Ketamine attenuates the Na+-dependent Ca2+ overload in rabbit ventricular myocytes in vitro by inhibiting late Na+ and L-type Ca2+ currents

COVID-19: the CaMKII-like system of S protein drives membrane fusion and induces syncytial multinucleated giant cells

The SARS-CoV-2 S protein on the membrane of infected cells can promote receptor-dependent syncytia formation, relating to extensive tissue damage and lymphocyte elimination. In this case, it is challenging to obtain neutralizing antibodies and prevent them through antibodies effectively. Considering that, in the current study, structural domain search methods are adopted to analyze the SARS-CoV-2 S protein to find the fusion mechanism. The results show that after the EF-hand domain of S protein bound to calcium ions, S2 protein had CaMKII protein activities. Besides, the CaMKII_AD domain of S2 changed S2 conformation, facilitating the formation of HR1-HR2 six-helix bundles. Apart from that, the Ca²⁺-ATPase of S2 pumped calcium ions from the virus cytoplasm to help membrane fusion, while motor structures of S drove the CaATP_NAI and CaMKII_AD domains to extend to the outside and combined the viral membrane and the cell membrane, thus forming a calcium bridge. Furthermore, the phospholipid-flipping-ATPase released water, triggering lipid mixing and fusion and generating fusion pores. Then, motor structures promoted fusion pore extension, followed by the cytoplasmic contents of the virus being discharged into the cell cytoplasm. After that, the membrane of the virus slid onto the cell membrane along the flowing membrane on the gap of the three CaATP_NAI. At last, the HR1-HR2 hexamer would fall into the cytoplasm or stay on the cell membrane. Therefore, the CaMKII_like system of S protein facilitated membrane fusion for further inducing syncytial multinucleated giant cells.

Antiarrhythmic effect of crotonoside by regulating sodium and calcium channels in rabbit ventricular myocytes

AIMS

Detect the antiarrhythmic effect of crotonoside (Cro).

MAIN METHODS

We used whole-cell patch-clamp techniques to detect the effects of Cro on action potentials (APs) and transmembrane ion currents in isolated rabbit left ventricular myocytes. We also verified the effect of Cro on ventricular arrhythmias caused by aconitine in vivo.

KEY FINDINGS

Cro reduced the maximum depolarization velocity (V_max) of APs and shortened the action potential duration (APD) in a concentration-dependent manner, but it had no significant effect on the resting membrane potential (RMP) or action potential amplitude (APA). It also inhibited the peak sodium current (I_Na) and L-type calcium current (I_CaL) in a concentration-dependent manner with half-maximal inhibitory concentrations (IC₅₀) of 192 μmol/L and 159 μmol/L, respectively. However, Cro had no significant effects on the inward rectifier potassium current (I_K1) or rapidly activating delayed rectifier potassium current (I_Kr). Sea anemone toxin II (ATX II) increased the late sodium current (I_NaL), but Cro abolished this effect. Moreover, Cro significantly abolished ATX II-induced early afterdepolarizations (EADs) and high extracellular Ca²⁺ concentration (3.6 mmol/L)-induced delayed afterdepolarizations (DADs). We also verified that Cro effectively delayed the onset time and reduced the incidence of ventricular arrhythmias caused by aconitine in vivo.

SIGNIFICANCE

These results revealed that Cro effectively inhibits I_Na, I_NaL, and I_CaL in ventricular myocytes. Cro has antiarrhythmic potential and thus deserves further study.

Neurokinin-1 receptor antagonist decreases [Ca2+]i in airway smooth muscle cells by reducing the reverse-mode Na+/Ca2+ exchanger current

