Campbell Anthony K, Wann Kenneth T, Matthews Stephanie B
Department of Medical Biochemistry and Immunology, Wales College of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK.
Comp Biochem Physiol B Biochem Mol Biol. 2004 Oct;139(2):225-34. doi: 10.1016/j.cbpc.2004.07.004.
The cladoceran Daphnia pulex is well established as a model for ecotoxicology. Here, we show that D. pulex is also useful for investigating the effects of toxins on the heart in situ and the toxic effects in lactose intolerance. The mean heart rate at 10 degrees C was 195.9+/-27.0 beats/min (n=276, range 89.2-249.2, >80% 170-230 beats/min). D. pulex heart responded to caffeine, isoproteronol, adrenaline, propranolol and carbachol in the bathing medium. Lactose (50-200 mM) inhibited the heart rate by 30-100% (K(1/2)=60 mM) and generated severe arrhythmia within 60 min. These effects were fully reversible by 3-4 h. Sucrose (100-200 mM) also inhibited the heart rate, but glucose (100-200 mM) and galactose (100-200 mM) had no effect, suggesting that the inhibition by lactose or sucrose was not simply an osmotic effect. The potent antibiotic ampicillin did not prevent the lactose inhibition, and two diols known to be generated by bacteria under anaerobic conditions were also without effect. The lack of effect of l-ribose (2 mM), a potent inhibitor of beta-galactosidase, supported the hypothesis that lactose and other disaccharides may affect directly ion channels in the heart. The results show that D. pulex is a novel model system for studying effects of agonists and toxins on cell signalling and ion channels in situ.
枝角类的大型蚤已被确立为生态毒理学的模型。在此，我们表明大型蚤对于研究毒素对原位心脏的影响以及乳糖不耐受中的毒性作用也很有用。10摄氏度时的平均心率为195.9±27.0次/分钟（n = 276，范围89.2 - 249.2，>80%在170 - 230次/分钟之间）。大型蚤的心脏对浴液中的咖啡因、异丙肾上腺素、肾上腺素、普萘洛尔和卡巴胆碱有反应。乳糖（50 - 200 mM）使心率降低30 - 100%（半数抑制浓度K(1/2)=60 mM），并在60分钟内产生严重心律失常。这些作用在3 - 4小时内完全可逆。蔗糖（100 - 200 mM）也能抑制心率，但葡萄糖（100 - 200 mM）和半乳糖（100 - 200 mM）没有影响，这表明乳糖或蔗糖的抑制作用并非仅仅是渗透效应。强效抗生素氨苄青霉素不能阻止乳糖的抑制作用，已知在厌氧条件下由细菌产生的两种二醇也没有作用。β-半乳糖苷酶的强效抑制剂l-核糖（2 mM）没有效果，这支持了乳糖和其他二糖可能直接影响心脏离子通道的假说。结果表明，大型蚤是研究激动剂和毒素对原位细胞信号传导和离子通道影响的新型模型系统。
