Contractile Function During Angiotensin-II Activation: Increased Nox2 Activity Modulates Cardiac Calcium Handling via Phospholamban Phosphorylation.

BACKGROUND: Renin-angiotensin system activation is a feature of many cardiovascular conditions. Activity of myocardial reduced nicotinamide adenine dinucleotide phosphate oxidase 2 (NADPH oxidase 2 or Nox2) is enhanced by angiotensin II (Ang II) and contributes to increased hypertrophy, fibrosis, and adverse remodeling. Recent studies found that Nox2-mediated reactive oxygen species production modulates physiological cardiomyocyte function. OBJECTIVES: This study sought to investigate the effects of cardiomyocyte Nox2 on contractile function during increased Ang II activation. METHODS: We generated a cardiomyocyte-targeted Nox2-transgenic mouse model and studied the effects of in vivo and ex vivo Ang II stimulation, as well as chronic aortic banding. RESULTS: Chronic subpressor Ang II infusion induced greater cardiac hypertrophy in transgenic than wild-type mice but unexpectedly enhanced contractile function. Acute Ang II treatment also enhanced contractile function in transgenic hearts in vivo and transgenic cardiomyocytes ex vivo. Ang II-stimulated Nox2 activity increased sarcoplasmic reticulum (SR) Ca(2+) uptake in transgenic mice, increased the Ca(2+) transient and contractile amplitude, and accelerated cardiomyocyte contraction and relaxation. Elevated Nox2 activity increased phospholamban phosphorylation in both hearts and cardiomyocytes, related to inhibition of protein phosphatase 1 activity. In a model of aortic banding-induced chronic pressure overload, heart function was similarly depressed in transgenic and wild-type mice. CONCLUSIONS: We identified a novel mechanism in which Nox2 modulates cardiomyocyte SR Ca(2+) uptake and contractile function through redox-regulated changes in phospholamban phosphorylation. This mechanism can drive increased contractility in the short term in disease states characterized by enhanced renin-angiotensin system activation.

Aqueous leaf extract of Averrhoa carambola L. (Oxalidaceae) reduces both the inotropic effect of BAY K 8644 on the guinea pig atrium and the calcium current on GH3cells / Extrato aquoso das folhas de Averrhoa carambola L. (Oxalidaceae) reduz tanto o efeito inotrópico do BAY K 8644 em átrio de cobaia, quanto a corrente de cálcio em células GH3

It was previously showed that aqueous leaf extract (AqEx) of Averrhoa carambola depresses the guinea pig atrial inotropism. Therefore, experiments were carried out on guineapig left atrium and on pituitary GH3 cells in order to evaluate the effect of AqEx on the cellular calcium infl ux. The atrium was mounted in an organ chamber (5 mL, Tyrode, 27 ± 0.1 °C, 95% O2, 5 % CO2), stretched to 10 mN, and paced at 2 Hz (0.5 ms, 400 V) and GH3 cells were submitted to a whole cell voltage clamp confi guration. In the atrium, the AqEx (1500 μg/mL) shifted to the right the concentration-effect curve of the positive inotropic effect produced by (±) BAY K 8644, an L-type calcium channel agonist. The AqEx increased EC50 (concentration required to promote 50% of the maximum effect) of the inotropic effect of BAY K 8644 from 7.8 ± 0.38 to 115.1 ± 0.44 nM (N = 3; p < 0.05). In GH3 cells assayed with 500 μg/mL of AqEx, the L-type calcium inward current declined 30 % (from 282 to 190 pA). Nevertheless, the extract did not change the voltage correspondent to the peak current. These data suggest that, at least in part, the negative inotropic effect of AqEx on the guinea pig atrium is due to a reduction of the L-type calcium current.

Em estudo prévio mostrou-se que o extrato aquoso das folhas de Averrhoacarambola (ExAq) reduziu o inotropismo atrial da cobaia. Por isso, este trabalho avaliou se o ExAq interfere com o infl uxo de cálcio através da membrana celular. A investigação foi conduzidaem átrio esquerdo de cobaia, montado em cuba (5 mL, Tyrode, 27 ± 0,1 °C, 95 % O2, 5 % CO2), estirado para uma tensão de repouso de 10 mN e submetido a uma estimulação de 2 Hz (0,5 ms, 400 V). O efeito do ExAq sobre a entrada de cálcio nas células foi avaliado em átrio de cobaia e em células GH3, estas submetidas a ‘patch clamp’ na confi guração ‘whole cell’. No átrio, o ExAq (1500 μg /mL) deslocou para direita a curva concentração-efeito do (±) BAY K 8644 (agonista dos canais de cálcio tipo-L), aumentando a CE50 (concentração capaz de produzir 50 % do efeito máximo) de 7,8 ± 0,38 para 115,1 ± 0,44 nM (N = 3, p < 0,05). Em células GH3, este extrato (500 μg /mL) reduziu de 282 para 190 pA (30 %) a corrente de cálcio, sem contudo alterar a voltagem de pico da curva desta corrente. Estes resultados mostram que, pelo menos em parte, o efeito inotrópico negativo do ExAq em átrio de cobaia se deve a uma diminuição do infl uxo de cálcio pelos canais tipo-L.

Complete atrioventricular block on isolated guinea pig heart induced by an aqueous fraction obtained from Psidium guajava L. leaf / Bloqueio atrioventricular completo em coração isolado de cobaia produzido por uma fração aquosa obtida das folhas de Psidium guajava L

This paper aimed to study the electrocardiographic effect produced by the aqueous fraction (AqF) obtained from the acetic extract of Psidium guajava L. leaf on the isolated guinea pig heart. Electrocardiographic records (ECG) were obtained on isolated hearts beating spontaneously or under regular electrical stimulation. The hearts were mounted in a constant flow Langendorff perfusion system. Until 20 mg/mL, AqF did not change the spontaneous cardiac rate (control: 180 ± 9 bpm, test: 182 ± 10 bpm; N = 3; p > 0.05). Concentrations equal or greater then 20 mg/mL induced complete atrioventricular block (AVB). However, this effect promptly disappeared when AqF was removed from the perfusion fluid (N = 3 hearts). The AVB induced by AqF involves heart muscarinic receptors because atropine sulfate (1.5 mM) could prevent the appearance of such disturbance.

O presente trabalho visou estudar o efeito eletrocardiográfico produzido pela fração aquosa (AqF) obtida do extrato acético das folhas de Psidium guajava L. em coração isolado de cobaia. Os traçados eletrocardiográficos foram obtidos em corações batendo espontaneamente ou então sob estimulação elétrica. Os corações foram montados em uma sistema de perfusão do tipo Langendoff de fluxo constante. A AqF, usada em concentrações menores que 20 mg/mL, não alterou a freqüência espontânea do coração (controle: 180 ± 9 bpm, teste: 182 ± 10 bpm; N = 3; p > 0,05). Todavia, concentrações iguais ou maiores que 20 mg/mL produziram bloqueio atrioventricular completo (BAV). Este efeito, contudo, desapareceu prontamente quando se removeu a AqF do fluido de perfusão coronariana (N = 3 corações). O BAV promovido pela AqF se faz mediado pelos receptores muscarínicos porque o sulfato de atropina (1,5 mM) impediu o aparecimento deste efeito.