Airway smooth muscle (ASM) is involved in asthma airway inflammation. The aim of this study was to evaluate the effect of substance P and neurokinin-1 receptor (NK-1R) antagonist on intracellular calcium concentration ([Ca²⁺]i) in airway smooth muscle cells (ASMCs), ASMC contraction, and the effect on reverse-mode Na⁺-Ca²⁺ exchanger (NCX) currents in ASMCs. In our study, primary rat ASMCs were cultured. ASMCs were identified by immunofluorescence. [Ca²⁺]i variations were measured by fluorescence microscopy. Cell shortening (%) and relaxation (%) were analyzed with phase-contrast microscopy. Patch clamp techniques were used to assess NCX currents in ASMCs. We found that substance P increased, and NK-1R antagonist decreased [Ca²⁺]i in ASMCs. Substance P induced ASMCs contraction, and NK-1R antagonist can make ASMC relax. Patch clamp techniques were implemented to analyze NCX currents in ASMCs. Substance P increased reverse-mode NCX currents in ASMCs but the current density was lower than the one treated with acetylcholine (Ach). NK-1R antagonist reduced reverse-mode NCX current activity in ASMCs, and the current density was similar to the one treated with the reversed NCX inhibitor. So, we concluded that substance P increased [Ca²⁺]i in ASMCs by promoting the reverse-mode NCX current and stimulating ASMCs, whereas NK-1R antagonist decreased [Ca²⁺]i in ASMCs by decreasing the reverse-mode NCX current to make ASMCs relax.

Barbaloin inhibits ventricular arrhythmias in rabbits by modulating voltage-gated ion channels

Barbaloin (10-β-D-glucopyranosyl-1,8-dihydroxy-3-(hydroxymethyl)-9(10H)-anthracenone) is extracted from the aloe plant and has been reported to have anti-inflammatory, antitumor, antibacterial, and other biological activities. Here, we investigated the effects of barbaloin on cardiac electrophysiology, which has not been reported thus far. Cardiac action potentials (APs) and ionic currents were recorded in isolated rabbit ventricular myocytes using whole-cell patch-clamp technique. Additionally, the antiarrhythmic effect of barbaloin was examined in Langendorff-perfused rabbit hearts. In current-clamp recording, application of barbaloin (100 and 200 μmol/L) dose-dependently reduced the action potential duration (APD) and the maximum depolarization velocity (Vmax), and attenuated APD reverse-rate dependence (RRD) in ventricular myocytes. Furthermore, barbaloin (100 and 200 μmol/L) effectively eliminated ATX II-induced early afterdepolarizations (EADs) and Ca²⁺-induced delayed afterdepolarizations (DADs) in ventricular myocytes. In voltage-clamp recording, barbaloin (10-200 μmol/L) dose-dependently inhibited L-type calcium current (I_Ca.L) and peak sodium current (I_Na.P) with IC₅₀ values of 137.06 and 559.80 μmol/L, respectively. Application of barbaloin (100, 200 μmol/L) decreased ATX II-enhanced late sodium current (I_Na.L) by 36.6%±3.3% and 71.8%±6.5%, respectively. However, barbaloin up to 800 μmol/L did not affect the inward rectifier potassium current (I_K1) or the rapidly activated delayed rectifier potassium current (I_Kr) in ventricular myocytes. In Langendorff-perfused rabbit hearts, barbaloin (200 μmol/L) significantly inhibited aconitine-induced ventricular arrhythmias. These results demonstrate that barbaloin has potential as an antiarrhythmic drug.

Olesoxime Inhibits Cardioplegia-Induced Ischemia/Reperfusion Injury. A Study in Langendorff-Perfused Rabbit Hearts

Objective: During cardioplegia, which is often used in cardiac surgery, the heart is subjected to global ischemia/reperfusion injury, which can result in a post-operative impairment of cardiac function. Mitochondria permeability transition pores (MPTP) play a key role in cardiomyocyte survival after ischemia/reperfusion injury. It was shown in clinical settings that blockers of MPTP like cyclosporine might have a positive influence on cardiac function after cardioplegic arrest. Olesoxime, which is a new drug with MPTP blocking activity, has been introduced as a neuroprotective therapeutic agent. This drug has not been investigated on a possible positive effect in ischemia/reperfusion injury in hearts. Therefore, the aim of our study was to investigate possible effects of olesoxime on cardiac recovery after cardioplegic arrest.

Methods: We evaluated 14 mature Chinchilla bastard rabbits of 1,500–2,000 g. Rabbit hearts were isolated and perfused with constant pressure according to Langendorff. After induction of cardioplegic arrest (30 ml 4°C cold Custodiol cardioplegia without and with 5 μmol/L olesoxime, n = 7 each) the hearts maintained arrested for 90-min. Thereafter, the hearts were re-perfused for 60 min. At the end of each experiment left ventricular samples were frozen in liquid nitrogen for ATP measurements. Furthermore, heart slices were embedded in paraffin for histological analysis. During the entire experiment hemodynamic and functional data such as left ventricular pressure (LVP), dp/dt(max) and (min), pressure rate product (PRP), coronary flow, pO₂, and pCO₂ were also assessed.

