ATP-DEPENDENT CA-2+-PUMPING SYSTEM IN DOG HEART SARCOLEMMA
ATP-DEPENDENT CA-2+-PUMPING SYSTEM IN DOG HEART SARCOLEMMA
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DOI：
10.1038/283765a0
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发表时间：
1980-01-01
期刊：
影响因子：
64.8
通讯作者：
CARAFOLI, E
中科院分区：
文献类型：
--
作者：
CARONI, P;CARAFOLI, E
Since the pioneering studies of Ringer of almost a century ago1,2, it has been known that the contraction of heart cells requires the presence of calcium in the extracellular medium. Ca2+penetrates into the sarcoplasm where it either directly activates troponin C (ref. 3), or indirectly conveys the contraction signal to the myofibrils, possibly by inducing Ca2+release from intracellular stores (sarcoplasmic reticulum, SR)4–6. After contraction Ca2+must obviously leave the heart cell again to prevent its progressive accumulation. As the electrochemical potential of Ca2+across the sarcolemma would prevent its passive outflow, the efflux of Ca2+is an energy requiring process. Most of the Ca2+is apparently ejected from heart cells in exchange for Na+(refs 7, 8), on an electrophoretic antiporter which exchanges three Na+ions for one Ca2+(ref. 9). However, there is some evidence10–14of a specific ATPase in cardiac sarcolemma, which could also have a role in the energy-dependent ejection of Ca2+. One important difficulty in trying to establish the existence of a specific Ca2+-ATPase in cardiac sarcolemma lies in the fact that most of the preparations used in such studies have been heavily contaminated by other sub-cellular fractions (mitochondria, SR) which also possess ATP-dependent Ca2+transporting systems. In the present work we describe an ATP-dependent Ca2+transport system which can be conclusively ascribed to heart sarcolemma. We show that a heart vesicular preparation particularly enriched in sarcolemma markers accumulates Ca2+in the presence of ATP. That the process takes place in sarcolemmal vesicles is demonstrated by the fact that the accumulated Ca2+is promptly and completely released in exchange for Na+.
