大鼠脑微粒体的钠依赖性和钙依赖性钙转运

Sodium-dependent and calcium-dependent calcium transport by rat brain microsomes.

作者信息

Schellenberg G D, Swanson P D

出版信息

Biochim Biophys Acta. 1981 Oct 20;648(1):13-27. doi: 10.1016/0005-2736(81)90120-6.

Abstract

Microsomal vesicles prepared from rat brain contain a Na+-Ca2+ exchange transport system capable of accumulating Ca2+ in a time- and temperature-dependent manner. The Ca2+ accumulated by these vesicles was released by the Ca2+ ionophore A23187 but not by EGTA. The Km value for Ca2+ uptake was 23 microM with a maximal velocity of 21 nmol Ca2+/mg per min. Ca2+ uptake was significantly inhibited by La3+, Sr2+, Mn2+ and Ba2+ and to a lesser extent by Mg2+. 45Ca2+ accumulated by Na+-dependent uptake could be released by 40Ca2+, indicating the presence of a Ca2+-Ca2+ exchange activity in the microsomes. Ca2+-Ca2+ exchange was stimulated in Li+- and K+-containing media as compared to choline+ media. Microsomes also catalyzed ATP-dependent Ca2+ uptake (in the absence of Na+ gradient). The Ca2+ sequestered by this mechanism could be released by extravesicular Na+, indicating that both the ATP-dependent and the Na+-dependent Ca2+ uptake systems are present in the same membrane. The microsomal preparation used did not contain measurable amounts of succinate dehydrogenase activity or oligomycin-azide-dinitrophenol sensitive ATP-dependent Ca2+ uptake. Thus, the Ca2+ accumulation observed was not due to contaminating mitochondria. The preparation was enriched for 5'-nucleotidase and (Na+ + K+)-ATPase (plasma membrane markers) as well as antimycin A-resistant NADPH-dependent cytochrome c reductase activity (an endoplasmic reticulum marker).

摘要

从大鼠脑制备的微粒体囊泡含有一种Na⁺-Ca²⁺交换转运系统，该系统能够以时间和温度依赖性方式积累Ca²⁺。这些囊泡积累的Ca²⁺可被Ca²⁺离子载体A23187释放，但不能被EGTA释放。Ca²⁺摄取的Km值为23微摩尔，最大速度为每分钟21纳摩尔Ca²⁺/毫克。La³⁺、Sr²⁺、Mn²⁺和Ba²⁺显著抑制Ca²⁺摄取，Mg²⁺的抑制作用较小。通过Na⁺依赖性摄取积累的⁴⁵Ca²⁺可被⁴⁰Ca²⁺释放，表明微粒体中存在Ca²⁺-Ca²⁺交换活性。与胆碱⁺培养基相比，含Li⁺和K⁺的培养基刺激了Ca²⁺-Ca²⁺交换。微粒体还催化了ATP依赖性Ca²⁺摄取（在没有Na⁺梯度的情况下）。通过这种机制螯合的Ca²⁺可被囊泡外的Na⁺释放，表明ATP依赖性和Na⁺依赖性Ca²⁺摄取系统存在于同一膜中。所使用的微粒体制备物不含可测量量的琥珀酸脱氢酶活性或对寡霉素-叠氮化物-二硝基苯酚敏感的ATP依赖性Ca²⁺摄取。因此，观察到的Ca²⁺积累不是由于污染的线粒体。该制备物富含5'-核苷酸酶和（Na⁺+K⁺）-ATP酶（质膜标记物）以及抗霉素A抗性的NADPH依赖性细胞色素c还原酶活性（内质网标记物）。