A DIMINISHED ROLE FOR THE SARCOPLASMIC-RETICULUM IN NEWBORN MYOCARDIAL-CONTRACTION - EFFECTS OF RYANODINE
A DIMINISHED ROLE FOR THE SARCOPLASMIC-RETICULUM IN NEWBORN MYOCARDIAL-CONTRACTION - EFFECTS OF RYANODINE
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DOI：
10.1203/00006450-198908000-00005
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发表时间：
1989-08-01
影响因子：
3.6
通讯作者：
FRIEDMAN, WF
中科院分区：
文献类型：
--
作者：
KLITZNER, TS;FRIEDMAN, WF
Ryanodine 已知可减少肌浆网 (SR) 的 Ca2+ 释放，与单蔗糖间隙电压钳技术结合使用，研究从新生和成年兔子分离的乳头肌中的兴奋-收缩耦合。 Ryanodine 改变了成人中电压钳引起的张力的组成部分，产生了与正常新生儿非常相似的模式。兰尼定显着且显着地降低了成熟心肌张力的相位成分。此外，兰尼定显着改变了该张力成分的电压依赖性，表明其产生机制发生了变化。紧张的显着阶段性成分的出现，通常不存在，但在新生儿中通过 Ca2+ 负荷产生，也被兰尼定消除。这些结果支持了先前的观点，即哺乳动物心肌中电压钳引起的张力的相位成分是由 SR 中 Ca2+ 的释放产生的。在新生儿中，兰尼碱引起的相性张力与强直性张力之比的下降幅度明显小于成人，这表明 SR 在较年轻的年龄组中兴奋-收缩耦合中的作用要小得多。尽管兰尼碱对相张力有显着影响，但在新生儿或成人心脏中，跨膜 Ca2+ 内流产生的强直张力的幅度或电压依赖性没有变化。这项研究表明，在新生心肌中，SR 释放的 Ca2+ 在兴奋-收缩耦合中的作用可以忽略不计，而这取决于 Ca2+ 从细胞外空间的流入。
Ryanodine, known to reduce Ca2+ release from the sarcoplasmic reticulum (SR), was used in conjunction with the single sucrose gap voltage clamp technique to study excitation-contraction coupling in papillary muscles isolated from newborn and adult rabbits. Ryanodine altered the components of voltage clamp-induced tension in the adult producing a pattern that closely resembled the normal newborn. The phasic component of tension in mature myocardium was markedly and significantly reduced by ryanodine. In addition, ryanodine significantly altered the voltage dependence of this component of tension, suggesting a change in its mechanism of generation. The appearance of a prominent phasic component of tension, absent normally, but produced in the newborn by Ca2+ loading, was also abolished by ryanodine. These results support previous proposals that the phasic component of voltage clamp-induced tension in mammalian myocardium is produced by the release of Ca2+ from the SR. In the newborn, ryanodine caused a significantly smaller decrease in the ratio of phasic to tonic tension than in the adult, suggesting a much less significant role for the SR in excitation-contraction coupling in the younger age group. Although ryanodine had a significant effect on phasic tension, no alteration in the amplitude or voltage dependence of tonic tension, generated by transmembrane Ca2+ influx, could be demonstrated in either newborn or adult heart. This investigation suggests that in newborn myocardium, Ca2+ release from the SR plays a negligible role in excitation-contraction coupling, which depends, rather, on the influx of Ca2+ from the extracellular space.