 2+ ]_ imax (nmol/L) were significantly reduced in group CHF-C compared with group PS (FS%: 7.51±1.15 vs 13.21±1.49;[Ca 2+ ]_ imax :330.85±50.05 vs 498.16±14.07; both P <0.01), and restored at least partially in CHF-T group. In CHF-C group, the left ventricular mRNA of NCX_1 and PLB were significantly upregulated in comparing with PS group (R_ NCX1/β-Actin : 0.51±0.12 vs 0.19±0.06, P <0.01; R_ PLB/β-Actin : 0.26±0.12 vs 0.20±0.08, P <0.05), while SERCA_2 mRNA was downregulated (0.48±0.10 vs 0.80±0.11, P <0.01). The mRNA levels of NCX_1 and SERCA_2 in CHF-T group were between the CHF-C and PS group, and the differences of the latter two groups were significant (all P <0.05). In CHF-C and CHF-T groups, the protein expression of NCX_1 were 1.141±0.047 and 1.074±0.081 times of that in PS group respectively (both P <0.05), and SERCA_2 protein levels were 0.803±0.100 and 0.893±0.084 times of that in PS group respectively (both P <0.05). The protein expression of NCX_1 and SERCA_2 in the CHF-C and CHF-T groups is significantly different (both P <0.05).ConclusionACE inhibitor could improve cardiac function of failing heart through directly enhancing the contractility of single cardiomyocyte, and these effects are probably mediated by its roles in preventing the deleterious changes of calcium transients and calcium handling proteins in CHF.

Cardiac BIN1(cBIN1) is a regulator of cardiac contractile function and an emerging biomarker of heart muscle health

In recent decades,a cardiomyocyte membrane scaffolding protein bridging integrator 1(BIN1) has emerged as a critical multifunctional regulator of transverse-tubule(t-tubule) function and calcium signaling in cardiomyocytes.Encoded by a single gene with 20 exons that are alternatively spliced,more than ten BIN1 protein isoforms are expressed with tissue and disease specificity.The recently discovered cardiac alternatively spliced isoform BIN1(cBIN1 or BIN1 +13 + 17)plays a crucial role in organizing membrane microfolds within cardiac t-tubules.These cBIN1-induced microfolds form functional dyad microdomains by trafficking L-type calcium channels(LTCC) to t-tubule membrane and recruiting ryanodine receptors(RyR) to junctional sarcoplasmic reticulum membrane.When cBIN1 is transcriptionally reduced as occurs in heart failure,cBIN1-microfolds are disrupted and fail to form LTCC and RyR couplons.As a result,impaired dyad formation limits excitation-contraction coupling thus cardiac contractility,and accumulation of orphaned leaky RyRs outside of dyads increases ventricular arrhythmias.Reduced myocardial BIN1 in heart failure is also detectable at the blood level,and plasma BIN1 level predicts heart failure progression and future arrhythmias in cardiomyopathy patients.Here we will review the recent progress in BIN1-related cardiomyocyte biology studies and discuss the diagnostic and predictive values of cBIN1 in future clinical use.