异丙肾上腺素对心肌细胞内钙释放和肌浆网内钙容量的影响

Effects of isoprenaline on intracellular Ca^(2+) release and sarcoplasmic reticulum Ca^(2+) content

目的 :心肌细胞膜上的 β-肾上腺素受体的激活对兴奋 -收缩耦联 (ECC)过程有重要的调节作用。本课题利用异丙肾上腺素 (ISO,1μmol/ L)激活 β-肾上腺素受体从而研究其对源自心肌细胞肌浆网的胞内钙释放 (ECC的重要环节 )和肌浆网内钙容量的影响 ,进而分析钙释放与钙容量之间的关系。方法 :局部场刺激作用于成年大鼠心肌细胞 ,促使后者产生动作电位 ,进而诱发胞内钙瞬变 (ACT) ,由 ACT可估测胞内钙释放。肌浆网内钙容量则由咖啡因 (2 0 m mol/ L)诱发的钙瞬变 (CCT)估测。实验结果均由 Zeiss L SM- 5 10激光共聚焦显微镜系统记录。结果 :ISO作用下的 ACT峰值为 10 .2 9± 0 .35 (n=13)比正常情况下的 5 .74± 0 .2 7(n=18)高 (P<0 .0 1)。 ISO作用下的CCT峰值为 11.2 3± 0 .2 9(n=13)比正常情况下的 7.6 2± 0 .2 4 (n=18)高 (P<0 .0 1)。结论 :ISO可明显地提高心肌细胞内钙释放量和肌浆网内的钙容量。不管有无 ISO存在 ,胞内钙释放量总是只占肌浆网内钙容量的一部分。在正常情况下 ,心肌的钙释放量有较大的储备能力 ,且此储备可因β-肾上腺素受体的激活而动员。

AIM: β-Adrenergic receptor stimulation exerts important regulation on cardiac excitation-contraction coupling. In this study, isoprenaline (ISO, 1 μmol/L) were employed as β-Adrenergic receptor stimulator to investigate its effects on SR Ca 2+ content and SR Ca 2+ release (which is the key process in excitation-contraction coupling.), and the relationship between them. METHODS: Local field stimulation was delivered to freshly isolated rat single cardiac myocytes to generate action-potential-induced Ca 2+ transients (ACT) for assessing intracellular Ca 2+ release. Caffeine (20 mmol/L)-induced Ca 2+ transients (CCT) were used to estimate SR Ca 2+ content. Results were recorded by confocal Ca 2+ imaging with a Zeiss LSM-510 confocal microscopic system. RESULTS: The peak of ACT with ISO was greater than that under the control conditions (P<0.01) (in ΔF/F 0, the normalized fluorescence, where F 0 denotes the resting fluorescence): 10.29±0.35 (n=13) versus 5.74±0.27 (n=18). And the peak of CCT with ISO was greater than that under the control conditions (P<0.01) as well: 11.23±0.29 (n=13) versus 7.62±0.24 (n=18). CONCLUSION: ISO increased both cardiac intracellular Ca 2+ release and SR Ca 2+ content greatly. Ca 2+ release was always only a part of the releasable SR Ca 2+ content, regardless the presence of ISO. Under the normal conditions, cardiac myocytes had great reserve for Ca 2+ release, which could be activated by β-Adrenergic receptor stimulation.