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BmKⅠ,an α-like scorpion neurotoxin,specifically modulates isolated rat cardiac mechanical and electrical activity

Sun Haiying, Zhu Haifeng, Ji Yonghua

Institute of Physiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. Shanghai 200031,China

Abstract

In this study, cardiotonic and cardiotoxic effects of Buthus martensi Karsch (BmK)Ⅰ, a modulator of voltage-gated sodium channels, were investigated on the isolated rat hearts. The results showed that BmKⅠ evoked complex effects characterized by a change in both cardiac mechanical and electrical activity. Langendorff perfusion showed that: ( 1 ) maximal left ventricular developed pressure (LVDPmax) and dp/dtmax were markedly increased by BmKⅠ (0.5 -10 mol/L) in a dose-dependent manner (n =6, P＜0.05), positive chronotropic effects were also induced by BmKⅠ (n=6, P＜0.05); (2) negative inotropic action and bradycardia could be elicited at a larger dose of BmKⅠ(20μ mol/L); (3) the coronary flow varied inversely with the positive inotropic effects, coronary flow reduced during positive inotropic effects from 14. 5 to 8. 6 ml/min after administration of 500 nmol/L BmKⅠ ( n = 6, P＜ 0. 05). In addition, tachycardia and complex cardiac arrhythmias were induced by BmKⅠ (0.5-10 moL/L). The modulating of BmKⅠon the heart mechanical, electrical activity could be partially recovered after washing. As propranolol was applied to block the release of catecholamines before administration of BmKⅠ, suggesting that the changes in cardiac mechanical and electrical activity induced by BmKⅠ might not due to catecholamine release from the nerve terminal and subsequent stimulation of theβ-adrenoceptor but attributable to the modulation of BmKⅠon cardiac voltage-gated sodium channels.

Key words: Inotropic effect;Electrocardiogram (ECG);;

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Citing This Article：

Sun Haiying, Zhu Haifeng, Ji Yonghua. BmKⅠ,an α-like scorpion neurotoxin,specifically modulates isolated rat cardiac mechanical and electrical activity. Acta Physiol Sin 2003; 55 (5): (in Chinese with English abstract).