Resposta inotropica a catecolaminas em miocitos ventriculares isolados de ratos submetidos a choque nas patas / Inotropic esponsiveness to catecholamines in ventricular myocytes isolated from footshock-stressed rats

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Supersensitivity to isoproterenol (ISO) chronotropic effect has been described in right atria from footshock-stressed rats, but information on inotropic responsiveness, particularly of the ventricles, is scarce. The goal of this study was to analyze the inotropic and pro-arrhythmic effect of catecholamines on left ventricular myocytes from footshockstressed rats, in comparison with cells from control animals. Adult male Wistar rats were submitted to 30-min long daily footshock sessions for 3 days. Peak cell shortening and the rate of spontaneous contractions during rest were measured in myocytes at 23 oC. Concentration-effect curves were obtained for noradrenaline (NA), ISO, 3-isobutyl-1- methylxanthine (IBMX) e CaCl2, for estimation of the following parameters Rmax (maximum response) and pD2 (-log of the agonist molar concentration that evokes halfmaximum response). The _ adrenoceptor (AR) population was analyzed by the Schild?s method. In the footshock group, Rmax values to NA and ISO were decreased. This difference was unaffected by _1AR blockade, but was abolished by blockade of _1AR (which increased Rmax to ISO in the footshock group only) or _2-AR (which decreased Rmax to ISO solely in the control group). Metoprolol pA2 value and the inotropic responsiveness to IBMX and CaCl2 were similar in both groups. Cells from footshockstressed rats were more responsive to NA and ISO pro-arrhythmic action. All procedures that abolished the difference in inotropic response between footshock and control groups also diminished the differences in arrhythmic responses. These results indicate that the inotropic hyporesponsiveness to catecholamines in the footshock group may be the result of increased spontaneous activity induced by these agonists. We conclude that footshock stress enhances catecholamine pro-arrhythmic effect in rat ventricular myocytes, while simultaneously decreases the inotropic apparent efficacy of these agonists

ASSUNTO(S)

inotropic activity stress (physiology) atividade inotropica stress (fisiologia) arrhythmima arritmia catecolaminas catecholamines

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