Asayama J, Tatsumi T, Miyazaki H, Omori I, Inoue D, Nakagawa M
Second Department of Medicine, Kyoto Prefectural University of Medicine, Japan.
Jpn Circ J. 1990 Feb;54(2):207-13. doi: 10.1253/jcj.54.207.
It is well known that the strength of postextrasystolic potentiation (PESP) is dependent on the prematurity of the ectopic beat, though the fundamental mechanism of the potentiation is still obscure. In this study, the effect of a resting interval on the strength of PESP was investigated in isolated papillary muscles of guinea pigs in the presence or absence of caffeine, which inhibits the functions of sarcoplasmic reticulum (SR). PESP of a fixed coupling interval increased and then decreased as the resting interval was prolonged. The maximum of PESP was obtained at a resting interval of 3 to 4 sec. The dependency of PESP on a coupling interval was decreased considerably by 5 x 10(-4) M caffeine and removed completely by 10(-2) M caffeine. Although 5 x 10(-4) M caffeine decreased the degree of contraction of postextrasystole, the maximum contraction of postextrasystole was still obtained at a resting interval of 3 to 4 sec. After the application of 10(-2) M caffeine, the postextrasystolic contraction gradually declined as the resting interval was prolonged. We conclude that SR Ca release contributes largely to a mechanism of PESP and increases in contribution as the coupling interval of an extrastimulation shortens, and that the optimal resting interval is determined by a balance between the activity of SR function and the activity of the sarcolemmal Ca extrusion mechanism.
众所周知，期外收缩后增强（PESP）的强度取决于异位搏动的提前程度，尽管这种增强的基本机制仍不清楚。在本研究中，在有或没有咖啡因（抑制肌浆网（SR）功能）存在的情况下，研究了静息间隔对豚鼠离体乳头肌中PESP强度的影响。随着静息间隔延长，固定耦合间隔的PESP先增加后降低。在3至4秒的静息间隔时获得PESP的最大值。5×10（-4）M咖啡因可使PESP对耦合间隔的依赖性显著降低，而10（-2）M咖啡因可使其完全消除。虽然5×10（-4）M咖啡因降低了期外收缩后的收缩程度，但在3至4秒的静息间隔时仍可获得期外收缩后的最大收缩。应用10（-2）M咖啡因后，随着静息间隔延长，期外收缩后的收缩逐渐下降。我们得出结论，SR钙释放对PESP机制有很大贡献，并且随着额外刺激的耦合间隔缩短，其贡献增加，并且最佳静息间隔由SR功能活性和肌膜钙外排机制活性之间的平衡决定。
