Heart Keeps Pumping Out New Cells

　　The heart-stopping news from Stockholm is that the heart never stops—growing, that is. Because researchers have shown that the human heart continues to produce muscle cells, even in adults.

　　Scientists have long debated whether the heart was capable of regeneration. They could make heart cells divide in a culture dish. But no one knew whether the cells could do the same in a living organism.

　　To find out, the Swedish scientists literally took advantage of fallout from the Cold War. The testing of nuclear weapons in the 1950s spewed a lot of radioactive carbon-14 into the air. That C-14 then got incorporated into the cells of every plant and animal on earth. When testing was banned in the ‘60s, C-14 levels dropped.

　　Those changing levels of radioactive carbon could be used to estimate when individual cells in the body, and in the heart, arose. Using this C-14 dating, the scientists found that a 25-year-old replaces about 1 percent of his heart cells a year, and a 75-year-old about half that, data published in the journal Science. The turnover is a tad slow but it does offer hope that damaged hearts might someday be made to mend themselves.

　　心脏一直都在生成新细胞

　　心脏从没有停止生长，这是来自斯德哥尔摩的振奋人心的消息。研究者们显示即使对于成年人来说，心脏一直在生成肌细胞。

　　科学家们一直争论心脏是否有再生的能力。他们可以在培养皿中让心脏细胞分裂。但是没有任何人知道是否这些心脏细胞在活的生物体内一样能够分裂。

　　为了探明究竟，事实上这些科学家们研究了冷战期间核军备竞赛所留下的放射性尘埃。上个世纪50年代的核武器试验的结果导致向空气中排放了大量的放射性碳14。这些碳14进入到地球上各种动植物的细胞中。在60年代，核试验被禁之后，碳14的水平也下降了。

　　放射性碳的这种变化水平可以用于估测身体中以及心脏中个体细胞是何时开始生成的。这些科学家们使用碳14测年法发现，一名25岁的人一年更新大约1%的心脏细胞，而一名75岁的人一年更新大约0.5%的心脏细胞，这些数据发表在《科学》（Science）杂志上。虽然心脏细胞的这种“更新率”有点儿慢，但是这确实给人们带来了希望：将来受损的心脏可能可以自愈。