Kosterin S A, Bratkova N F, Kurskiĭ M D
Biokhimiia. 1985 Aug;50(8):1350-61.
Using atomic absorption spectroscopy, it was shown that the amount of firmly bound Ca2+ in cattle mitochondria and myometrium sarcolemma is 160 +/- 10 and 30 +/- 10 mumol/kg of wet tissue, respectively. The Ca2+ 1 accumulating capacity of mitochondria (350 nmol per mg of protein) markedly exceeds that of sarcolemmal vesicles (30 nmol per mg of protein). Using a Ca2+-EGTA buffer, it was found that the affinity of ionized Ca for the mitochondrial transport system (Km = 5.69 microM) is higher than that for the Na+-Ca2+ system of sarcolemma exchange (Km = 30 microM), but is markedly lower than that for the Mg2+, ATP-dependent Ca2+ efflux (Km = 0.35 microM). A kinetic analysis demonstrated that the sarcolemmal Ca2+ pump is incapable of causing complete relaxation of the smooth muscle within the physiologically significant time, whereas the Ca2+ transport system of mitochondria evokes this process within 21 s. However, the contribution of the Ca2+ pump to the regulation of the Ca2+ content in myocytes is paralleled with the accumulation of Ca2+ in mitochondria and is realized at low concentrations of this cation in the myoplasm, i.e., at late steps of relaxation. A mechanism of Ca2+ control over myometrium relaxation is proposed. The system of non-electrogenic Na+-Ca2+ exchange maintains Ca2+ concentration in the myoplasm as high as 10(-5) M. Mitochondria which accumulate the bulk of Ca2+ rapidly decrease its concentration in the cytoplasm down to 10(-6)-10(-7) M; at these values, the activity of the sarcolemmal Ca2+ pump with a high affinity for the transfer substrate is manifested. In this way, the Ca2+ pump accomplishes fine regulation of Ca2+ concentration in the myocytes.
利用原子吸收光谱法表明，牛线粒体和子宫肌层肌膜中牢固结合的Ca2+量分别为每千克湿组织160±10和30±10μmol。线粒体的Ca2+积累能力（每毫克蛋白质350 nmol）明显超过肌膜囊泡（每毫克蛋白质30 nmol）。使用Ca2+-EGTA缓冲液发现，离子化Ca对线粒体转运系统的亲和力（Km = 5.69μM）高于对肌膜交换的Na+-Ca2+系统的亲和力（Km = 30μM），但明显低于对Mg2+、ATP依赖性Ca2+外流的亲和力（Km = 0.35μM）。动力学分析表明，肌膜Ca2+泵在生理上显著的时间内无法使平滑肌完全松弛，而线粒体的Ca2+转运系统在21秒内引发该过程。然而，Ca2+泵对心肌细胞中Ca2+含量调节的贡献与线粒体中Ca2+的积累平行，并在肌浆中该阳离子浓度较低时实现，即在松弛的后期步骤。提出了Ca2+控制子宫肌层松弛的机制。非电生性Na+-Ca2+交换系统将肌浆中的Ca2+浓度维持在高达10(-5) M。积累大部分Ca2+的线粒体迅速将其在细胞质中的浓度降低至10(-6)-10(-7) M；在这些值下，对转运底物具有高亲和力的肌膜Ca2+泵的活性得以体现。通过这种方式，Ca2+泵实现了对心肌细胞中Ca2+浓度的精细调节。
