RESUMEN
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.
RESUMEN
L-tetrahydropalmatine (THP) & verapamil ( Ver ) antagonized CaCl2-induced positive chronotropic response in spontaneously beating right atria of guinea pig, and noncompetitively antagonized CaCl2 -& isoprenaline ( Iso ) -induced positive inotropic effects of the left atria electrically driven at 1.5 Hz & Iso-induced positive chronotro-pic effects of the right atria. THP & Ver had dose-dependent & frequency-dependent inhibitory effects on contraction of the left atria, and inversed the frequency-contraction curve from positive staircase into negative staircase,but had only slight inhibitory effects on postrest potentiation. The results suggest that THP, similar to Ver, has inhibitory effects on isolated guinea pig atria, which might be related to antagonizing Ca2+ via blockade of Ca2+ influx.
RESUMEN
In the isolated perfused rat heart, TFH counteracted significantly the arrhythmias caused by perfusing with a solution without oxygen; increased ventricular fibrillation threshold markedly and showed a good dose-effective relation; prolonged the P-R period of electrocardiogram and decreased the heart rate and fell the amplitude of cardiac contraction markedly; and counteracted significantly the decrease of the heart rate and the amplitude of cardiac contraction caused by perfusing with a solution without oxygen. In the isolated guinea pig left atrium, TFH prolonged the function refractory period slightly. In the isolated guinea pig right atrium, TFH increased the accumulated dose of aconitine inducing arrhythmias.