Ondrias K, Borgatta L, Kim D H, Ehrlich B E
Department of Medicine, University of Connecticut, Farmington 06030.
Circ Res. 1990 Nov;67(5):1167-74. doi: 10.1161/01.res.67.5.1167.
To define the mechanism of doxorubicin cardiotoxicity, the effects of doxorubicin and caffeine were examined on calcium release channels from cardiac sarcoplasmic reticulum. We found that calcium release from cardiac sarcoplasmic reticulum vesicles was induced by both compounds. When sarcoplasmic reticulum vesicles were incorporated into planar lipid bilayers, calcium-permeable channels were observed. Addition of caffeine (2.5-10 mM) increased channel open probability from less than 0.1% to 40%, and this effect persisted for a mean of 44 minutes. In contrast, doxorubicin (2.5-10 microM) had a biphasic effect; initially, doxorubicin activated the channel, whereas after a mean of 8 minutes, the channel became irreversibly inhibited. Although the degree of channel activation by doxorubicin was concentration dependent, the time needed to inactivate the channel was concentration independent. Pretreatment with dithiothreitol (0.2 mM) prevented doxorubicin-induced channel inactivation, and channel activity persisted for an average of 58 minutes. Dithiothreitol alone did not alter channel open probability. Our results support the hypotheses that 1) the integrity of sulfhydryl groups is important for some aspects of calcium release channel function and 2) activation and inactivation of the channel are separable processes. The biphasic effect of doxorubicin on channel function may also correspond to the clinically observed adverse effects of doxorubicin, a widely used chemotherapeutic agent that, after prolonged usage, causes a dilated cardiomyopathy.
为了明确阿霉素心脏毒性的机制，研究了阿霉素和咖啡因对心肌肌浆网钙释放通道的影响。我们发现这两种化合物均可诱导心肌肌浆网囊泡释放钙。当将肌浆网囊泡整合到平面脂质双分子层中时，可观察到钙通透性通道。加入咖啡因（2.5 - 10 mM）可使通道开放概率从低于0.1%增加到40%，且这种作用平均持续44分钟。相比之下，阿霉素（2.5 - 10 μM）具有双相效应；最初，阿霉素激活通道，而平均8分钟后，通道被不可逆地抑制。尽管阿霉素对通道的激活程度呈浓度依赖性，但使通道失活所需的时间与浓度无关。用二硫苏糖醇（0.2 mM）预处理可防止阿霉素诱导的通道失活，通道活性平均持续58分钟。单独使用二硫苏糖醇不会改变通道开放概率。我们的结果支持以下假设：1）巯基的完整性对钙释放通道功能的某些方面很重要；2）通道的激活和失活是可分离的过程。阿霉素对通道功能的双相效应也可能与临床上观察到的阿霉素的不良反应相对应，阿霉素是一种广泛使用的化疗药物，长期使用后会导致扩张型心肌病。
