Rationale Cardiovascular disease represents a global pandemic. The advent of and recent advances in mouse genomics, epigenomics, and transgenics offer ever-greater potential for powerful avenues of research. However, progress is often constrained by unique complexities associated with the isolation of viable myocytes from the adult mouse heart. Current protocols rely on retrograde aortic perfusion using specialized Langendorff apparatus, which poses considerable logistical and technical barriers to researchers and demands extensive training investment. Objective To identify and optimize a convenient, alternative approach, allowing the robust isolation and culture of adult mouse cardiac myocytes using only common surgical and laboratory equipment. Methods and Results Cardiac myocytes were isolated with yields comparable to those in published Langendorff-based methods, using direct needle perfusion of the LV ex vivo and without requirement for heparin injection. Isolated myocytes can be cultured antibiotic free, with retained organized contractile and mitochondrial morphology, transcriptional signatures, calcium handling, responses to hypoxia, neurohormonal stimulation, and electric pacing, and are amenable to patch clamp and adenoviral gene transfer techniques. Furthermore, the methodology permits concurrent isolation, separation, and coculture of myocyte and nonmyocyte cardiac populations. Conclusions We present a novel, simplified method, demonstrating concomitant isolation of viable cardiac myocytes and nonmyocytes from the same adult mouse heart. We anticipate that this new approach will expand and accelerate innovative research in the field of cardiac biology.

Our data provide a detailed circRNA expression landscape in hearts. There is a high-abundance of specific cardiac-expressed circRNA. These findings open up a new avenue for future investigation into this emerging class of RNA.

Distinct epigenomic patterns exist in important DNA elements of the cardiac genome in human end-stage cardiomyopathy. The epigenome may control the expression of local or distal genes with critical functions in myocardial stress response. If epigenomic patterns track with disease progression, assays for the epigenome may be useful for assessing prognosis in heart failure. Further studies are needed to determine whether and how the epigenome contributes to the development of cardiomyopathy.

Cardiac hypertrophy is a growth response of the heart to increased hemodynamic demand or damage. Accompanying this heart enlargement is a remodeling of Ca 2؉ signaling. Due to its fundamental role in controlling cardiomyocyte contraction during every heartbeat, modifications in Ca 2؉ fluxes significantly impact on cardiac output and facilitate the development of arrhythmias. Using cardiomyocytes from spontaneously hypertensive rats (SHRs), we demonstrate that an increase in Ca 2؉ release through inositol 1,4,5-trisphosphate receptors (InsP 3Rs) contributes to the larger excitation contraction coupling (ECC)-mediated Ca 2؉ transients characteristic of hypertrophic myocytes and underlies the more potent enhancement of ECCmediated Ca 2؉ transients and contraction elicited by InsP3 or endothelin-1 (ET-1). Responsible for this is an increase in InsP 3R expression in the junctional sarcoplasmic reticulum. Due to their close proximity to ryanodine receptors (RyRs) in this region, enhanced Ca 2؉ release through InsP 3Rs served to sensitize RyRs, thereby increasing diastolic Ca 2؉ levels, the incidence of extra-systolic Ca 2؉ transients, and the induction of ECC-mediated Ca 2؉ elevations. Unlike the increase in InsP 3R expression and Ca 2؉ transient amplitude in the cytosol, InsP3R expression and ECC-mediated Ca 2؉ transients in the nucleus were not altered during hypertrophy. Elevated InsP 3R2 expression was also detected in hearts from human patients with heart failure after ischemic dilated cardiomyopathy, as well as in aortic-banded hypertrophic mouse hearts. Our data establish that increased InsP 3R expression is a general mechanism that underlies remodeling of Ca 2؉ signaling during heart disease, and in particular, in triggering ventricular arrhythmia during hypertrophy.calcium ͉ ECC ͉ IP3 ͉ SHR ͉ signalling