by Angela Spivey

latelets—cells that form the first sticky plug of a blood clot—are activated by an enzyme called thrombin. When one platelet gets activated, it sends a signal to another platelet to activate, and so on. If platelets activate when they’re not supposed to, you can develop a dangerous clotting of the veins. To learn how the body keeps clotting under control, JoAnn Trejo, assistant professor of pharmacology, studies the receptor for thrombin on a platelet’s surface.

Once thrombin’s receptors have done their job, they are removed from the cell surface to a compartment within the cell called the lysosome, which degrades the receptor ("chops" it into its single amino acids). This degrading is an unusual aspect of thrombin’s receptors. Many other types of receptors are recycled—they move to the inside of the cell, are modified slightly, and then return to the cell surface in an "off" state, ready to signal again.

"To get new receptors for thrombin back on the cell surface, the cell has to synthesize more receptors, and that costs a lot of energy," Trejo says. "So it’s not a very efficient system." But it’s an important one. Receptors for thrombin have to be degraded, Trejo says, because if they return to the surface, they can continue to signal.

But Trejo has found that thrombin’s receptors take the same pathway to get inside the cell as receptors that are recycled. So she thinks that there must be something particular about thrombin’s receptor that says to the cell "degrade me." Her next step is figuring out how the receptor does that.

Discuss this story.

© 2001 Endeavors, The University of North Carolina at Chapel Hill. All rights reserved.