Postnatal developmental changes in the sensitivity of L-type Ca2+ channel to inhibition by verapamil in a mouse heart model

Protective effect of ginsenoside Rb1 against aconitine cardiotoxicity studied by myocardial injury, action potential, and calcium signaling

Aconitine is the main active component of Aconitum plants. Although aconitine has effects that include strengthening the heart, analgesia, anti-tumor, and immune-regulating effects, aconitine has both efficacy and toxicity, especially cardiotoxicity. Severe effects can include arrhythmia and cardiac arrest, which limits the clinical application of aconitine-containing traditional Chinese medicine. Ginsenoside Rb1(Rb1) is mainly found in plants, such as ginseng and Panax notoginseng, and has cardiovascular-protective and anti-arrhythmia effects. This study aimed to investigate the detoxifying effects of Rb1 on aconitine cardiotoxicity and the electrophysiological effect of Rb1 on aconitine-induced arrhythmia in rats. Pathological analysis, myocardial enzymatic indexes, and Western blotting were used to investigate the ameliorating effect of Rb1 on aconitine cardiotoxicity. Optical mapping was used to evaluate the effect of Rb1 on action potential and calcium signaling after aconitine-induced arrhythmia. Rb1 inhibited pathological damage caused by aconitine, decreased myocardial enzyme levels, and restored the balance of apoptotic protein expression by reducing the expression of Bax and cleaved caspase 3 and increasing the expression of Bcl-2, thereby reducing myocardial damage caused by aconitine. Rb1 also reduced the increase in heart rate caused by aconitine, accelerated action potential conduction and calcium signaling, and reduced the dispersion of action potential and calcium signal conduction. Rb1 reduced the cardiotoxicity of aconitine by attenuating aconitine-induced myocardial injury and inhibiting the aconitine-induced retardation of ventricular action potential and calcium signaling in rats.

Identification of RNA reads encoding different channels in isolated rat ventricular myocytes and the effect of cell stretching on L-type Ca2+current

BACKGROUND

The study aimed to identify transcripts of specific ion channels in rat ventricular cardiomyocytes and determine their potential role in the regulation of ionic currents in response to mechanical stimulation. The gene expression levels of various ion channels in freshly isolated rat ventricular cardiomyocytes were investigated using the RNA-seq technique. We also measured changes in current through CaV1.2 channels under cell stretching using the whole-cell patch-clamp method.

RESULTS

Among channels that showed mechanosensitivity, significant amounts of TRPM7, TRPC1, and TRPM4 transcripts were found. We suppose that the recorded L-type Ca2+ current is probably expressed through CaV1.2. Furthermore, stretching cells by 6, 8, and 10 μm, which increases ISAC through the TRPM7, TRPC1, and TRPM4 channels, also decreased ICa,L through the CaV1.2 channels in K+ in/K+ out, Cs+ in/K+ out, K+ in/Cs+ out, and Cs+ in/Cs+ out solutions. The application of a nonspecific ISAC blocker, Gd3+, during cell stretching eliminated ISAC through nonselective cation channels and ICa,L through CaV1.2 channels. Since the response to Gd3+ was maintained in Cs+ in/Cs+ out solutions, we suggest that voltage-gated CaV1.2 channels in the ventricular myocytes of adult rats also exhibit mechanosensitive properties.

CONCLUSIONS

Our findings suggest that TRPM7, TRPC1, and TRPM4 channels represent stretch-activated nonselective cation channels in rat ventricular myocytes. Probably the CaV1.2 channels in these cells exhibit mechanosensitive properties. Our results provide insight into the molecular mechanisms underlying stretch-induced responses in rat ventricular myocytes, which may have implications for understanding cardiac physiology and pathophysiology.

An improved procedure for isolating adult mouse cardiomyocytes for epicardial activation mapping

Cardiovascular disease is a leading cause of death and disability worldwide. Although genetically modified mouse models offer great potential for robust research in vivo, in vitro studies using isolated cardiomyocytes also provide an important approach for investigating the mechanisms underlying cardiovascular disease pathogenesis and drug actions. Currently, isolation of mouse adult cardiomyocytes often relies on aortic retrograde intubation under a stereoscopic microscope, which poses considerable technical barriers and requires extensive training. Although a simplified, Langendorff-free method has been used to isolate viable cardiomyocytes from the adult mouse heart, the system requires enzymatic digestions and continuous manual technical operation. This study established an optimized approach that allows isolation of adult mouse cardiomyocytes and epicardial activation mapping of mouse hearts using a Langendorff device. We used retrograde puncture through the abdominal aorta in vivo and enzymatic digestion on the Langendorff perfusion device to isolate adult mouse cardiomyocytes without using a microscope. The yields of isolated cardiomyocytes were amenable to patch clamp techniques. Furthermore, this approach allowed epicardial activation mapping. We used a novel, simplified method to isolate viable cardiomyocytes from adult mouse hearts and to map epicardial activation. This novel approach could be beneficial in more extensive research in the cardiac field.

