Fry C H, Harding D P, Miller D J
Sherrington School of Physiology, St Thomas's Hospital Medical School, London, U.K.
Proc R Soc Lond B Biol Sci. 1989 Feb 22;236(1282):53-77. doi: 10.1098/rspb.1989.0012.
Ca2+ exchange has been measured in a suspension of rat ventricular myocytes treated with digitonin or saponin to render the sarcolemma permeable to small molecules and ions. Two fractions of exchange were identified, one that was attributed to the mitochondrial component of the cell and the other to a non-mitochondrial fraction. Mitochondrial Ca2+ uptake was blocked by sodium azide and depended on respiratory substrates whereas non-mitochondrial uptake occurred independently of these molecules but was dependent on ATP and creatine phosphate. Non-mitochondrial Ca2+ uptake could be induced at a Ca2+ concentration below 1 microM and the initial rate increased with concentration up to 100 microM. Uptake could be reversed by sulmazole (a caffeine-like substance) and this reversal in turn inhibited by ryanodine. These properties suggest that the major locus for non-mitochondrial Ca2+ exchange is at the sarcoplasmic reticulum. Ca2+ exchange could be modulated by a number of agents, including carnosine, but was unaffected by others, including Na+, inositol trisphosphate and cyclic AMP. A kinetic model of the data is presented, which incorporates similar data of Ca2+ uptake into the mitochondrial fraction. The rates of Ca2+ exchange measured in these experiments suggest that these two components of the cell can reduce the sarcoplasmic Ca2+ concentration rapidly enough to account for the observed transient nature of the isometric twitch. Furthermore, it is suggested that both non-mitochondrial and mitochondrial fractions of the cell could significantly contribute to tension relaxation in rat cardiac muscle.
在经洋地黄皂苷或皂角苷处理以使肌膜对小分子和离子具有通透性的大鼠心室肌细胞悬液中，已对钙离子交换进行了测量。鉴定出了两种交换组分，一种归因于细胞的线粒体成分，另一种归因于非线粒体组分。线粒体对钙离子的摄取被叠氮化钠阻断，且依赖于呼吸底物，而非线粒体摄取独立于这些分子发生，但依赖于三磷酸腺苷（ATP）和磷酸肌酸。非线粒体钙离子摄取可在钙离子浓度低于1微摩尔时诱导发生，其初始速率随浓度升高至100微摩尔而增加。摄取可被舒马唑（一种类似咖啡因的物质）逆转，而这种逆转又会被ryanodine抑制。这些特性表明非线粒体钙离子交换的主要位点位于肌浆网。钙离子交换可被多种试剂调节，包括肌肽，但不受其他物质影响，包括钠离子、肌醇三磷酸和环磷酸腺苷。给出了数据的动力学模型，该模型纳入了线粒体组分中钙离子摄取的类似数据。在这些实验中测量的钙离子交换速率表明，细胞的这两个组分能够足够迅速地降低肌浆钙离子浓度，以解释所观察到的等长收缩的瞬态性质。此外，有人提出细胞的非线粒体和线粒体组分都可能对大鼠心肌的张力松弛有显著贡献。
