细胞如何控制离子的进出

A common protein plays a different role than previously¹ thought in the opening and closing of channels that let ions flow in and out of our cells, researchers at Johns Hopkins report. Those channels are critical to life, as having the right concentrations of sodium² and calcium³ ions in cells enables healthy brain communication, heart contraction⁴ and many other processes. The new study reveals that a form of calmodulin long thought to be dormant⁵ actually opens these channels wide. The finding is likely to bring new insight into disorders⁶ caused by faulty control of these channels, such as cardiac arrhythmias, epilepsy and Parkinson's disease, the researchers say. A report on the finding appears in the Oct. 23 issue of the journal Cell.   In the current model, explains David Yue, M.D., Ph.D. , a professor of biomedical engineering and neuroscience at the Johns Hopkins University School of Medicine, calmodulin can do little until it binds⁸ to calcium, which changes its shape and snaps it into action. The activated⁹ calmodulin can then bind⁷ to a specialized¹⁰ control lever inside calcium and sodium channels, which closes the channels.   The new study revises this viewpoint by devising ways to deliver surges of calcium-free calmodulin to channels. In so doing, "it can be seen that calcium-free calmodulin is in no way dormant, but instead markedly boosts the opening of calcium and sodium channels to begin with," Yue says. When calcium binds to the "resident" calcium-free calmodulin on channels, this initial enhancement dissipates. "The two forms of calmodulin are both powerful, each imposing¹¹ opposing actions that together maintain exquisite¹² control, akin¹³ to the 'yin-yang' balance in Chinese philosophy," Yue says. "This insight into how the calmodulin-controlled lever works could ultimately help in finding treatments for a plethora¹⁴ of conditions that stem from faulty ion channels."