Asayama J, Tatsumi T, Omori I, Inoue D, Katsume H, Nakagawa M
Second Department of Medicine, Kyoto Prefectural University of Medicine, Japan.
Jpn Circ J. 1989 Apr;53(4):319-28. doi: 10.1253/jcj.53.319.
We studied the combined effects of hypoxia and the absence of glucose on postextrasystolic potentiated and resting contractions in papillary muscle of guinea pigs. Postextrasystolic potentiations (PESPs) were evoked following trains of 40 externally applied continuous stimulations. During hypoxia resting (regular) contractions decreased to about 25% of baseline tension at 30 degrees C, whereas postextrasystolic potentiated contractions decreased to about 35% of baseline measurement of postextrasystolic potentiated contraction. In contrast, with reoxygenation, PESPs recovered quickly while resting contractions recovered gradually. Caffeine abolished the potentiation of post-extrasystolic contraction not only in normoxia but also in hypoxia. We speculate that calcium release from the sarcoplasmic reticulum (SR) is attributable to PESP for the most part, and that the trans-sarcolemmal calcium influx generally contributes to the steady-state tensions developed by continuous stimulations. In addition, it seems that PESP works in a ischemic heart to compensate for the decreased tension during hypoxia as a potentiation by a premature ventricular contraction. Trans-sarcolemmal calcium influx might be affected more easily than the SR calcium release, by a combination of hypoxia and the absence of glucose, that is, the sarcolemma may be more susceptible to hypoxic injury than the SR.
我们研究了缺氧和无糖状态对豚鼠乳头肌期外收缩后增强收缩和静息收缩的联合作用。在施加40次外部连续刺激的序列后诱发期外收缩后增强（PESP）。在缺氧期间，静息（常规）收缩在30℃时降至基线张力的约25%，而期外收缩后增强收缩降至期外收缩后增强收缩基线测量值的约35%。相比之下，复氧后，PESP迅速恢复，而静息收缩逐渐恢复。咖啡因不仅在常氧状态下，而且在缺氧状态下都消除了期外收缩后的增强作用。我们推测，肌浆网（SR）释放钙在很大程度上归因于PESP，而跨肌膜钙内流通常有助于连续刺激产生的稳态张力。此外，似乎PESP在缺血心脏中起作用，作为室性早搏的一种增强作用来补偿缺氧期间张力的降低。跨肌膜钙内流可能比SR钙释放更容易受到缺氧和无糖状态联合作用的影响，也就是说，肌膜可能比SR更容易受到缺氧损伤。
