Objective To study the effect of overwork stress response on the expression of connexin 43（Cx43） and connexin 45（Cx45） in cardiomyocytes and on cardiac function. Methods The experimental animals were divided into control group, overworked 1-month group and overworked 2-month group. A overworked rat model was established by forcing swimming of overworked group. The expressions of Cx43 and Cx45 in myocardial tissues of experimental animals were detected by Western blotting, while the corresponding myocardial tissues were stained with hematoxylin-eosin （HE） staining and Masson's staining, then histologically observed. Results Western blotting results showed that, compared with the control group, Cx43 expression in myocardial tissues of overworked rats decreased while Cx45 expression increased. HE staining and Masson's staining results showed that hypertrophy, rupture and interstitial fiber tissue hyperplasia were observed in myocardial fibers of overworked rats. Conclusion Overwork stress response may affect cardiac function as an independent factor and may even cause heart failure or arrhythmias and lead to death.
Animals ; Arrhythmias, Cardiac/metabolism* ; Connexin 43/metabolism* ; Connexins/metabolism* ; Heart Failure ; Myocardium ; Myocytes, Cardiac/metabolism* ; Rats

Ischemia is the most common and important cause of injury to cardiomyocytes. Acute ischemia causes profound derangement of the cellular energetics and metabolism, and this ultimately leads to cell death. Experimental studies have demonstrated the presence of an endogenous protective mechanism that can diminish or delay cell death from ischemic insult; this is known as ischemic preconditioning. In this review, we summarize the recent knowledge of the cellular biology of acute ischemic injury and also signaling mechanisms of cardioprotection that are involved in preconditioning. Further, we briefly discuss the clinical implications.
Cell Death ; Ischemia* ; Ischemic Preconditioning ; Metabolism ; Myocytes, Cardiac*

In order to investigate the effects of aconitine on [Ca2+] oscillation patterns in cultured myocytes of neonatal rats, fluorescent Ca2+ indicator Fluo-4 NW and laser scanning confocal microscope (LSCM) were used to detect the real-time changes of [Ca2+] oscillation patterns in the cultured myocytes before and after aconitine (1.0 micromol/L) incubation or antiarrhythmic peptide (AAP) and aconitine co-incubation. The results showed under control conditions, [Ca2+] oscillations were irregular but relatively stable, occasionally accompanied by small calcium sparks. After incubation of the cultures with aconitine, high frequency [Ca2+] oscillations emerged in both nuclear and cytoplasmic regions, whereas typical calcium sparks disappeared and the average [Ca2+] in the cytoplasm of the cardiomyocyte did not change significantly. In AAP-treated cultures, intracellular [Ca2+] oscillation also changed, with periodic frequency, increased amplitudes and prolonged duration of calcium sparks. These patterns were not altered significantly by subsequent aconitine incubation. The basal value of [Ca2+] in nuclear region was higher than that in the cytoplasmic region. In the presence or absence of drugs, the [Ca2+] oscillated synchronously in both the nuclear and cytoplasmic regions of the same cardiomyocyte. It was concluded that although oscillating strenuously at high frequency, the average [Ca2+] in the cytoplasm of cardiomyocyte did not change significantly after aconitine incubation, compared to the controls. The observations indicate that aconitine induces the changes in [Ca2+] oscillation frequency other than the Ca2+ overload.
Aconitine/*pharmacology ; Animals, Newborn ; Calcium Signaling/*drug effects ; Cells, Cultured ; Myocytes, Cardiac/cytology ; Myocytes, Cardiac/*metabolism ; Rats, Sprague-Dawley

Burns ; complications ; metabolism ; Endotoxemia ; etiology ; metabolism ; Humans ; Multiple Organ Failure ; etiology ; metabolism ; Myocytes, Cardiac ; metabolism

The aim of the present paper was to study the role of sodium calcium exchanger (NCX) in the generation of action potentials (APs) in cardiomyocytes during early developmental stage (EDS). The precisely dated embryonic hearts of C57 mice were dissected and enzymatically dissociated to single cells. The changes of APs were recorded by whole-cell patch-clamp technique before and after administration of NCX specific blockers KB-R7943 (5 μmol/L) and SEA0400 (1 μmol/L). The results showed that, both KB-R7943 and SEA0400 had potent negative chronotropic effects on APs of pacemaker-like cells, while such effects were only observed in some ventricular-like cardiomyocytes. The negative chronotropic effect of KB-R7943 on ventricular-like cardiomyocytes was accompanied by shortening of AP duration (APD), whereas such an effect of SEA0400 was paralleled by decrease in velocity of diastolic depolarization (Vdd). From embryonic day 9.5 (E9.5) to E10.5, the negative chronotropic effects of KB-R7943 and SEA0400 on ventricular-like APs of embryonic cardiomyocytes gradually disappeared. These results suggest that, in the short-term development of early embryo, the function of NCX may experience developmental changes as evidenced by different roles of NCX in autorhythmicity and APs generation, indicating that NCX function varies with different conditions of cardiomyocytes.
Action Potentials ; Animals ; Calcium/metabolism* ; Mice ; Myocytes, Cardiac/metabolism* ; Sodium/metabolism* ; Sodium-Calcium Exchanger ; Thiourea/pharmacology*

