Although secretions like saliva and digestive juices might have a high ick-factor, these bodily products are essential for us to function normally. When these secretory processes go awry in humans, conditions like dry mouth might arise. And a more severe form of that—Sjögren’s syndrome—causes more inconvenience and detriment in otherwise mundane activities such as eating and speaking.

A new study in Science Signaling has uncovered how our bodies secrete the natural juices that keep us going. And at the heart of this process is calcium—a molecule that acts as a gatekeeper in our bodies. Calcium is broadly involved in secretions, and not just those limited to digestion. For instance, secretions that occur between nerve cells allow neighboring cells to communicate with each other, sending signals from our brains to farther regions of our bodies.

In our cells, calcium is stored in a network of tubule-looking structures where proteins are synthesized, called the endoplasmic reticulum (ER). Signals can trigger the release of calcium from the ER into the cell itself, which can then cause saliva and other secretions to be released out of the cell. To get from inside the ER to the outside, calcium passes through what’s called an IP3 receptor. These IP3 receptors are complex, and are made of four units, all of which work in conjunction to let calcium flow out of their reserves.

Until this new study, researchers weren’t exactly sure how the four units of the IP3 receptors cooperated to let calcium out of the ER. This new study, conducted by a group of researchers at the University of Rochester of Medicine and Dentistry in New York, found that the IP3 receptor only opens under very stringent conditions. The IP3 molecule needs to not bind to just one unit of the receptor, but all four, in order for calcium to be released. If this calcium channel were not controlled as stringently, then cells could start over-secreting. And, too much of a good thing, they say—in this case, of calcium—could be toxic to human cells.

While this new study has broad implications for secretory disorders in humans—extending to those that affect our nervous and immune systems—it also, at the very least, highlights the importance of secretions in our lives.



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Science Progress, Vol. 64, No. 253 (Spring 1977), pp. 95-115
Science Reviews 2000 Ltd.