Nifedipine disturbs fetal cardiac function during hypoxemia in a chronic sheep model at near term gestation

BACKGROUND

Nifedipine is a widely used drug in pregnancies complicated by maternal hypertensive disorders that can be associated with placental insufficiency and fetal hypoxemia. The evidence regarding fetal myocardial responses to nifedipine in hypoxemia is limited.

OBJECTIVE

We hypothesized that nifedipine would not impair fetal sheep cardiac function under hypoxemic environment. In particular, we investigated the effects of nifedipine on fetal ventricular functional parameters and cardiac output.

STUDY DESIGN

A total of 21 chronically instrumented fetal sheep at 122 to 134 gestational days (term, 145 days) were included in this study. Fetal cardiac function was evaluated by measuring global longitudinal strain, indices describing ventricular systolic and diastolic function, and cardiac outputs using two-dimensional speckle tracking and tissue and spectral pulsed-wave Doppler echocardiography. Fetal carotid artery blood pressure and blood gas values were invasively monitored. After baseline data collection, fetal hypoxemia was induced by maternal hyperoxygenation. After hypoxemia phase data collection, 9 fetuses received nifedipine infusion, and 12 fetuses received saline infusion. Data were collected 30 and 120 minutes after the infusion was started. After 120 minutes of data collection, maternal and fetal oxygenation were normalized, and normoxemia phase data were collected, while infusion was continued.

RESULTS

Hypoxemia decreased fetal carotid artery mean arterial pressure from 40 (8) mm Hg to 35 (8) mm Hg (P<.007), and left ventricular global longitudinal strain showed less deformation than at baseline (P=.001). Under hypoxemia, nifedipine caused a reduction in right ventricular global longitudinal strain (P<.05), a decrease in right ventricular isovolumic relaxation velocity and its deceleration (P<.01) indicating diastolic dysfunction, and a drop in right ventricular cardiac output (P<.05). Nifedipine did not alter fetal left ventricular functional parameters or cardiac output. When normoxemia was restored, fetal right ventricular functional parameters and cardiac output returned to baseline level.

CONCLUSION

In hypoxemic fetus, nifedipine impaired right ventricular function and reduced its cardiac output. The detrimental effects of nifedipine on fetal right ventricular function were abolished, when normoxemia was restored. Our findings suggest that in a hypoxemic environment nifedipine triggers detrimental effects on fetal right ventricular function.

Ginsenoside Rb1 ameliorates cardiotoxicity triggered by aconitine via inhibiting calcium overload and pyroptosis

BACKGROUND

Aconitine-induced cardiotoxicity limits the clinical treatment of cardiotonic, cancers and immune-related diseases. Ginsenoside Rb1 (Rb1) is an active ingredient of traditional Chinese medicine with cardioprotective effect.

PURPOSE

This study aims to study the mechanism of aconitine cardiotoxicity and the detoxification mechanism of Rb1.

STUDY DESIGN

METHODS: The regulatory effect of Rb1 on aconitine was evaluated in vitro and in vivo by myocardial enzyme indicators, pathological analysis, CardioECR detection, calcium transient analysis, western blotting and immunohistochemistry.

RESULTS

Rb1 (10, 20, 40 mg/kg) alleviated apoptotic myocardial damage caused by aconitine in rats. Furthermore, Rb1 (25, 50, 100 μM) restored the contractile function and field potential of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) by regulating calcium channels and reduced myocardial cell damage by inhibiting the calcium transients of adult rat ventricular myocytes (ARVMs). Rb1 significantly reduced calcium levels in hiPSC-CMs, directly indicating that aconitine-induced calcium overload was alleviated by Rb1. Further, aconitine caused calcium overload by changing the expression of calcium pathway proteins, while Rb1 effectively restored calcium homeostasis. In addition, Rb1 also had a cardioprotective role by inhibiting cell pyroptosis. These results suggested that the maintenance of calcium homeostasis helped to suppress the inflammatory response related to pyroptosis of the heart.

CONCLUSION

Aconitine-induced cardiotoxicity can be alleviated by Rb1 via restoring calcium homeostasis and inhibiting apoptosis and pyroptosis.