Pegg W, Michalak M
Am J Physiol. 1987 Jan;252(1 Pt 2):H22-31. doi: 10.1152/ajpheart.1987.252.1.H22.
The composition and function of fetal and mature sheep cardiac sarcoplasmic reticulum membranes were investigated. Phospholamban, a major phosphoprotein in the mature sarcoplasmic reticulum membranes, was present in early stages of cardiac myogenesis. This fetal form of phospholamban was phosphorylated by cAMP-dependent protein kinase but not in the presence of Ca2+ and calmodulin. Ca2+ uptake and Ca2+-dependent ATPase activity were low in fetal sarcoplasmic reticulum compared with the adult controls, although the apparent affinities for Ca2+ were similar. Sarcoplasmic reticulum vesicles isolated at all developmental stages had very low levels of plasma membrane (as determined by Na+-K+-ATPase and Na+-Ca2+ exchanger activities) and mitochondrial contamination. Sarcoplasmic reticulum Ca2+ uptake and Ca2+-dependent ATPase activities were not affected by micromolar concentrations of vanadate, and the accumulated Ca2+ could not be released by the addition of NaCl. The amount of both the 110- and 55-kDa protein bands, identified with specific antibodies as Ca2+-ATPase and calsequestrin, respectively, was low in early stages of cardiac myogenesis. Age-related differences in the Ca2+ transport properties of cardiac sarcoplasmic reticulum and in the amount of the Ca2+-ATPase and calsequestrin may explain alterations in the regulation of intracellular Ca2+ concentrations in the fetal heart. This may contribute to the developmental changes in myocardial function.
研究了胎儿和成熟绵羊心肌肌浆网膜的组成和功能。受磷蛋白是成熟肌浆网膜中的一种主要磷蛋白，在心肌发生的早期阶段就已存在。这种胎儿形式的受磷蛋白可被环磷酸腺苷依赖性蛋白激酶磷酸化，但在有Ca2+和钙调蛋白存在时则不能。与成年对照组相比，胎儿肌浆网的Ca2+摄取和Ca2+依赖性ATP酶活性较低，尽管对Ca2+的表观亲和力相似。在所有发育阶段分离得到的肌浆网小泡的质膜水平（通过Na+-K+-ATP酶和Na+-Ca2+交换体活性测定）和线粒体污染程度都非常低。肌浆网Ca2+摄取和Ca2+依赖性ATP酶活性不受微摩尔浓度钒酸盐的影响，并且添加NaCl不能释放积累的Ca2+。分别用特异性抗体鉴定为Ca2+-ATP酶和肌集钙蛋白的110 kDa和55 kDa蛋白条带的量在心肌发生早期较低。心肌肌浆网Ca2+转运特性以及Ca2+-ATP酶和肌集钙蛋白量的年龄相关差异可能解释胎儿心脏细胞内Ca2+浓度调节的改变。这可能有助于心肌功能的发育变化。
