Lee Y H, Park B G, Ahn D S, Kang B S
Department of Physiology, Yonsei University College of Medicine, Seoul, Korea.
Yonsei Med J. 1996 Feb;37(1):38-46. doi: 10.3349/ymj.1996.37.1.38.
To elucidate the Ca2+ release mechanisms in the rabbit coronary artery, arterial preparations were permeabilized with beta-escin and changes in tension were measured under varying experimental conditions. Additionally, we investigated properties and distribution of two kinds of Ca2+ release mechanisms, Ca2+-induced Ca2+ release (CICR) and IP3-induced Ca2+ release (IICR). The results obtained were summarized as follows; 1. When a rabbit coronary artery was incubated in a relaxing solution containing 30 microM beta-escin for 40 min. sensitivity to externally added Ca2+ was much higher in beta-escin permeabilized muscle than in intact preparations. The contractile effect of IP3 in beta-escin permeabilized muscle was also demonstrated; 2. Caffeine and IP3 contracted coronary arteries were permeabilized with beta-escin, but the amplitude of contraction was much larger in the presence of caffeine than of IP3. 3. Intracellular heparin completely inhibited the contractions induced by IP3, but not those by caffeine. On the other hand, procaine inhibited the responses to caffeine, but not those to IP3. Ryanodine inhibited both the caffeine- and IP3-induced contractions. 4. The amplitude of contractile responses was much larger to the maximal stimulation of CICR by applying caffeine than to the maximal stimulation of IICR by applying IP3. After the maximal CICR stimulation by caffeine, the activation of IICR by IP3 without the reloading of Ca2+ could no longer evoke contraction. On the other hand, after the maximal IICR activation, the activation of CICR could still evoke contraction although the amplitude of the contraction was smaller when compared with the case without the initial IICR stimulation. 5. Acetylcholine contracted coronary artery smooth muscles were permeabilized with beta-escin. However, in the absence of added guanosine triphosphate (GTP), the responses were very small. Acetylcholine-induced contraction was inhibited by heparin, but not by procaine. From the above results, it may be concluded that there are two kinds of mechanisms of Ca2+ release, CICR and IICR, in the rabbit coronary artery smooth muscle cell. Also, whereas the CICR mechanism distributes on the membrane of the whole smooth muscle Ca2+ store, the IICR mechanism distributes only on a part of it.
为阐明兔冠状动脉中的Ca2+释放机制，用β-七叶皂苷使动脉标本通透化，并在不同实验条件下测量张力变化。此外，我们研究了两种Ca2+释放机制，即Ca2+诱导的Ca2+释放（CICR）和IP3诱导的Ca2+释放（IICR）的特性和分布。所得结果总结如下：1. 将兔冠状动脉在含有30 microM β-七叶皂苷的舒张溶液中孵育40分钟后，β-七叶皂苷通透化的肌肉对外部添加的Ca2+的敏感性远高于完整标本。还证实了IP3在β-七叶皂苷通透化肌肉中的收缩作用；2. 咖啡因和IP3使经β-七叶皂苷通透化的冠状动脉收缩，但在咖啡因存在下收缩幅度远大于IP3存在时。3. 细胞内肝素完全抑制IP3诱导的收缩，但不抑制咖啡因诱导的收缩。另一方面，普鲁卡因抑制对咖啡因的反应，但不抑制对IP3的反应。Ryanodine抑制咖啡因和IP3诱导的收缩。4. 应用咖啡因对CICR进行最大刺激时的收缩反应幅度远大于应用IP3对IICR进行最大刺激时的幅度。在咖啡因对CICR进行最大刺激后，IP3在不重新加载Ca2+的情况下激活IICR不再能引起收缩。另一方面，在IICR最大激活后，CICR的激活仍能引起收缩，尽管与未进行初始IICR刺激的情况相比收缩幅度较小。5. 乙酰胆碱使经β-七叶皂苷通透化的冠状动脉平滑肌收缩。然而，在未添加鸟苷三磷酸（GTP）的情况下，反应非常小。乙酰胆碱诱导的收缩被肝素抑制，但不被普鲁卡因抑制。从上述结果可以得出结论，兔冠状动脉平滑肌细胞中存在两种Ca2+释放机制，即CICR和IICR。此外，CICR机制分布在整个平滑肌Ca2+储存膜上，而IICR机制仅分布在其中一部分上。
