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2,3,7,8-tetrachlorodibenzo-p-dioxin increases cardiac myocyte intracellular calcium and progressively impairs ventricular contractile responses to isoproterenol and to calcium in chick embryo hearts.

Abstract：

:Binding by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the Ah receptor leads to transcriptional activation of several genes and a toxicity syndrome that includes tumor promotion, wasting, hormonal and immune system dysfunction, and death. Recent findings indicate that TCDD may also affect cardiac function. Here, we used the chick embryo, a TCDD-sensitive species, to further characterize the effects of TCDD on ventricular muscle contraction and on cardiac myocyte [Ca2+]i assessed with fura 2. The results show that TCDD causes an evolving sequence of contractile defects, independent of changes in diet, first impairing cAMP-modulated contraction (after 48 hr) and later (by seven days) decreasing responses to [Ca2+]o. Phenobarbital, even at high doses, failed to affect the inotropic response to isoproterenol, supporting the specificity of the ventricular contractile effects of TCDD. TCDD treatment also depressed inotropic responses to theophylline and forskolin, indicating that it has a post-beta-adrenergic receptor effect on cAMP action. In contrast to its depression of responses to beta-adrenergic stimuli and to [Ca2+]o, TCDD did not affect initial tensions of ventricular muscle stimulated at 1 Hz or the force-frequency response up to 1 Hz, indicating that TCDD-treated ventricles can respond normally at slow rates of stimulation. TCDD treatment depressed lusitropic (relaxation) responses to isoproterenol and to increasing [Ca2+]o indicating that it impairs the ability of the sarcoplasmic reticulum to sequester Ca2+. Fura 2-based measurements showed that [Ca2+]i was nearly doubled after TCDD treatment. The increase in [Ca2+]i is consistent with the decrease in the contractile response to [Ca2+]o, amelioration of the response to isoproterenol by subphysiologic concentrations of [Ca2+]o, and intermittent lack of response to electrical stimulation in high K+ observed in ventricles from TCDD-treated embryos. TCDD treatment also depressed the initial increase in [Ca2+]i by isoproterenol, consistent with the decreased contractile response to isoproterenol. The findings show that TCDD causes well defined, progressive impairment of avian ventricular responses to inotropic stimuli, providing new evidence that the heart is a target of TCDD action and that TCDD disturbs intracellular calcium processing.

journal_name

Mol Pharmacol

journal_title

Molecular pharmacology

authors

Canga L,Paroli L,Blanck TJ,Silver RB,Rifkind AB

subject

Has Abstract

pub_date

1993-12-01 00:00:00

pages

1142-51

issue

eissn

0026-895X

issn

1521-0111

journal_volume

pub_type

杂志文章

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2,3,7,8-tetrachlorodibenzo-p-dioxin increases cardiac myocyte intracellular calcium and progressively impairs ventricular contractile responses to isoproterenol and to calcium in chick embryo hearts.