Adjustment in Cellular Calcium Delivery Impacts Eye, Brain Function

BALTIMOREResearchers at the Johns Hopkins University School of Medicine published research uncovered details on the molecular mechanism behind a mutation in a calcium channel protein that shuttles calcium in and out of cells, which has potential to address not only congenital stationary night blindness but also other neurodegenerative conditions including Parkinsons and Alzheimers diseases.

Calcium is so crucial for normal functions like heart contraction, insulin control and brain function, said David Yue, M.D., Ph.D., a professor of biomedical engineering and director of the Calcium Signals Lab at Hopkins. If calcium levels are off at any time, disease can ensue. Our new approach, watching calcium channels in action in living cells, allowed us to tease apart how they behave and how theyre controlled and find a new module that could be targeted for drug design.

The aberrant calcium channel protein that causes this type of night blindness is missing the tail end of the protein. Yues team compared the ability of this protein to full length versions by examining how well they can maintain electrical current in cells. Normal channels show a decrease in current with an increase in calcium levels. We and others initially believed that the missing piece of the protein might behave to simply switch off the ability of elevated intracellular calcium to inhibit this current, Yue said. Without this module, theres no way to down-regulate the calcium entering through these channels.

However, the module actually appears to function in a more nuanced manner. Calcium channels are known to be controlled by the protein CaM, which senses and binds to calcium, whereupon CaM binds to channels in a manner that inhibits their calcium transport function. To figure out how the tail module works in conjunction with CaM to control the calcium channel, the team used a molecular optical sensor tool that enabled them to see in live cells different levels of CaM, a controller of the channel protein. When CaM is abundant, the sensor glows cyan; when CaM is low, the sensor glows yellow.

The researchers found the tail module doesnt simply turn off channel sensitivity to calcium; rather, the module smoothly retunes how sensitive channels are to CaM, and in turn how sensitive the transport function of channels is to intracellular calcium. In all, the tail module smoothly adjusts how much calcium enters cells. This manner of adjustment may bear on many neurodegenerative diseases where calcium is dysregulated, Yue said. With the optical sensor, Yue and his team next will examine other types of live cells, including nerve and heart cells, to measure whether changes in calcium channel behavior can lead to disease-like states.

The study was funded by the National Institute of Mental Health, the National Heart, Lung and Blood Institute and the National Institute on Deafness and Other Communication Disorders, and was published by the journal Nature (ePub 18 Feb 2010. 463:968-972; DOI:10.1038/nature08766).