Michalak M
Department of Pediatrics, University of Alberta, Edmonton, Canada.
Biochem J. 1988 Aug 1;253(3):631-6. doi: 10.1042/bj2530631.
Ca2+-induced Ca2+ release and pH-induced Ca2+ release activities were identified in sarcoplasmic-reticulum (SR) vesicles isolated from adult- and fetal-sheep hearts. Ca2+-induced Ca2+ release and pH-induced Ca2+ release appear to proceed via the same channels, since both phenomena are similarly inhibited by Ruthenium Red. Ca2+ release from fetal SR vesicles is inhibited by higher concentrations of Ruthenium Red than is that from adult membranes. Both fetal and adult SR vesicles bind ryanodine. Fetal SR shows higher ryanodine-binding capacity than adult SR vesicles. Scatchard analysis of ryanodine binding revealed only one high-affinity binding site (Kd 6.7 nM) in fetal SR vesicles compared with two distinct binding sites (Kd 6.6 and 81.5 nM) in the adult SR vesicles. SR vesicles isolated from fetal and adult hearts were separated on discontinuous sucrose gradients into light (free) and heavy (junctional) SR vesicles. Heavy SR vesicles isolated from adult hearts exhibited most of the Ca2+ release activities. In contrast, Ca2+-induced Ca2+ release, pH-induced Ca2+ release and ryanodine receptors were detected in both light and heavy fetal SR. These results suggest that fetal SR may not be morphologically and functionally as well differentiated as that of adult cardiac muscle and that it may contain a greater number of Ca2+-release channels than that present in adult SR membranes.
在从成年和胎儿绵羊心脏分离出的肌浆网（SR）囊泡中鉴定出了Ca2+诱导的Ca2+释放和pH诱导的Ca2+释放活性。Ca2+诱导的Ca2+释放和pH诱导的Ca2+释放似乎通过相同的通道进行，因为这两种现象都受到钌红的类似抑制。与成年膜相比，更高浓度的钌红可抑制胎儿SR囊泡中的Ca2+释放。胎儿和成年SR囊泡均结合兰尼碱。胎儿SR显示出比成年SR囊泡更高的兰尼碱结合能力。对兰尼碱结合的Scatchard分析显示，胎儿SR囊泡中只有一个高亲和力结合位点（Kd 6.7 nM），而成年SR囊泡中有两个不同的结合位点（Kd 6.6和81.5 nM）。从胎儿和成年心脏分离出的SR囊泡在不连续蔗糖梯度上分离为轻（游离）和重（连接）SR囊泡。从成年心脏分离出的重SR囊泡表现出大部分Ca2+释放活性。相比之下，在轻和重的胎儿SR中均检测到Ca2+诱导的Ca2+释放、pH诱导的Ca2+释放和兰尼碱受体。这些结果表明，胎儿SR在形态和功能上可能不如成年心肌那样分化良好，并且其可能比成年SR膜中存在的Ca2+释放通道数量更多。