Results: Histological analysis revealed that despite the same ischemic burden for both groups markers of nitrosative and oxidative stress were significantly lower in the olesoxime group. Moreover, hearts of the olesoxime-group showed a significantly faster and better hemodynamic recovery during reperfusion. In addition, tissue ATP-levels were significantly higher in the olesoxime treated hearts.

Conclusions: Olesoxime significantly protected the cardiac muscle from ischemia/reperfusion injury.

Potential new mechanisms of pro-arrhythmia in arrhythmogenic cardiomyopathy: focus on calcium sensitive pathways

Arrhythmogenic cardiomyopathy, or its most well-known subform arrhythmogenic right ventricular cardiomyopathy (ARVC), is a cardiac disease mainly characterised by a gradual replacement of the myocardial mass by fibrous and fatty tissue, leading to dilatation of the ventricular wall, arrhythmias and progression towards heart failure. ARVC is commonly regarded as a disease of the intercalated disk in which mutations in desmosomal proteins are an important causative factor. Interestingly, the Dutch founder mutation PLN R14Del has been identified to play an additional, and major, role in ARVC patients within the Netherlands. This is remarkable since the phospholamban (PLN) protein plays a leading role in regulation of the sarcoplasmic reticulum calcium load rather than in the establishment of intercellular integrity. In this review we outline the intracellular cardiac calcium dynamics and relate pathophysiological signalling, induced by disturbed calcium handling, with activation of calmodulin dependent kinase II (CaMKII) and calcineurin A (CnA). We postulate a thus far unrecognised role for Ca2+ sensitive signalling proteins in maladaptive remodelling of the macromolecular protein complex that forms the intercalated disk, during pro-arrhythmic remodelling of the heart.

Tolterodine reduces veratridine-augmented late INa, reverse-INCX and early afterdepolarizations in isolated rabbit ventricular myocytes

AIM

The augmentation of late sodium current (I_Na.L) not only causes intracellular Na⁺ accumulation, which results in intracellular Ca²⁺ overload via the reverse mode of the Na⁺/Ca²⁺ exchange current (reverse-I_NCX), but also prolongs APD and induces early afterdepolarizations (EAD), which can lead to arrhythmia and cardiac dysfunction. Thus, the inhibition of I_Na.L is considered to be a potential way for therapeutic intervention in ischemia and heart failure. In this study we investigated the effects of tolterodine (Tol), a competitive muscarinic receptor antagonist, on normal and veratridine (Ver)-augmented I_Na.L, reverse-I_NCX and APD in isolated rabbit ventricular myocytes, which might contribute to its cardioprotective activity.

METHODS

Rabbit ventricular myocytes were prepared. The I_Na.L and reverse-I_NCX were recorded in voltage clamp mode, whereas action potentials and Ver-induced early afterdepolarizations (EADs) were recorded in current clamp mode. Drugs were applied via superfusion.

RESULTS

Tol (3-120 nmol/L) concentration-dependently inhibited the normal and Ver-augmented I_Na.L with IC₅₀ values of 32.08 nmol/L and 42.47 nmol/L, respectively. Atropine (100 μmol/L) did not affect the inhibitory effects of Tol (30 nmol/L) on Ver-augmented I_Na.L. In contrast, much high concentrations of Tol was needed to inhibit the transient sodium current (I_Na.T) with an IC₅₀ value of 183.03 μmol/L. In addition, Tol (30 nmol/L) significantly shifted the inactivation curve of I_Na.T toward a more depolarizing membrane potential without affecting its activation characteristics. Moreover, Tol (30 nmol/L) significantly decreased Ver-augmented reverse-I_NCX. Tol (30 nmol/L) increased the action potential duration (APD) by 16% under the basal conditions. Ver (20 μmol/L) considerably extended the APD and evoked EADs in 18/24 cells (75%). In the presence of Ver, Tol (30 nmol/L) markedly decreased the APD and eliminated EADs (0/24 cells).

CONCLUSION

Tol inhibits normal and Ver-augmented I_NaL and decreases Ver-augmented reverse-I_NCX. In addition, Tol reverses the prolongation of the APD and eliminates the EADs induced by Ver, thus prevents Ver-induced arrhythmia.