Naringin improves post-ischemic myocardial injury by activation of KATP channels.

Naringin (NRG) is a flavonoid with recognized cardioprotective effects. Then, it was investigated the cardioprotective mechanisms of NRG against ischemia-reperfusion (I/R) injury. The rats were pretreated for 7 days (v.o.) with NRG (25 mg/kg) or n-acetylcysteine (NAC, 100 mg/kg) and their isolated hearts were subjected to global ischemia (30 min) and reperfusion (60 min). Furthermore, isolated hearts were perfused with 5 µM NRG in the presence of 10 µM glibenclamide (GLI) and subjected to I/R protocol. In healthy ventricular cardiomyocyte, it was evaluated the acute effect of 5 µM NRG on the GLI sensitive current. The results showed that NRG pretreatment restored the cardiac function and electrocardiogram (ECG) alterations induced by I/R injury, decreasing arrhythmia scores and the occurrence of severe arrhythmias. Lactate dehydrogenase and infarct area were decreased while superoxide dismutase (SOD), catalase and citrate synthase activities increased. Expression of SOD CuZn and SOD Mn not was altered. NRG treatment decreased reactive oxygen species (ROS) generation and lipid peroxidation without alter sulfhydryl groups and protein carbonylation. Also, NRG (5 µM) increased the glibenclamide sensitive current in isolated cardiomyocytes. In isolated heart, the cardioprotection of NRG was significantly reduced by GLI. Furthermore, NRG promoted downregulation of Bax expression and Bax/Bcl-2. Histopathological analysis showed that NRG decreased cell edema, cardiomyocytes and nucleus diameter. Thus, NRG has a cardioprotective effect against cardiac I/R injury which is mediated by its antioxidant and antiapoptotic actions and KATP channels activation.

The positive inotropic effect of the ethyl acetate fraction from Erythrina velutina leaves on the mammalian myocardium: the role of adrenergic receptors.

OBJECTIVES: We studied the effects of ethyl acetate fraction (EAcF) obtained from Erythrina velutina leaves on mammalian myocardium. METHODS: The effect of EAcF on the contractility was studied using guinea-pig left atria mounted in a tissue bath (Tyrode's solution, 29°C, 95% CO2 , 5% O2 ) and electrically stimulated (1 Hz). Concentration-response curves of EAcF were obtained in the presence of propranolol (1 µm), nifedipine (1 µm) and in reserpinized animals (5 mg/kg). The involvement of l-type calcium current (ICa,L ) on the EAcF effect was observed in cardiomyocytes of mice assessed using patch-clamp technique. KEY FINDINGS: EAcF (550 µg/ml) had a positive inotropic effect, increasing the atrial force by 164% (EC50 = 157 ± 44 µg/ml, n = 6), but it was less potent than isoproterenol (EC50 = 0.0036 ± 0.0019 µg/ml, n = 8). The response evoked by EAcF was abolished by propranolol or nifedipine. Reserpine did not alter the inotropic response of EAcF. Furthermore, an enhancement of the ICa,L peak (31.2%) with EAcF was observed. Chemical analysis of EAcF revealed the presence of at least 10 different flavonoid glycoside derivatives. Two were identified as vicenin II and isorhoifolin. CONCLUSIONS: We conclude that EAcF increases the cardiac contractile force by increasing the l-type calcium current and activating the adrenergic receptor pathway.

R(+)-pulegone impairs Ca²+ homeostasis and causes negative inotropism in mammalian myocardium.

The present study aimed to investigate the inotropic effects of R(+)-pulegone, a monoterpene found in plant species belonging to the genus Mentha, on the mammalian heart. In electrically stimulated guinea pig atria, R(+)-pulegone reduced the contractile force (~83%) and decreased the contraction time measured at 50% of the maximum force amplitude (CT(50)) from 45.8 ± 6.2 ms to 36.9 ± 6.2 ms, suggesting that R(+)-pulegone may have an effect on Ca(2+) homeostasis. Nifedipine (40 µM), taken as a positive control, showed a very similar profile. To explore the hypothesis that R(+)-pulegone is somehow affecting Ca(2+) handling, we determined concentration-response curves for both CaCl(2) and BAY K8644. R(+)-pulegone shifted these curves rightward. Using isolated mouse ventricular cardiomyocytes, we measured whole-cell L-type Ca(2+) current and observed an I(Ca,L) peak reduction of 13.7 ± 2.5% and 40.2 ± 2.9% after a 3-min perfusion with 0.11 and 1.1mM of R(+)-pulegone, respectively. In addition, the intracellular Ca(2+) transient was decreased (72.9%) by 3.2mM R(+)-pulegone, with no significant changes in [Ca(2+)](i) transient decay kinetics. Moreover, R(+)-pulegone at 1.1mM prolonged the action potential duration at 10, 50, and 90% of repolarisation. The lengthening of the action potential duration may be attributed to the substantial blockade of the outward K(+) currents caused by 1.1mM of R(+)-pulegone (90.5% at 60 mV). These findings suggest that R(+)-pulegone exerts its negative inotropic effect on mammalian heart mainly by decreasing the L-type Ca(2+) current and the global intracellular Ca(2+) transient.