Hyperglycemia is an important initiator of cardiovascular disease, contributing to the development of cardiomyocyte death and diabetic complications. The purpose of the present study was to investigate whether high glucose state could induce apoptosis of rat cardiomyocyte cell line H9c2 through microRNA-mediated Bcl-2 signaling pathway. The expression of miR-34a and Bcl-2 mRNA was detected by using real-time PCR. Western blotting was used to examine the changes in apoptosis-associated protein Bcl-2. Apoptosis of H9c2 cells was tested by using flow cytometry. The results showed that the expression of miR-34a was significantly elevated and that of Bcl-2 was strongly reduced, and apoptosis of cardiomyocytes was apparently increased in the high-glucose-treated H9c2 cells as compared with normal-glucose-treated controls. In addition, we identified Bcl-2 gene was the target of miR-34a. miR-34a mimics reduced the expression of Bcl-2 and increased glucose-induced apoptosis, but miR-34a inhibitor acted as the opposite mediator. Our data demonstrate that miR-34a contributes to high glucose-induced decreases in Bcl-2 expression and subsequent cardiomyocyte apoptosis.
Animals ; Apoptosis ; Cell Line ; Glucose ; metabolism ; MicroRNAs ; genetics ; metabolism ; Myocytes, Cardiac ; metabolism ; Rats

Humans ; Calcium/metabolism* ; Calmodulin ; Arrhythmias, Cardiac ; Calcium-Calmodulin-Dependent Protein Kinase Type 2/metabolism* ; Myocytes, Cardiac/metabolism* ; Phosphorylation

Postnatal heart maturation is the basis of normal cardiac function and provides critical insights into heart repair and regenerative medicine. While static snapshots of the maturing heart have provided much insight into its molecular signatures, few key events during postnatal cardiomyocyte maturation have been uncovered. Here, we report that cardiomyocytes (CMs) experience epigenetic and transcriptional decline of cardiac gene expression immediately after birth, leading to a transition state of CMs at postnatal day 7 (P7) that was essential for CM subtype specification during heart maturation. Large-scale single-cell analysis and genetic lineage tracing confirm the presence of transition state CMs at P7 bridging immature state and mature states. Silencing of key transcription factor JUN in P1-hearts significantly repressed CM transition, resulting in perturbed CM subtype proportions and reduced cardiac function in mature hearts. In addition, transplantation of P7-CMs into infarcted hearts exhibited cardiac repair potential superior to P1-CMs. Collectively, our data uncover CM state transition as a key event in postnatal heart maturation, which not only provides insights into molecular foundations of heart maturation, but also opens an avenue for manipulation of cardiomyocyte fate in disease and regenerative medicine.
Gene Expression Regulation ; Heart ; Myocytes, Cardiac/metabolism* ; Single-Cell Analysis ; Transcription Factors/metabolism*

Cardiomyocytes injury model has been widely used in the study for the molecular mechanism of cardiovascular diseases and drug action. It is very important to select the appropriate model due to the different formation mechanisms for various models. Clinical cardiovascular pathological change is relatively complex. Currently used models according to the characteristics of clinical cardiovascular diseases mainly include hydrogen peroxide-induced myocardial cell damage model, hypoxia reoxygenation injury model, adriamycin-induced myocardial cell damage model, high sugar high fat-induced myocardial cell damage model, and isoprenaline-induced myocardial cell damage model. Every model has its advantages as well as its disadvantages. The suitable model of myocardial cell injury can be selected according to the research purpose.
Animals ; Cell Hypoxia ; Myocardial Reperfusion Injury/metabolism* ; Myocardium ; Myocytes, Cardiac/metabolism* ; Rats ; Rats, Sprague-Dawley ; Research

BackgroundOxygen-glucose deprivation-nutrition resumption (OGD-NR) models on H9c2 cells are commonly used in vitro models of simulated myocardial ischemia-reperfusion injury (MIRI), but no study has assessed whether these methods for establishing in vitro models can effectively imitate the characteristics of MIRI in vivo. This experiment was designed to analyze the feasibility of six OGD-NR models of MIRI.

MethodsBy searching the PubMed database using the keywords "myocardial reperfusion injury H9c2 cells," we obtained six commonly used OGD-NR in vitro models of MIRI performed on H9c2 cells from more than 400 published papers before January 30, 2017. For each model, control (C), simulated ischemia (SI), and simulated ischemia-reperfusion (SIR) groups were assigned, and cell morphology, lactate dehydrogenase (LDH) release, adenosine triphosphate (ATP) levels, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and inflammatory cytokines were examined to evaluate the characteristics of cell injury. Subsequently, a coculture system of cardiomyocyte-endothelial-macrophage was constructed. The coculture system was dealt with SI and SIR treatments to test the effect on cardiomyocytes survival.

ResultsFor models 1, 2, 3, 4, 5, and 6, SI treatment caused morphological damage to cells, and subsequent SIR treatment did not cause further morphological damage. In the models 1, 2, 3, 4, 5 and 6, LDH release was significantly higher in the SI groups than that in the C group (P < 0.05), and was significantly lower in the SIR groups than that in the SI groups (P < 0.05), except for no significant differences in the LDH release between C, SI and SIR groups in model 6 receiving a 3-h SI treatment. In models 1, 2, 3, 4, 5, and 6, compared with the C group, ATP levels of the SI groups significantly decreased (P < 0.05), ROS levels increased (P < 0.05), and MMP levels decreased (P < 0.05). Compared with the SI group, ATP level of the SIR groups was significantly increased (P < 0.05), and there was no significant ROS production, MMP collapse, and over inflammatory response in the SIR groups. In a coculture system of H9c2 cells-endothelial cells-macrophages, the proportion of viable H9c2 cells in the SIR groups was not reduced compared with the SI groups.

ConclusionAll the six OGD-NR models on H9c2 cells in this experiment can not imitate the characteristics of MIRI in vivo and are not suitable for MIRI-related study.

Apoptosis ; Glucose ; metabolism ; Humans ; Myocardial Reperfusion Injury ; physiopathology ; Myocytes, Cardiac ; physiology ; Oxygen ; metabolism